The Content and Structure of Schizotypy: A Study Using Confirmatory Factor Analysis

Transcription

1 The Content and Structure of Schizotypy: A Study Using Confirmatory Factor Analysis Abstract This study examined the content of subscales within a multidimensional scale of self-reported schizotypy and their subsequent interrelationship by means of confirmatory factor analysis (CFA). Neither single-factor nor four-factor models provided good fits to the data; two-factor and three-factor models showed very good fits. On closer look, the three-factor solution was, overall, marginally the best fit and gave credence to a model with positive schizotypy, negative schizotypy, and social impairment as the factors. This model was in contrast to those that have disorganization as the third factor. In the present study, the subscale of disorganization loaded on the factor of positive schizotypy. The three-factor solution proposed here may be seen as giving support to the structures advocated by Meehl (1962), Strauss et al. (1974), and Lenzenweger et al. (1991). Keywords: Schizotypy, positive, negative, social impairment, disorganization, confirmatory factor analysis. Schizophrenia Bulletin, 26(3): , This study has the sole aim of examining the structure and content of schizotypy; while using a scale for its measurement, it does not set out with the immediate intention of producing an instrument for practical use. A study of this kind inevitably necessitates an examination of the present position of the subject in light of the ways in which this position has been reached. This is particularly the case if parallels are to be drawn between schizotypy and schizophrenia. The current position of work on schizotypy, or schizotypal personality, may be thought of as having two major historical origins. The first, starting with the work of Kety et al. (1968) on the Danish adoption studies, showed that the relatives of schizophrenia patients tended to exhibit symptoms labeled as "borderline state." After by Peter H. Venables and Neil A. ector the work of Spitzer et al. (1979), this diagnosis would become schizotypal personality disorder (SPD) in DSM-H1 (American Psychiatric Association [APA] 1980) and now DSM-IV (APA 1994). Kendler et al. (1981), using SPD as the diagnostic tool, subsequently replicated the earlier finding of Kety et al. and thus identified a personality disorder that had familial associations with schizophrenia. To extend work on this topic, aine subsequently developed the Schizotypal Personality Questionnaire (SPQ), with subscales to represent the nine aspects of SPD (aine 1991). The second historical origin can be traced from the work of ado (1960) and through the influential statements of Meehl (1962), who designated four cardinal aspects of schizotypy as "cognitive slippage," "interpersonal aversiveness," "anhedonia," and "ambivalence." A somewhat similar concept had been put forward by Hoch and Cattell (1959), who suggested that "pseudoneurotic schizophrenia" was a possible diagnosis for a group of patients having symptoms with some affinity to those of schizophrenia. The Meehl approach was further developed by the Chapmans (see Chapman et al. 1995, pp , for a recent description of their work), resulting in the use of five scales: physical anhedonia, social anhedonia, perceptual aberration, magical ideation, and impulsive nonconformity. The scales of perceptual aberration and magical ideation were found to be so highly correlated that they were later combined into a single group (Per-Mag). A third historical path is that traced by Nielsen and Petersen (1976), who derived their approach from the work of Chapman (1966) on the symptoms of early schizophrenia. This work resulted in a set of items that provided a scale of "schizophrenism" that was related to electrodermal activity. This relationship was in the same Send reprint requests to Prof. P.H. Venables, Dept. of Psychology, University of York, Heslington, York, YO10 5DD, United Kingdom; e- mail: phv@venables.u-net.com. 587

2 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector direction to that which had been shown by Mednick and Schulsinger (1968) to identify children at high risk for schizophrenia. Venables and Bailes (1994), Venables (1995), and Vollema and Vandenbosch (1995) recently provided reviews on the structure of schizotypy and the relation of this structure to that of schizophrenia. The apparent similarity of structures found in schizotypy and schizophrenia does not necessarily establish an underlying similarity of etiology of the two diagnoses. However, arguments rehearsed in the three papers give general support for the Meehl (1962, 1990) model of a common neurointegrative defect, "schizotaxia," that underlies schizotypy in those exposed to benign environments and gives rise to schizophrenia in those exposed to negative experiences. It is thus useful to bear in mind that the issues raised about the content of dimensions when identifying the structure of schizophrenia may be the same as those considered when examining the content of schizotypic dimensions. To take such a stance does not necessarily mean uncritical acceptance of a full parallelism between schizotypy and schizophrenia. Venables and Bailes (1994), Venables (1995), and Vollema and Vandenbosch (1995) have suggested that schizotypy is multidimensional and that established dimensions may be thought of as (1) positive, characterized by unusual perceptual experiences and magical ideation, and (2) negative, having loadings on physical anhedonia and social anhedonia (including interpersonal aversiveness and social anxiety) with a high negative loading on extroversion. There is less unanimity about the content or even the inclusion of a third factor that was labeled "disorganization/social anxiety" by Bentall et al. (1989). While a fourth factor, impulsive nonconformity with high loading on Eysenck (1992) "psychoticism," (P), is clearly present when measured by suitable scales and is shown to be orthogonal to the positive and negative dimensions, it is arguably not an established aspect of schizotypy (or schizophrenia). It does not, for instance, appear as an element of SPD, nor does its inclusion directly follow from the ado-meehl origin. While a good case is made for its inclusion by Chapman et al. (1984), the present study had as its aim the further elucidation of the clearly positive and negative aspects of schizotypy and the possible inclusion of a third factor; therefore, we did not examine the role of the putative nonconformity fourth factor. In contrast, the dimensions of schizophrenia may be thought of as better established. They are, in summary, (1) positive, characterized by hallucinations and delusions; (2) negative, characterized by avolition, anhedonia, alogia, and flattening of affect; and (3) disorganization, with thought disorder being a consistent identifier, together with poverty of speech content and bizarre behavior. Another version of the three-syndrome model is that of Strauss et al. (1974), where the third syndrome is that of "disorder of relating" rather than disorganization. This structure is supported by the later analysis of Lenzenweger et al. (1991). The ambiguity of the labeling of the third dimension in work on schizophrenia is reflected in the labeling of its counterpart in schizotypy as "disorganization/social anxiety." There has thus been a movement away from the two-dimensional structure outlined by Crow (1980), with its view of a distinct etiologic difference between the two dimensions and the structure originally proposed by Andreasen and Olsen (1982), where negative schizophrenia and positive schizophrenia were expressed as opposite ends of a bipolar dimension. The position that has been reviewed thus suggests a degree of apparent parallelism between the models of schizotypy and schizophrenia. However, questions arise about the content of scales used and the content of concepts with apparently similar-sounding labels. One major difficulty that arises in the self-report measurement of schizotypy is that of framing the content of questionnaire items to be answered by normal subjects in any way to reflect the content of symptoms observed in overtly ill patients in a clinical situation. One of the most obvious differences between the content of the negative dimension in schizotypy and the content of the negative dimension in schizophrenia is that in schizotypy the content has been measured in many cases by anhedonia scales, whereas a wider range of symptoms is found in schizophrenia. A further anomaly is that studies on schizotypy arising from the Meehl-Chapman tradition (e.g., Chapman et al. 1976) rely on physical and social anhedonia as identifiers of negative schizotypy, whereas the DSM definition of SPD (APA 1994) does not include anhedonia as one of its identifying characteristics. There are thus, at this stage, two main problems in the conceptualization of the structure and content of schizotypy. The first concerns the content of the negative dimension; should it, in addition to anhedonia, contain features such as avolition, alogia, and flattening of affect features that are the content of the negative dimension of schizophrenia? The second concerns the content of the third "disorganization/social anxiety" dimension; should it be restricted to disorganization and is social anxiety another dimension, or do the two occur together? In addition to these considerations, there are more minor ones raised in studies of the structure of schizophrenia that are concerned with the detail of the content of such concepts as alogia. Many of the studies analyzing data from schizophrenia patients use the Scale for the Assessment of Negative Symptoms (Andreasen 1984a), 588

3 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, 2000 and the question arises whether alogia is a component of the negative symptom factor or of the disorganization factors. The issue appeared to be resolved by Liddle (Liddle 1987; Liddle and Barnes 1990), who, by separate use of the subscales that define alogia, showed that "poverty of speech" was a negative symptom item while "poverty of speech content" loaded on the disorganization factor. Andreasen et al. (1995) provide data to support this finding. However, the issue is unresolved in that Peralta et al. (1992), in a similar study, showed that poverty of speech content has its main loading on the negative symptom factor. A further issue that arises principally from the consideration of the literature on schizotypy is the position of magical ideation. Chapman and Chapman (1987), for instance, have shown that it is appropriate to use their Perceptual Aberration Scale (Chapman et al., 1978) and the Magical Ideation Scale (Eckblad and Chapman 1983) together as a combined scale (Per-Mag), because the two scales have been generally shown to be highly correlated. Some doubt may be raised about this procedure by the finding of Kendler and Hewitt (1992) that magical ideation has a strong genetic component but perceptual aberration does not. Work in preparation by Bailes and Venables analyzes a magical ideation scale in the context of the Venables et al. (1990) schizotypy scale. This scale contains some of the Eckblad and Chapman (1983) magical ideation items, which load on a positive schizotypy factor. Other items in the new scale form three factors that might be labeled "astrology/fortune telling," "belief in extra-terrestrial beings," and the "effect of supernatural forces." The DSM-TV diagnostic criteria for both schizophrenia (prodromal or residual symptoms) and SPD contain the items "odd belief or magical thinking" (e.g., superstitiousness and beliefs in clairvoyance, telepathy, and a sixth sense) and that "others can feel my feelings"; however, the item "unusual perceptual experiences" also contains the item "sensing the presence of a force or person not actually present," which also might be thought of as magical thinking. The definition of magical ideation thus appears to require more analysis. aine et al. (1994) carried out CFAs of the SPQ (aine, 1991), which as stated above, was designed to tap the nine features of SPD. They found that a three-factor model provided the best fit to the data. The factor "cognitive/perceptual" loaded on scales labeled "ideas of reference," "magical thinking," "unusual perceptual experiences," and "suspiciousness/paranoid ideation"; the factor "interpersonal" loaded on the scales "suspiciousness/paranoid ideation," "social anxiety," "no close friends," and "constricted affect." Finally, the factor "disorganization" loaded on the scales "odd behavior" and "odd speech." aine et al. (1994) drew attention to the possible analogy between their factor structure and the three-dimensional, positive-negative-disorganization structure of schizophrenic symptoms. Thus, in the analysis of the SPQ (which contains no anhedonic items), the analogue to negative symptom schizophrenia is replaced by the factor designated "interpersonal." It is to be noted that paranoid ideation loaded on both the first and second factors. A similar solution was found by Gruzelier et al. (1995), using an exploratory factor analysis of the SPQ with varimax rotation. Factor 1, entitled "withdrawn" by Gruzelier et al. (1995), had the same pattern of loadings as aine et al.'s interpersonal factor. Factor 2, labeled "unreality," loaded on the same scales as aine et al.'s cognitive/perceptual factor. Factor 3, labeled "active" by Gruzelier et al., was identical to the disorganization factor of aine et al. Again, paranoid ideation was crossloaded on the cognitive/perceptual and interpersonal factors. Gruzelier et al. drew particular attention to the parallels between this three-syndrome structure and those shown recently in work on schizophrenia. Mason (1995), using CFA on data collected by the CSTQ which had been constructed by Bentall et al. (1989), essentially replicated the findings of these latter authors and showed a four-factor structure for schizotypy. Bentall et al. (1989) included measures that defined a factor of impulsive nonconformity, and this was also found by Mason (1995). The remaining three factors fit closely with those found by aine et al. (1994) and Gruzelier et al. (1995). They are labeled by Mason (1995) as "unusual perceptual experiences," "cognitive disorganization," and "introvertive-anhedonia," where the last factor is defined by social and physical anhedonia and introversion, in contrast to the interpersonal factor of aine et al. (1994), which has some of the same connotations as "introvertive anhedonia" but is defined by "no close friends" and "social anxiety." In most of the studies reviewed above, labeled aspects of schizotypy are measured by scales whose items are dependent on clinical judgment. Assessment of whether items reflect clinical definitions and measures of scale reliability determine their item content. Factor analysis using items as the input was employed by Venables et al. (1990) and Venables and Bailes (1994). In the former study, a two-factor structure was found; in the latter, four factors were apparent with the labels of "unusual perceptual experiences/paranoid and magical ideation," "social anxiety/disorganization," "physical anhedonia," and "social anhedonia." In the Venables and Bailes (1994) study, the items entering the first two factors are those that define a single factor of positive schizotypy in the Venables et al. (1990) study. Also in this latter study, both aspects of anhedonia are combined in a single factor. The independence of factors 1 and 2 in the 589

4 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Venables and Bailes (1994) study is questioned by the finding that the scales defining these factors have an intercorrelation of With these considerations in mind, the present study was designed as an attempt to answer questions centered around two issues: first, the unidimensionality of scales whose content might be thought to reflect some of the concepts outlined above; and second, the ways these scales might interrelate to form a structure of schizotypy that reflects some of the ideas established in earlier work. As the main aim was to establish the number of factors needed to describe a data set, this study used CFA rather than exploratory factor analysis, which has the failing of not being able to identify unequivocally the number of factors in a solution. Measures of goodness of fit of hypothesized structures made such an aim feasible. It should be reemphasized at this point that the set of items used to examine some of the issues outlined above is not intended, at this stage, to immediately provide a usable instrument, nor did we intend to examine the validity of the scale or subscales produced. ather, this must be considered as an experimental study that sets out with the sole aim of examining the dimensional structure and content of schizotypy. It is also important at this stage to state that both exploratory and CFA procedures are capable of addressing only the dimensional aspects of a set of variables and are not capable of examining the issue of whether schizophrenia or schizotypy are qualitative or quantitative in nature. A dimensional approach, as adopted here, necessarily makes an assumption of the validity of a quantitative model. An attempt to make a decision between eventual quantitivity or qualitivity may be undertaken by other techniques such as taxometric analysis; however, the issue is wider than this in that it can depend on whether changes in fundamental brain systems produce continuous changes in behavior or can in certain instances produce step-wise changes or changes that appear to socially significant others to be of a step-wise nature. Stage 1 of our study examined the content of single subscales. The hypotheses used as points of departure were as follows: 1. There is a unidimensional "positive schizotypy" subscale that contains both unusual perceptual experiences/perceptual aberration items and magical ideation items. 2. There is a unidimensional "disorganization" subscale that includes alogia. 3. There is a unidimensional "negative schizotypy" subscale that includes aspects of anhedonia, social impairment, poverty of speech, and flatness of affect. Stage 2 of our study examined the way in which the single subscales from stage 1 together form the structure of schizotypy. The hypotheses used as points of departure were as follows: 4. The subscales, taken together, form a single dimension. 5. On the basis of some of the foregoing studies, particularly those that show a high correlation between positive schizotypy and disorganization, a two-factor model may be posited. 6. On the basis of the data reviewed earlier, a three-factor structure may be suggested with the factors being positive schizotypy, negative schizotypy, and either disorganization or social impairment. 7. Based on the work of Lenzenweger and Dworkin (1996), a four-factor structure may be suggested with the third factor of disorganization being split into disorganization and social impairment. These hypotheses form only the starting points of the study; the analysis of the ways in which individual items are taken to form the content of subscales in stage 1 and the ways in which the scales are linked in successive models in stage 2 will be outlined in the esults section. Method The Questionnaire. The questionnaire was developed from the 30-item version described by Venables et al. (1990) by the inclusion of 20 further items. In particular, items were included that might enable the concept of negative schizotypy to extend beyond that of anhedonia. The questionnaire is shown in table 1, where the hypothesized content of each item is given. Items are grouped in the subscales that arise from the analyses carried out in stage 1. The same principle that informed the construction of the 30-item scale was used in this instance, namely, that the item content should be such that as little evidence as possible is given to normal subjects that the questionnaire was intended to tap behavior that at its extreme might be considered abnormal. The extent to which this precept was followed, particularly in the case of items tapping magical ideation, might be questioned. However, some sense that the subjects did not view such items as number 25, "Those who practice witchcraft can affect other people's lives" as "abnormal" was shown by the fact that, surprisingly, 47 percent of the sample population answered "true" to this item. All items were answered true or false, but the direction of scoring of those items marked in table 1 was reversed so that all items were scored in the same direction. Subjects. Three hundred and thirty normal subjects were drawn from tertiary education colleges. Their mean age was ± 5.89 years. Eighty-six subjects were men and 590

5 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, 2000 Table 1. Experimental questionnaire 1 Item Hypothesized item content Positive symptoms 8. I often change between positive and negative feelings towards the same person often get a restless feeling that I want something but do not know what. 27. Now and then when I look in the mirror, my face seems quite different from usual. 31. I feel that I have to be on my guard, even with friends. 36. I am occasionally bothered by the feeling that other people are watching me. 41. At times I am distracted by sounds that I am not normally aware of. 43. Sometimes people who I know well begin to look like strangers. 47. I have sometimes felt that strangers were reading my mind. 49. I think that it is important to keep an eye out to stop people taking advantage of me. Magical ideation 13. It is not possible to harm people merely by thinking bad thoughts about them. 15. It is my opinion that the earth is solely controlled by the laws of nature. 25. Those who practice witchcraft can affect other people's lives. 26. When introduced to strangers I often wonder whether I have known them before. 33. I think supernatural forces can affect our lives. 39. I believe that many of the bad things that happen in the world are due to the force of evil. 45. Some people have the power to cast evil spells. Disorganization 1. I am not easily confused if a number of things happen at the same time. 6. I think of myself as being quick in my actions. 19. Sometimes I find that I am not very clear when answering peoples' questions. 23. I find it difficult to concentrate; irrelevant things seem to distract me. 28. I often feel tired or lethargic. 29. People can easily influence me even when I thought my mind was made up on the subject. 32. I often have grave difficulties controlling my thoughts when I am thinking. 40. I prefer others to make decisions for me. 50. I find that I sometimes wander off the point when talking to people. Positive schizotypy Positive schizotypy Positive schizotypy Paranoid ideation Paranoid ideation Positive schizotypy 2 Magical ideation 3 Magical ideation 3 Paranoid ideation Magical ideation 3 Magical ideation 4 Magical ideation 4 Magical ideation 3 Magical ideation 4 Magical ideation 4 Magical ideation 4 Disorganization? Disorganization Disorganization Disorganization? Disorganization Disorganization Disorganization Disorganization Disorganization Social avoidance 2. I sometimes avoid going to places where there will be a lot of people because I know I will get anxious. Social avoidance 7. I never find it difficult to talk in a group of people. Social avoidance 10. I am not much worried by humiliating experiences. Social avoidance 591

6 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Table 1. Experimental questionnaire 1 (Continued) Item 16. I suddenly feel shy when I want to talk to a stranger. Hypothesized item content Social anxiety 20. I prefer to look people in the eye when talking to them. Social avoidance Ft 22. I am not usually self-conscious. Social anhedonia 5. I attach little importance to having close friends. 9. Writing letters to friends is more trouble than it is worth. 14. When I have been extremely upset I have sometimes felt like hugging someone. 21. Getting together with old friends has been one of my greatest pleasures. 24. I tend to show my feelings and not keep them to myself. 34. When anticipating a visit from a friend I have often felt happy and excited. 44. I have thoroughly enjoyed laughing at jokes with other people. Uncommunicativeness 4. I am not good at "small talk." 12. I am mostly quiet when I am with other people. 18. I am quite expressive in my speech. 35. People say I often look serious and rarely smile. 38. The idea of going out and mixing with people at parties has always pleased me. 42. I have found that it is best not to let people know too much about me. Physical anhedonia 3. When I pass flowers I often stop to smell them. 17. Beautiful scenery is a great delight to me. 30. A brisk walk has sometimes made me feel good all over. 37. I have been fascinated with the dancing of flames in a fireplace. 46. I get a lot of pleasure from listening to music. 48. I don't understand why people enjoy looking at the stars at night. Social anxiety Social anhedonia Social anhedonia Social anhedonia Social anhedonia Flatness of affect Social anhedonia Social anhedonia 2 Poverty of speech Poverty of speech/social avoidance Flatness of affect Flatness of affect Social avoidance Paranoid ideation Physical anhedonia Physical anhedonia Physical anhedonia Physical anhedonia Physical anhedonia 2 Physical anhedonia Note. = eversed (direction of scoring is reversed). 1 The subsection headings are those that are used after scale content has been determined by modeling in the first stage of the analysis. The scale labeled magical ideation is omitted from the final model at the end of the second stage. 2 This item was omitted from scales used in the second stage of the analysis. 3 Magical ideation item from Eckblad and Chapman (1983). 4 Items from superstitiousness scale (Bailes and Venables, in preparation). 592

7 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, were women; a further 78 subjects declined to state their sex. While it is possible that the sample contained some subjects with diagnosable psychopathology, insofar as they appeared to be functioning satisfactorily it is likely that only schizotypic characteristics were being examined. Analysis. CFA was carried out using the EQS program (Bentler 1995). Goodness of fit, for assessing model adequacy, was determined by chi-square, a measure to test the discrepancy between the observed covariance matrix and the theoretically informed hypothetical model(s). A nonsignificant chi-square was an indication of a good fit. However, with large sample sizes, chi-square can be significant regardless of goodness of fit and, in consequence, other indices were also used. The Akaike Information Criterion (AIC; Akaike 1987) and the Bozdogan (1987) version, the Consistent AIC (CAIC), are presented as developments from chi-square. Smaller values of these indices represent better fitting models. Other indices used include the Normed Fit Index (NFI; Bentler and Bonett 1980) and the Non-Normed Fit Index (NNFI), developed by Bentler and Bonett (1980) from that constructed by Tucker and Lewis (1973). The NFI was revised by Bentler (1990a) to take account of sample size, as it had been shown to underestimate fit for small samples. This new index, the Comparative Fit Index (CFI), was proposed by Bentler (1990b) to be the index of choice. In the case of the stage 1 analyses, "robust" statistics were used and a corrected CFI is quoted based on the Satorra- Bentler scaled statistic (Satorra and Bentler 1988) A value of these indices greater than 0.9 is suggested to be indicative of a good fit (Bentler 1995), and a change of 0.01 is taken to indicate a significant improvement (or worsening) of fit (Wideman 1985). To enable these fit indices to be compared to those used by workers employing LISEL (Joreskog and Sorbom 1989) the Goodness of Fit Index (GFI) and the Adjusted Goodness of Fit Index (AGFI) from this program are also presented. Values of GFI greater than 0.9 are taken to indicate a good fit, while values greater than 0.8 indicate a good fit in the case of AGFI. Finally the standardized root mean squared residual (SM) is shown. In an unpublished study, Hu and Bentler reported that this index "discriminates between fitting and mis-specified models substantially better than any other fit index" (see Bentler 1995, p. 272). In addition to these goodness of fit tests, tests indicating parameters that might be added to or deleted from the model to increase fit were also used. The Lagrange Multiplier (LM) test (Lee and Bentler 1980) examines the effect of adding free parameters to a restricted model, while the Wald test (Wald 1943) examines the effect of dropping parameters. In using the LM test, Byrne (1994) makes the point (p. 48) that the suggestions it makes are based on purely statistical criteria and there must be good theoretical reason for adopting the changes suggested. For instance, as some items were thought to be not necessarily influenced by a single latent variable (suspiciousness items, for instance, were suggested above to load on both positive and interpersonal factors), the LM test provides evidence on the increase in fit that would result in the loading of an item on more than one factor. Insofar as some items may not be "good" items (in that they are not representative of any hypothesized factor in a model under consideration), the evidence of the Wald test on improvement in fit is taken into account in the model-fitting procedures described. In stage 1 the analyses are carried out with the data treated by the EQS program as categorical; the data analyzed in stage 2 are considered continuous. esults Stage 1: Analyses of the Content of Single Factors/ Latent Variables Positive schizotypy: Should this include unusual perceptual experiences, paranoid ideation, and magical ideation? Model 1 posits the existence of a single factor that might be labeled "positive schizotypy" and that is identified by the equivalents in normal subjects of hallucinations and delusions, here called "unusual perceptual experiences" and "paranoid ideation." Items supposedly measuring magical ideation were not included at this point, as it was specifically proposed to test the concern voiced in the introduction as to whether magical ideation items should be included in the "positive schizotypy" scale. The items labeled "unusual perceptual experiences" were largely derived from factor 1 in the analysis of the original 30-item questionnaire (Venables and Bailes 1994). They are identified in table 1 as "positive symptoms" items. Also included were new items labeled "paranoid ideation." The items thus included in model 1 are numbers 8, 11, 27, 31, 36, 41, and 49. The goodness of fit indices for this model, shown in table 2, indicate that the fit to a single factor is, in general, good. Model 2 examines the effect of inclusion of the three magical ideation items (26, 43, and 47) that were loaded on the first factor in the Venables and Bailes (1994) analysis and were derived from Eckblad and Chapman (1983) but were excluded from model 1. The indices for this model given in table 2 show a significant decrease in fit from model 1. Examination of the loadings on the single factor showed that for two items (26 and 41) the loadings were unacceptably low (0.27 and 0.19, respectively). The 593

8 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Table 2. Goodness of fit of models tested in stage 1 Model X 2 df P AIC CAIC NFI NNFI CFI GFI AGFI SM Note. AGFI = LISEL adjusted goodness of fit index; AIC = Akaike Information Criterion; CAIC = Consistent Akaike Information Criterion; CFI = Comparative Fit Index; GFI = LISEL goodness of fit index; NFI = Normed Fit Index; NNFI = Non-Normed Fit Index; SM = standardized root mean squared residual. Wald test indicated an improved model fit if these items were dropped. Model 3 shows that the effect of dropping these items is to significantly increase the fit, which is an improvement on model 1. The result of this analysis is to suggest that items 8, 11, 27, 31, 36, 43, 47, and 49 are the best identifiers of a factor that, for the sake of brevity, may be now labeled "positive symptoms." It was suggested in the introduction that magical ideation might be a multifactorial concept. It has already been shown above that some items which come from the Eckblad and Chapman (1983) magical ideation scale appear to fit the positive symptoms factor. Preliminary analyses indicated that the remaining item (13) from that scale is not correlated with the Eckblad and Chapman (1983) items nor with the other items labeled "magical ideation" in table 1 (15, 25, 33, 39, and 45), which are derived from the magical ideation scale from work in preparation by Bailes and Venables. Model 4 tests the extent to which these additional magical ideation items are part of the group identifying a single positive schizotypy factor. The goodness of fit indices for this model shown in table 2 indicate that such a single-factor model is not appropriate. Model 5 allows for the existence of two uncorrelated factors, "positive symptoms" loaded on the items in model 3, and "magical ideation," loaded on the items in table (15, 25, 33,39, and 45). Goodness of fit indices indicate that a two-factor solution is a good fit but that item 15 has a low loading, and the Wald test indicates that this item should be dropped. Model 6 allows the two factors to be correlated and drops item 15. There is a resulting improvement in fit, and the correlation between the two factors is only There thus appears to be a second magical ideation factor that is unrelated to the positive symptoms factor, which as seen above contains some of the Eckblad and Chapman (1983) magical ideation items. Thus, in this analysis positive schizotypy appears to have two components. Disorganization: Can it be considered to be a unitary dimension and does it include alogia? It has been seen from the literature reviewed in the introduction that a third factor after positive and negative schizotypy might be labeled "disorganization," or alternatively, "social impairment." This section of the analyses addresses the content of disorganization. Items thought to measure disorganization were 1, 23, 29, 32, and 40. Items previously included in the disorganization factor in Venables and Bailes (1994) but that might be measuring social anxiety (items 10, 16 and 22) were not included. Items 19 and 50 were added to reinforce this factor. Model 7, hypothesizing that these items form a single factor, was tested. The fit was good. Items 6 and 28, asking about speed of action or lethargy, were included in the questionnaire to test 594

9 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, 2000 whether these characteristics were part of the disorganization factor or whether, as avolition, they might be considered to characterize negative schizotypy. Model 8 tests the effect of their inclusion. The fit remains good, suggesting that self-perceived speed of reaction is part of the disorganization factor. The position of alogia as part of the disorganization factor has, as reviewed above, been the subject of controversy. Items 4 and 12 were included in the questionnaire to test whether poverty of speech was part of the disorganization factor. Model 9 tests this hypothesis. There is no longer an acceptable fit. With these two items not included, the disorganization subscale, as indicated by Model 8, is denned by items 1,6,19,23,28,29, 32,40, and 50. Negative schizotypy: Does it include aspects of social impairment, poverty of speech, and flatness of affect? The items investigating social behavior were either derived from a variety of sources or were written to tap what were thought to be aspects of behavior to which a "clinical" label of negative schizotypy might be given. Model 10 represents an initial attempt to examine how far these variables may fall into five separate but intercorrelated factors designated as "social avoidance" (tapped by items 2, 7, 10,20, and 38); "social anhedonia" (items 5,9, 21, 34, and 44); "social anxiety" (items 16 and 22); "poverty of speech" (items 4 and 12); and "flatness of affect" (items 18, 24, and 35). It must be recognized that these item associations were viewed as arbitrary at this point. It should be noted also that items 4 and 12 defining poverty of speech were being analyzed here because they had been shown in model 9 not to be part of the disorganization factor. Model 10, a five-factor solution, provides a reasonable fit to the data, but one that could evidently be improved. The correlation between the "social avoidance" subscale and the "social anxiety" subscale was 0.99 and that between the "poverty of speech" and "flatness of affect" subscales was unity. The items associated with these two pairs of subscales were therefore combined and a three-factor model, model 11, was tested. There was some slight indication of an improvement in fit. The application of Wald and LM tests showed that item 44 should be dropped and other items should change factor association. The resulting model 12 was an excellent fit. Two items, 14 and 42, had been viewed as doubtful associates with the "social factors," as they had behaved idiosyncratically in preliminary analyses. In model 13, these two items were allowed to show association with the three factors that had arisen from model 12. The goodness of fit indices associated with model 13 show that while the fit is somewhat reduced from that shown in model 12, it is nevertheless acceptable. The outcome of these analyses is that there appear to be three subscales: (1) "social avoidance," items 2, 7, 10, 16, 20 and 22; (2) "social anhedonia," items 5, 9, 14, 21, 24, and 34; and (3) "uncommunicativeness," items 4, 12, 18, 35, 38, and 42. The correlation between the first and second subscales is 0.18; between the first and third, 0.47; and between the second and third, In spite of the high correlation between social avoidance and uncommunicativeness, a model that combined these two subscales resulted in a worsening of fit. Physical anhedonia: Should physical and social anhedonia be considered a single factor? The remaining items are proposed as representatives of physical anhedonia. Model 14 shows that items 3, 17, 30, 37, 46, and 48 formed a single factor; however, item 46 had a very low loading on the factor. Model 15 indicates that these items, omitting item 46, also form a single factor that is a good fit to the data. Because some of the studies reviewed in the introduction indicated that physical and social anhedonia should be considered as a single "anhedonia" concept, model 16 tested the fit of a single factor identifying both aspects of anhedonia. The fit indices indicated that a single factor of anhedonia is a poor fit to the data. The analyses above have thus suggested the existence of seven components, all of which have some support from the literature. They are positive symptoms (PS), magical ideation (MI), disorganization (DIS), social avoidance (SAV), social anhedonia (SA), uncommunicativeness (UC) and physical anhedonia (PA). Table 3 shows the intercorrelations between the scales developed in stage I and their alpha reliabilities. These reliabilities are not high but are considered acceptable in view of the small numbers of items in each scale. Stage 2: Construction of Models To Show the Interrelation of the Subscales. It has been shown above, in model 6, that PS and MI (defined in stage 1 and not therefore as magical ideation might otherwise be interpreted) have only a very small intercorrelation, and therefore models will be examined that test whether both scales should be encompassed in a factor that might be labeled positive schizotypy. It can be expected (aine et al. 1994; Gruzelier et al. 1995) that PS, containing as it does aspects of paranoid ideation (suspiciousness), will be correlated with one or more of the "interpersonal" factors SAV or UC, which also have some paranoid aspects. The literature also suggests that DIS may be associated with the interpersonal factors, either through poverty of speech (Liddle 1987; Liddle and Barnes 1990) or poverty of speech content (Peralta et al. 1992), which may be represented by the UC factor, or through social impairment (Strauss et al. 1974; Lenzenweger et al. 1991), represented by SAV or SA. Some studies (e.g., Venables et al. 1990) suggest that SA and PA form a single factor, and 595

10 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Table 3. Correlation matrix for the scales developed in stage 1 (n = 322) 1 POS DIS SAV SA UC PA Ml POS DIS SAV SA UC PA Ml * 0.37* " *** * * *** " 0.47* * 0.21* -0.12"* * Note. DIS = disorganization (9); Ml = magical ideation (7); PA = physical anhedonia (5); POS = positive symptoms (8); SA = social anhedonia (6); SAV = social avoidance (6); UC = uncommunicativeness (6). (Numbers in parentheses indicate numbers of items in scales.) 1 Cronbach's alpha reliability values are shown in the diagonal. * p < ; ** p ; *** p < 0.05 other studies indicate that SA and PA are best treated separately. An appropriate model should clearly allow for the possibility of interrelation. Model A: Single schizotypy factor. The least likely model is that there is only a single schizotypy factor on which all scales are loaded. Examination of the fit indices in table 4 shows that such a model is not a good fit to the data. Model B: Single schizotypy without MI. Because model A provided data to show that MI had a loading of only on the single schizotypy factor and also because of the considerations at the start of this section, a model omitting MI was examined. It is shown in table 4 that there is only a minimal improvement in fit. Model C: Simple two-factor structure. In this, a structure was proposed of a positive factor made up of PS, MI, DIS, and SAV, and a negative factor made up of SA, UC, and PA, the two factors being uncorrelated. This showed an extremely poor fit. Model D: Simple two-factor structure allowing intercorrelation between factors. This model showed some improvement over model C, but the model was still not a good fit; the correlation between the two factors was Model E: As model D but omitting MI. In view of the lack of loading of MI with the positive factor in models C and D, the fit of model E was examined. There was some improvement but the fit was still not good. Model F: Two-factor structure allowing crossloading of subscales. The position of SAV and UC is somewhat anomalous. Each contains features of suspiciousness that might be considered paranoid and therefore a positive aspect of schizotypy, and each also contains aspects of social withdrawal and is therefore a part of negative schizotypy. In model F, therefore, SAV and UC are allowed to load on both positive and negative schizotypy. The fit is a considerable improvement on the other twofactor models. Model G: Two-factor structure. This model is as model F but omitting MI, which had a loading of only 0.13 on positive schizotypy. eference to table 4 shows that the fit is very good. The model structure is shown in figure 1. Model H: Three-factor structure. As indicated in the introduction, consensus of opinion is that schizotypy may be broken down into a three-factor structure: positive schizotypy, negative schizotypy, and disorganization. In model H, the positive factor was identified by PS and MI, the negative factor by PA and SA, and the disorganization factor by DIS. SAV and UC were hypothesized to load on both positive and negative factors. The fit is good but could be improved. Model I: Three-factor structure. This is an extension to model H with PS being allowed to load on the disorganization factor, as it could be argued that some element of thought disorder in PS might be related to disorganization. The correlation between the positive and disorganization factors was still allowed. Again there is a slight improvement over the previous three-factor structures. Model J: Three-factor structure. This structure was the same as in model I but with MI omitted, as had been done in the two-factor structure models E and G and because it had a loading of only 0.04 with positive schizotypy. This model was an extremely good fit and a considerable improvement over previous three-factor structures. The difficulty thrown up by this solution is that PS has a loading of only 0.27 on the factor identified as positive schizotypy, which casts doubt on the suitability of this label, hi addition, SAV has a loading of only 0.26 on negative schizotypy and the independence of PS and DIS is put in question by the fact that the factor previously designated "disorganization" was loaded 0.90 on PS and 0.53 on DIS. It has already been shown in model G that a factor of positive schizotypy has large loadings on PS, DIS, and SAV. 596

11 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, 2000 Table 4. Goodness of fit of models tested in stage 2 Model X 2 df P AIC CAIC NFI NNFI CFI GFI AGFI SM A B C D E F G H 1 J K L M ^ Note. AGFI = LISEL adjusted goodness of fit index; AIC = Akaike Information Criterion; CAIC Consistent = Akaike Information Criterion; CFI= comparative fit index; GFI = LISEL goodness of fit index; NFI = Normed Fit Index ; NNFI= Nonnormed Fit Index; SM = standardized root mean squared residual. Figure 1. Two-factor model (G) E1 E2- E Model K: Three-factor structure. This model involves the consideration of model J but also of the threefactor structure of schizophrenia put forward by Strauss et al. (1974), in which the factors are positive and negative with the third factor as "disorders of relating" rather than disorganization. The model proposed has positive schizotypy loaded on PS and DIS; negative schizotypy loaded on SA, UC, and PA; and a new factor labeled "social impairment" that, akin to Strauss et al.'s (1974) "disorder of relating," is loaded on SAV and UC. Because the paranoid aspect of social impairment might be related to positive schizotypy, correlation of these two factors is allowed. Because the social withdrawal aspect of social impairment Social Anhedonia E4 might be related to negative schizotypy, the correlation of these two factors is also allowed. The model is an excellent fit to the data. This model structure is shown in figure 2. A subsidiary analysis allowing the possibility of an intercorrelation between positive and negative schizotypy showed that this intercorrelation is only As the fit resulting from this subsidiary analysis was slightly worsened in comparison with model K, there is no case for adopting this model in preference to model K. Model L: Four-factor structure. This model tested the hypothesis of four factors: positive schizotypy, negative schizotypy, disorganization, and social impairment. The main difference between this model and model K was 597

12 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Figure 2. Three-factor model (K) E4 E E the separation of positive schizotypy and disorganization factors. Thus, the positive schizotypy factor was allowed to load on PS, the disorganization factor on DIS, and the social impairment factor on SAV and UC, while the negative factor was allowed to load on SA, PA, and UC. Interfactor correlations hypothesized were those between positive schizotypy and disorganization, between social impairment and positive schizotypy, and between disorganization and negative schizotypy. The fit, as shown in table 4, was not as good as that for the three-factor solution model K. Model M: Four-factor structure after Peralta et al. (1994). Peralta et al. (1994), in an analysis of schizophrenic symptoms measured by SANS (Andreasen 1984a) and the Scale for the Assessment of Positive Symptoms (SAPS; Andreasen 1984b), showed that a fourfactor solution provided the best fit to their data. An attempt to replicate this solution was made with the present data. The model follows closely that shown above as model L. However, in model M the correlations between factors were those given by Peralta et al. (1994, table 3, p. 732). eference to table 4 shows that this model was not a good fit. Discussion The immediate outcome of this model-fitting exercise is that two models, G and K, provide good fits to the data. On all but one of the fit indices, however, model K (the three-factor solution) is the better fit. The three-factor solution identifies a positive schizotypy factor loaded on the subscales PS (positive symptoms) and DIS (disorganization), a social impairment factor loaded on SAV (social avoidance) and UC 0.76 E E E7 (uncommunicativeness), and a negative schizotypy factor loaded on SA (social anhedonia), UC (uncommunicativeness), and PA (physical anhedonia). The structure is fairly simple in that the only subscale that is cross-loaded is UC, which loads on both social impairment and negative schizotypy. The link between cognitive/perceptual and interpersonal components, as exemplified by the Gruzelier et al. (1995) and aine et al. (1994) studies, was through an interfactor correlation of 0.70 rather than suspiciousness or paranoid tendency being loaded on both factors. Although the three-factor solution is the preferred one, both it and the two-factor solution present the same problem. Where both models depart most markedly from the aine and also the Gruzelier structures is that PS and DIS are both loaded on the same factor, labeled here "positive schizotypy," rather than there being separate factors of cognitive/perceptual or positive symptoms and disorganization. It should be noted, however, that aine et al. (1994) reported correlations of 0.71 and 0.75 between these factors and that awlings and Macfarlane (1994), in a study similar to the present one in that it uses scales specifically constructed to measure limited aspects of schizotypy, report that "cognitive disorganization" has a loading of 0.78 on a factor of positive schizotypy in both two- and three-factor solutions. Mason (1995) in a CFA study using a wide variety of general scales (the Combined Schizotypal Traits Questionnaire; Bentall et al. 1989) reported the best fit to a model with unusual perceptual experiences and cognitive disorganization as separate factors; however, an oblique solution that provided the best fit showed a correlation of 0.62 between the two factors. Finally, Coleman, et al. (1996) showed that subjects identified by their high scores on the Chapman Perceptual Aberration Scale (Chapman et al. 1978) had higher scores on measures of thought disorder than those 598

13 The Content and Structure of Schizotypy Schizophrenia Bulletin, Vol. 26, No. 3, 2000 with low perceptual aberration scores. As thought disorder may be considered to be an aspect of the concept of cognitive disorganization, this is further evidence of the close association between disorganization and positive aspects of schizotypy. However, the apparent overlap between the components of positive schizotypy and disorganization that arises from the present study and those reviewed does not however necessarily mean that there is a unitary basis for the two concepts. It is perfectly possible to have two systems that are separate but influence each other. Gruzelier and Doig (1996), in work on schizophrenia, distinguishes the syndromes or factors that they label "active" (analogous to that labeled "disorganization" in other studies) and "withdrawn" (akin to that labeled "negative" in other studies) on the basis of the lateral asymmetry of the electrodermal responses shown by subjects predominantly showing these characteristics, whereas a third syndrome defined by Schneiderian first rank symptoms (Schneider 1959) and labeled "unreality" has no or inconsistent lateral associations. Liddle (1987) and Liddle and Barnes (1990), working with patients with chronic schizophrenia, advocate a three-syndrome model of "reality distortion," "disorganization," and "psychomotor poverty." This model has close parallels to the positive, disorganization, negative syndrome models outlined above. Liddle et al. (1992) examined cerebral blood flow patterns in patients with persistent symptom patterns characteristic of these syndromes. They were able to show different patterns of blood flow in the different groups of patients. Those patients characterized as showing reality distortion had a locus of maximal activation in the parahippocampal gyrus, while those showing disorganization had a locus of maximal activation in the anterior cingulate cortex. These differences were obtained during performances on different tasks, but the results are quoted here to suggest that positive and disorganization syndromes, although shown in the present study to be positively related, may be functionally related to different cerebral mechanisms with functional interconnections. Venables (1995) reviews further material suggesting that although the syndromes of positive symptoms and disorganization are correlated, they may have different underlying mechanisms and behavioral associations. In the model adopted here, the scale labeled "magical ideation" was omitted because this scale for MI did not have, in this set of data, any relation to any of the other scales. However, the three magical ideation items derived from the Eckblad and Chapman (1983) scale (items 26, 43, and 47) were shown in model 2 to form part of the positive symptom subscale alongside "unusual perceptual experiences." The common characteristic of these three Eckblad and Chapman (1983) items is that they are all concerned with reaction to strangers and can possibly be interpreted as relating more to delusional behavior than to magical ideation as defined by DSM-1V and to some extent tapped by the items omitted from the final model. More work should be done on this concept. One of the difficulties with the definition of negative schizotypy in earlier studies is that it has been associated mainly with anhedonia and not with the characteristics used to define negative schizophrenia, such as avolition, anhedonia, affective flattening, alogia, and attentional defect. This study has widened the definition of negative schizotypy by showing that while it is defined by both social and physical anhedonia, it also has loadings on what has been here called uncommunicativeness. It should also be noted that the factor of negative schizotypy is intercorrelated with the factor labeled as "social impairment." The favored model K is perhaps nearest to those advocated by Strauss et al. (1974) and Lenzenweger et al. (1991) in work on schizophrenia in which the third factor, after positive and negative schizophrenia, was labeled "disorder of relating," rather than "disorganization," which had been the third factor on other studies. In the work of Strauss et al. (1974), "disorders of relating" have a special position as predictors of later dysfunction and continue as disorders predicting the poor recovery of positive and negative symptoms of schizophrenia. However, in this instance, the three aspects of schizophrenic symptomatology are made on the basis of clinical judgment and without subsequent statistical analysis. Lenzenweger et al. (1991), on the other hand, use CFA to produce a three-dimensional model that parallels that of Strauss et al. The third factor again has a social impairment connotation and is derived from scales of poor premorbid function. As discussed earlier, the extent to which structures that arise from work on schizophrenia can be expected to be paralleled in work on schizotypy must also be open to discussion. However, if we take the view of Strauss et al. (1974) that social impairment is a feature that continues from the premorbid to the morbid state, it would appear to be an acceptable dimension of schizotypy. It should also be noted that the three-factor structure exemplified in model K may be seen as a reflection of three of Meehl's (1962) cardinal aspects of schizotypy: "cognitive slippage," "interpersonal aversiveness," and "anhedonia." More recently, Lenzenweger and Dworkin (1996), analyzing similar clinical data to that used in their 1991 paper, have suggested a best fit model with four factors: reality distortion (positive symptoms), negative symptoms, disorganization, and premorbid impairment. However, the subtitle of their paper (including "perhaps four") suggests that as far as the structure of schizophrenic symptoms is concerned, the jury are still out. 599

14 Schizophrenia Bulletin, Vol. 26, No. 3, 2000 P.H. Venables and N.A. ector Although in the present study model L presents a quite acceptable solution and thus in isolation could be taken to support a four-dimensional structure, it is intrinsically unsatisfactory because, as has been seen above, positive schizotypy and disorganization are in this population not adequately separable. An argument might be made that this is because the sample studied here is essentially normal and that disorganization would appear as a separate factor in a clinical population. Instances where content and structure change depending on whether measurement is carried out on normal or clinical subjects and/or with different instruments are shown by the comparison of the studies of Bergman et al. (1996) who measured aspects of SPD by clinical interview using SIDP (Structured Interview for DSM Personality Disorders; Pfohl et al. 1982), and a study that used the SPQ (aine 1991). Bergman et al. (1996) arrived at a best fit, three-dimensional structure described as cognitive/perceptual, interpersonal, and paranoid, whereas the best fit solution of aine et al. (1994) was cognitive/perceptual, interpersonal, and disorganized. Bergman et al. (1996) suggest that the discrepancy between the two studies may rest with the type of measurement, that is, interview versus self-report. However, on the other hand, they suggest that the difference may lie in the fact that the aine et al. (1994) study was on an unselected normal population and theirs was on a population with DSM-HI personality disorders. To back up this suggestion they cite osenberger and Miller (1989), who reported a cognitive/perceptual, interpersonal, paranoid structure using very different self-report measures but on a subsample of a normal population selected to be at the abnormal end of the distribution of scores and hence with the likelihood of clinical characteristics. There does not therefore appear to be strong evidence that the results of the present study depend, in a major way, on the characteristics of the population studied. eferences Akaike, H. Factor analysis and AIC. 52: , Psychometrika, American Psychiatric Association. DSM III: Diagnostic and Statistical Manual of Mental Disorders. 3rd ed. Washington, DC: APA, American Psychiatric Association. DSM-IV: Diagnostic and Statistical Manual of Mental Disorders. 4th ed. Washington, DC: APA, Andreasen, N.C. Scale for the Assessment of Negative Symptoms (SANS). Iowa City, IA: University of Iowa, 1984a. Andreasen, N.C. Scale for the Assessment of Positive Symptoms (SAPS). Iowa City, IA: University of Iowa, Andreasen, N.C; Arndt, S.; Miller, D.; Flaum, M.; and Nopoulos, P. Correlational studies of the Scale for the Assessment of Negative Symptoms and the Scale for the Assessment of Positive Symptoms: An overview and update. Psychopathology, 28:7-17,1995. Andreasen, N.C, and Olsen, S. Negative versus positive schizophrenia: Definition and validation. Archives of General Psychiatry, 39: , Bentall,.P.; Claridge, G.S.; and Slade, P.D. The multidimensional nature of schizotypal traits: A factor analytic study with normal subjects. British Journal of Clinical Psychology, 28: ,1989. Bentler, P.M. Comparative fit indices in structural models. Psychological Bulletin, 107: , 1990a. Bentler, P.M. Fit indexes, Lagrange Multipliers, constraint changes and incomplete data in structural models. Multivariate Behavioral esearch, 25: , Bentler, P.M. EQS Structural Equations Program Manual. Encino, CA: Multivariate Software, Bentler, P.M., and Bonett, D.G. Significance tests and goodness of fit in the analysis of covariance structures. Psychological Bulletin, 88: , Bergman, A.J.; Harvey, P.D.; Mitropoulou, V.; Aronson, A.; Marder, D.; Silverman, J.; Trestman,.; and Siever, L.J. The factor structure of schizotypal symptoms in a clinical population. Schizophrenia Bulletin, 22(3): , Bozdogan, H. Model selection and Akaike's Information Criteria (AIC): The general theory and its analytical extensions. Psychometrika, 52: , Byrne, B.M. Structural Equation Modelling with EQS and EQS/Windows. Thousand Oaks, CA: Sage Publications, ' Chapman, J. The early symptoms of schizophrenia. British Journal of Psychiatry, 112: , Chapman, J.P.; Chapman, L.J.; and Kwapil, T.. Scales for the measurement of schizotypy. In: aine, A.; Lencz, T; and Mednick, S.A., eds. Schizotypal Personality. Cambridge, U.K.: Cambridge University Press, pp Chapman, L.J., and Chapman, J.P. The search for symptoms predictive of schizophrenia. Schizophrenia Bulletin, 13(3): , Chapman, L.J.; Chapman, J.P.; Numbers, J.S.; Edell, W.S.; Carpenter, B.N.; and Beckfield, D. Impulsive nonconformity as a trait contributing to the prediction of psychotic-like and schizotypal symptoms. Journal of Nervous and Mental Disease, 172: ,