A confirmatory factor analysis of the revised illness perception questionnaire (IPQ-R) in a cervical screening context

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1 Psychology and Health April, 2005, 20(2): A confirmatory factor analysis of the revised illness perception questionnaire (IPQ-R) in a cervical screening context MARTIN S. HAGGER, & SHEINA ORBELL Department of Psychology, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, United Kingdom (Received 13 November 2003; in final form 4 November 2004) Abstract The purpose of the present study was to test the factorial and discriminant validity of the Revised Illness Perception Questionnaire (IPQ-R), a measure of illness representations based on Leventhal, Meyer and Nerenz s Self-Regulation Theory, in a cervical screening context using confirmatory factor analysis. Six hundred and sixty women, who had attended a colposcopy clinic and were invited to re-attend, completed the IPQ-R. Data were analysed using covariance structure analysis. The adequacy of an a priori confirmatory factor analytic model that included seven dimensions of the cognitive illness representation: identity, timeline-acute/chronic, serious consequences, personal control, treatment control, illness coherence, and causal attributions, and one emotional representation factor was tested against the observed data. After the elimination of two items responsible for large standardised residuals and with low factor loadings, the model adequately accounted for covariances among the IPQ-R items according to multiple criteria for goodness-of-fit. Factor inter-correlations supported the discriminant validity of the constructs and the factors exhibited satisfactory composite reliability. A theoretically predictable pattern of relationships among the representation dimensions was evident. In particular, the control-related constructs and the illness coherence dimension were negatively related to other illness representation constructs. The present study provided confirmatory evidence using a robust hypothesis-testing framework to support the proposed structure of the illness representation dimensions in a cervical screening context. Keywords: Self-regulation theory, common-sense model, illness cognitions, validity, colposcopy Correspondence: Martin S. Hagger, Department of Psychology, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, United Kingdom. hagger@essex.ac.uk ISSN print/issn online ß 2005 Taylor & Francis Group Ltd DOI: /

2 162 M. S. Hagger & S. Orbell Introduction There has been a recent resurgence of interest in Leventhal, Meyer & Nerenz s (1980) self-regulation theory to explain the cognitive antecedents of coping behaviours and illness outcomes in chronic illness (Hagger & Orbell, 2003). This has been coupled with recent advances in self-report measurement instruments designed to tap the key variables associated with illness representations, such as the Illness Perception Questionnaire (IPQ; Weinman, Petrie, Moss-Morris & Horne, 1996) and the Revised Illness Perception Questionnaire (IPQ-R; Moss-Morris et al., 2002). While these instruments are considered the measure of choice in recent studies on selfregulation theory (e.g., Brewer, Chapman, Brownlee & Leventhal, 2002; Hagger, Chatzisarantis, Griffin & Thatcher, in press; Heijmans & De Ridder, 1998; Rutter & Rutter, 2002), none of the studies have provided confirmatory evidence using a latent variable approach to support its proposed structure. The present study aims to provide a rigorous psychometric evaluation of the IPQ-R in a cervical screening context using confirmatory factor analysis. The confirmatory approach offers robust support for hypothesised structures in psychometric inventories because it enables the researcher to specify the arrangement of factors a priori. Such an analysis may yield additional evidence to support the construct and discriminant validity of the proposed arrangement of the IPQ-R dimensions in accordance with theory, and provide some evidence to support the adoption and use of the IPQ-R in a cervical screening context. Self-regulation theory Self-regulation theory proposes that individuals construct schematic representations of illness and health-threatening conditions according to the concrete and abstract sources of information available to them (Leventhal et al., 1980). Health professionals such as general practitioners, nurses, and surgeons can be sources of information as can the general pool of information available from social sources and symptomatic experience with the illness itself (Leventhal, Nerenz & Steele, 1984). Leventhal et al. (1984) proposed that if the individual s representation of the illness is sufficiently threatening, it will evoke a coping response. The appraisal of the effectiveness of the coping procedures adopted may result in the modification and updating of the cognitive representation in a dynamic process (Leventhal, Nerenz & Steele, 1984). Extensive semi-structured interviews, open-ended questionnaire investigations, and factor-analytic studies have established that illness representations are multidimensional and have a common content across illnesses (e.g. Turk, Rudy & Salovey, 1986; Weinman et al., 1996). Factor analytic studies resulted in the development of generic measures of illness representations such as the implicit models of illness questionnaire (IMIQ; Turk et al., 1986) and the IPQ-R (Moss-Morris et al., 2002). These instruments measured illness representations on five related, but conceptually and empirically distinct, components: identity, timeline, cause, serious consequences, and curability/controllability. Although it was assumed that individuals with different illnesses would represent their condition on this same set of dimensions, the structure and levels of the content may differ across illnesses (Heijmans & De Ridder, 1998). The identity component reflects the illness label and perceived symptoms associated with the illness. The timeline dimension refers to a person s beliefs about the relative

3 Confirmatory factor analysis of IPQ-R 163 chronicity of the illness. An individual s attribution of cause of the illness to different factors makes up the cause component, while perceptions of the potential of the illness to have a serious impact on an individual s lifestyle and well-being comprise the serious consequences dimension. The curability/controllability component reflects an individual s assessment as to whether they have the personal resources to control the illness and beliefs in the effectiveness of treatment. These constructs have been corroborated in numerous studies and can be regarded as the core components of illness representations (Hagger & Orbell, 2003; Heijmans & De Ridder, 1998; Weinman et al., 1996). The revised illness perception questionnaire The development of the IPQ-R represented the advancement in theory and measurement of the constructs related to self-regulation theory. Following the success of the original IPQ, Moss-Morris et al. (2002) identified key areas in the core IPQ dimensions that needed revision. It was recognized that the identity component did not account for a person s judgements as to the clarity of meaning of the illness to them and whether it made sense to them personally. As a consequence, the illness coherence scale was introduced to encompass these beliefs. In addition, the content of the original cure/control component from the IPQ was viewed by Horne (1997) as confounding sets of beliefs about personal abilities to control the illness and the efficacy of treatment to cure or manage the illness. These sets of beliefs were therefore treated separately in the revised inventory as the personal control and treatment control scales. Further, the timeline dimension was differentiated into beliefs about the relative chronicity of the illness and beliefs about the fluctuation in symptoms and temporal changeability of the illness. The new scales were labelled timeline-acute/ chronic and timeline-cyclical, respectively. Perhaps the most important revision of the IPQ was the inclusion of a measure of emotional representations in the revised inventory. Leventhal et al. (1984) suggested that individuals form parallel cognitive and emotional representations of health threats, but previous measures had neglected the emotional component. Emotional representations are hypothesized to drive emotion-related coping procedures and are likely to be associated with emotion-related outcomes in a similar manner to the cognitive representation of illness (Hagger & Orbell, 2004). The theory also explicitly states that emotional representations are reciprocally related to the cognitive representations and implicated in the coping and appraisal processes. For this reason, self-regulation theory is also called the parallel processing model. A six-item emotional representations scale was included in the IPQ-R. It was expected that emotional representations would be related to the cognitive components of illness representation, as well as act as an independent predictor of emotion-related coping procedures and outcomes. Moss-Morris et al. (2002) provided evidence to support the validity and reliability of the IPQ-R in a number of chronic and acute conditions. Exploratory factor analysis supported the construct validity of the revised dimensions of timeline-acute/chronic, timeline-cyclical, serious consequences, personal control, treatment control, illness coherence, and emotional representations. Discriminant validity of the resulting scales was confirmed through correlations of the subscales with measures of trait affect. Further, a known-group differences test of discriminant validity showed that patients with acute pain scored lower on all but the control-related constructs than

4 164 M. S. Hagger & S. Orbell patients with chronic. The IPQ-R constructs also exhibited a characteristic and theoretically predictable pattern of inter-relationships. Specifically, the control-related constructs and illness coherence dimension tended to exhibit significant, negative relationships with the other illness representation dimensions, while significant, positive correlations were observed among the timeline-acute/chronic, timeline-cyclical, serious consequences, and emotional representations dimensions. This corroborated and extended the arrangement of inter-correlations among the illness representation dimensions found across studies of chronic illness in a recent meta-analysis (Hagger & Orbell, 2003). The present study Despite the rigour of the analyses offered by Moss-Morris and coworkers in their development of the IPQ-R, we know of no study that has adopted a confirmatory approach to examining the construct validity of the IPQ-R. The promise of the confirmatory factor analytic (CFA) method is that it permits an a priori specification of a factor structure using a hypothesis-testing framework, as opposed to the post hoc labelling of extracted factors that occurs in exploratory factor analysis. Since CFA gives the researcher the ability to make an a priori specification and test its adequacy against observations, it is considered the gold-standard method for the evaluation of construct validity in psychometric inventories (Hu & Bentler, 1999). In addition, the CFA approach enables the measurement error associated with the scales to be explicitly modelled resulting in error free latent variables (Martin, 1982). This is considered superior to constructing scales by averaging or summing observed items, as this practice does not eliminate the random error. CFA also tests the discriminant validity of constructs through the intercorrelations among the latent factors (Bagozzi & Kimmel, 1995). We therefore aim to provide further support for the validity and reliability of the IPQ-R by adopting the CFA approach in the present study. Few studies have examined illness sufferer s representations of asymptomatic conditions such as those associated with pre-cancerous changes on the cervix detected by cervical screening. Cervical screening in the UK is a nationwide scheme run by the National Health Service (NHS) to detect abnormalities in cervical cells that are implicated in subsequent development of cancer later in life (Patnick, 2000). Women who attend for three-yearly smear tests at their general medical practice and receive an abnormal result are referred to a colposcopy clinic where the extent of the abnormality is assessed and, if necessary, treatment or further monitoring provided. Leventhal et al. s (1980) specification of self-regulation theory suggests that health threatening information is a key stimulus that results in the formation of an illness representation. In the context of cervical screening, information such as receiving an abnormal cervical smear result or being informed of the presence of a high grade of abnormal cells on the cervix represents this type of information. The investigation of the structure of illness representations in a cervical screening context is therefore an important pre-requisite step to establish the meaning of health threatening information to patients with cervical abnormalities. In addition, establishing the validity of the IPQ-R in this context may pioneer the use of this instrument and tests of self-regulation theory in other cancer screening contexts (Orbell, Hagger, Brown & Tidy, 2004).

5 Confirmatory factor analysis of IPQ-R 165 The present study aimed to conduct a confirmatory factor analysis of the IPQ-R in a cervical cancer setting. Specifically, patients who were at the second stage of the UK NHS National Cervical Screening Programme and had received an abnormal cervical smear test, had attended their first appointment at the colposcopy clinic, and were invited to re-attend were recruited to the study. Such patients had received health-threatening information in the form of the extent of their cervical abnormality by the clinic consultant based on colposcopic impression. It was hypothesised that the theoretically derived a priori structure of the IPQ-R dimensions of timeline-acute/ chronic, serious consequences, personal control, treatment control, illness coherence, and emotional representations would satisfactorily explain the covariances among the items from IPQ-R responses of the colposcopy patients. It was also expected that the IPQ-R constructs would achieve discriminant validity and be inter-related in accordance with the emergent pattern reported in previous studies. Further, it was anticipated that the constructs would also exhibit satisfactory reliability. Method Participants and procedure Participants were recruited to the study as a part of a larger study examining women s follow-up attendance at colposcopy after receipt of an abnormal cervical smear test. Participants were eligible if they had attended a first appointment at one of the two hospital-based colposcopy clinics following an abnormal cervical smear test as part of the UK NHS National Cervical Screening Programme and had been given a subsequent follow-up appointment. A total of 2471 women were eligible for the study, having received an abnormal cervical smear test result and attended their first appointment at the colposcopy clinic. Of these, 1258 were told that they were being given a second appointment as a result of having sufficient cervical abnormality to warrant monitoring or treatment according to colposcopic impression. These women were recruited to the study and sent a letter explaining the purpose of the study together with a questionnaire containing the study measure to their home address three weeks prior to their follow-up appointment. A total of 660 questionnaires were returned, representing a 52.46% response rate. Demographic data on eligible participants age, area of residence, marital status, and degree of cervical abnormality based on colposcopic impression were gathered from their patient records on the hospital database. Comparing the demographic data for responders and non-responders indicated that responders were more likely to be older (responder s mean age ¼ 35.44, SD ¼ 10.28, non-responders mean age ¼ 34.08, SD ¼ 10.40; F 1,1256 ¼ 5.46, p < 0.05, partial 2 ¼ 0.004), score lower on the Carstairs index of social deprivation (responder s mean Carstairs score ¼ 2.62, SD ¼ 3.67, non-responders mean Carstairs score ¼ 3.40, SD ¼ 3.70; F 1,1256 ¼ 3.75, p < 0.01, partial 2 ¼ 0.011), and were more likely to be married (57.60% of responders were married compared with 42.4% for nonresponders; 2 ¼ 8.40, df ¼ 1, p < 0.01).While these should be acknowledged as evidence for response bias, it must be noted that the effect sizes ( 2 ) for these differences were small. Responders and non-responders were equally likely to receive a result indicating high grade of cervical abnormality.

6 166 M. S. Hagger & S. Orbell Measure The Revised Illness Perception Questionnaire (Moss-Morris et al., 2002) was used to tap the identity, timeline-acute/chronic, serious consequences, personal control, treatment control, illness coherence, emotional representation, and causal attribution dimensions from self-regulation theory. The timeline-cyclical scale was omitted since it was deemed irrelevant to patients who had been diagnosed with a condition that is largely asymptomatic. The IPQ-R was adapted according to the recommendations of Moss-Morris et al. (2002) to make reference to the condition in question; cervical abnormalities. As a consequence, the IPQ-R items began with the stem: The problem with my cervix..., in accordance with the type of information about the condition given to the patient based on the colposcopic impression after their first attendance at the clinic. The items for the timeline-acute/chronic, serious consequences, personal control, treatment control, illness coherence, and emotional representations scales were presented in a mixed order and were rated on sixpoint scales ranging from (1) disagree very strongly to (6) agree very strongly. Although the IPQ-R traditionally adopts a five-point scale format and a fixed order, we felt that the adoption of a scale with no clear mid-point and mixing the order would minimise response bias. The causal attribution scale of the IPQ-R was augmented to include risk factors associated with cervical cancer including sexual intercourse, promiscuity, having children, and warts [HPV] virus (Brinton et al., 1987). While the condition is likely to be asymptomatic, an identity scale was formed for the symptoms relevant to cervical problems. Responses were rated on four-point scales with scale points (1) never, (2) occasionally, (3) frequently, and (4) all the time. The items in this scale were: pain (36.6% of participants reported experiencing this symptom at least occasionally ), soreness (37.6%), discharge (60.9%), discomfort sitting (15.2%), sleep difficulties (23.0%), foul odour (32.9%), bleeding (37.7%), and discomfort during sexual intercourse (44.8%). Data analysis The hypothesised factor structure of the IPQ-R was tested using robust maximum likelihood confirmatory factor analysis (CFA). The hypothesised CFA model estimated in the present study specified the items purported to measure the timelineacute/chronic, identity, serious consequences, personal control, treatment control, illness coherence, causes, and emotional representation constructs as indicators of a latent factor representing their respective theoretical construct. A single indicator (factor loading) was arbitrarily selected to be set at unity to define the scale of the factor. The error term associated with each indicator and the variances of the latent factors were also free parameters in the model. The latent factors were all allowed to covary as is typical in CFA models (Bentler, 1995). The adequacy of the proposed CFA model to account for the observed covariance matrix is usually evaluated using the goodness-of-fit chi-square ( 2 ). However, given the sensitivity of the 2 to sample size, it is considered an over-stringent criterion (Bentler, 1990). As a consequence, incremental indices of good-fit, the Comparative Fit Index (CFI) and Non-Normed Fit Index (NNFI), were used to evaluate the adequacy of the models. These indices provide a reliable evaluation

7 Confirmatory factor analysis of IPQ-R 167 of goodness-of-fit because simulation studies have shown that they are least influenced by sample size (Fan, Thompson & Wang, 1999). The indices should exceed 0.90 for an acceptable fit (Bentler, 1990), although values approaching 0.95 are considered preferable (Hu & Bentler, 1999). In addition, the Root Mean Square Error of Approximation (RMSEA) was also used as further index of good-fit, and values close to or below 0.05 were considered acceptable (Hu & Bentler, 1999). In addition to the overall evaluation of good fit, we examined the solution estimates to provide a complete assessment of model adequacy (Bollen, 1989). The standardised factor loadings and standardised residuals were examined to identify areas of misspecification and possible candidates for model modification. In cases of model modification, Akaike s Information Criterion (AIC) was used to compare models, rather than the likelihood ratio ( 2 ) test because the modified models are not nested models (Marcoulides & Hershberger, 1997). As there is no criterion value for the AIC, the model that obtained the lowest value was favoured. Reliability of the latent factors was estimated using composite reliability estimates and discriminant validity of the IPQ-R constructs was assessed by examining the correlations among the latent factors (Bagozzi & Kimmel, 1995). To achieve discriminant validity, the difference between unity and the value of the correlation should exceed 1.96 multiplied by the standard error of the correlation (Bagozzi & Kimmel, 1995). Results The hypothesised CFA model included six indicators each for the timeline-acute/ chronic, serious consequences, personal control, and emotional representation constructs, five indicators for the treatment control and illness coherence factors, and eight indicators for the identity factor. The causal attribution scale was treated differently as it has been recommended that this scale is examined in an exploratory fashion in the first instance to identify groups of causal beliefs (Hagger et al., in press; Moss-Morris et al., 2002; Weinman, Petrie, Sharpe & Walker, 2000). An exploratory factor analysis of the 22 cause items was therefore conducted using a principal components analysis followed by an oblimin rotation of the extracted factors. Eight of the cause items were eliminated from the analysis because they exhibited low factor loadings or loaded highly on more than one factor. The factor analysis was recalculated after the elimination of these items. Three factors were extracted that explained 60.49% of the variance among the cause items. The rotated factor solution is given in Table I. A content analysis of the items comprising each factor resulted in the assignment of the following labels: psychological stress cause, sexual/biological cause, and behavioural cause, in keeping with other research using the cause scale (Hagger & Orbell, 2004; Heijmans & De Ridder, 1998; Orbell, Haggar, Brown & Tidy, 2004). In order to keep the number of parameters in the CFA to a manageable size, we parcelled the items from each factor unveiled in the exploratory analysis and used these as indicators of latent causal attribution factor in the CFA. Previous research has supported this procedure provided there is adequate theoretical basis for the production of the parcels and an a priori CFA with a higher order factor describing the covariances among latent variables of the indicators to be parcelled exhibits adequate fit with the data (Kim & Hagtvet, 2003). The initial hypothesised CFA model reproduced the observed covariance matrix adequately according to the multiple criteria for goodness-of-fit adopted

8 168 M. S. Hagger & S. Orbell Table I. Factor loadings for the exploratory factor analysis of IPQ-R cause items. Factor Item Psychological stress Sexual/biological Behavioural Stress or worry Family problems or worries My emotional state Overwork My mental attitude Diet or eating habits Sexual intercourse My own behavior Warts (HPV) virus Germ or virus Accident or injury Smoking Alcohol Having children Note: Highest factor loadings in bold typeface. (CFI ¼ 0.911; NNFI ¼ 0.904; RMSEA ¼ 0.042). However, some factor loadings had values below the permissible minimum of 0.40 advocated in factor analysis (Ford, MacCallum & Tait, 1986) and multiple large standardised residuals were evident for some of the items. We therefore modified the model using an iterative process in which items contributing most to model misspecification were removed individually in a systematic fashion (Bollen, 1989). Items were removed on the basis of their being associated with multiple large standardised residuals and their factor loading. In addition, criteria for face validity such as degree of redundancy and relevance of the items were also used alongside the statistical criteria as a means for item removal. After the removal of each item, the model was re-estimated and the solution estimates re-examined until there were no items with multiple large standardised residuals. Models were compared using the AIC as well as subjective comparisons of the goodness-of-fit indices. This process resulted in items 9 ( The problem with my cervix strongly affects the way others see me ) and 10 ( The problem with my cervix has serious financial consequences ) being eliminated. The content of these items was not considered relevant to the asymptomatic nature of cervical abnormalities. The final model exhibited superior goodness-of-fit statistics (CFI ¼ 0.926; NNFI ¼ 0.920; RMSEA ¼ 0.040), few large standardised residuals, and acceptable levels for factor loadings. Changes in response format and order of the variables in the present study did not appear to affect the integrity of the model. The factor loadings and error variances of each item from the final CFA model are given in Table II. Composite reliability coefficients for each latent factor are also given in Table II and the coefficients exceeded the recommended minimum of 0.60 in all cases (Bagozzi & Kimmel, 1995). Factor correlations for the final CFA model of the IPQ-R are given in Table III. While there were strong and significant correlations among many of the IPQ-R constructs, all were significantly different from unity (Bagozzi & Kimmel, 1995). The factor correlations also corroborated the pattern observed among illness representation dimensions observed in previous studies (Hagger & Orbell, 2003; Moss-Morris et al., 2002; Weinman et al., 1996). Significant, positive correlations were observed

9 Table II. Standardised factor loadings, standard errors, and composite reliabilities of IPQ-R factor indicators. Factor, item number and item description SE Factor, item number and item description SE Identity ( ¼ 0.816) IPQ4...will pass quickly Pain IPQ5...will last for the rest of my life Soreness IPQ18...will improve in time Vaginal discharge Serious consequences ( ¼ 0.862) Discomfort sitting IPQ6...is a serious condition Sleep difficulties IPQ7...has major consequences on my life Foul odour IPQ8...does not have much effect on my life Bleeding IPQ9...strongly affects the way other see me Discomfort during sexual intercourse Personal control ( ¼.736) Timeline-acute/chronic ( ¼ 0.909) IPQ12 There is a lot I can do to control IPQ1... will last a short time IPQ13 What I do can determine whether gets better or worse IPQ2... is likely to be permanent rather than temporary IPQ14 The course of... depends on me IPQ3... will last a long time IPQ15 Nothing I do will affect IPQ16 I have the power to influence IPQ28 I have a clear picture or understanding of IPQ17 My actions will have no effect on the outcome of Emotional representations ( ¼ 0.877) Treatment Control ( ¼ 0.829) IPQ33 I get depressed when I think about IPQ19 There is very little that can be done to improve IPQ34 When I think about...i get upset IPQ20 Treatment will be effective in treating IPQ35...makes me feel angry IPQ21 The negative effects of...can be prevented (avoided) by treatment IPQ36...does not worry me IPQ22 Treatment can control IPQ37...makes me feel anxious IPQ23 There is nothing that can help IPQ38...makes me feel afraid Illness coherence ( ¼ 0.868) Causal attributions ( ¼ 0.701) IPQ24... is puzzling to me Psychological stress cause IPQ25... is a mystery to me Sexual/Biological cause IPQ26 I don t understand Behavioural cause IPQ27... doesn t make any sense to me Note. ¼ Standardised factor loading; SE ¼ standard error of factor loading; ¼ composite reliability estimate. Confirmatory factor analysis of IPQ-R 169

10 170 M. S. Hagger & S. Orbell Table III. Factor correlations and composite scale reliabilities among IPQ-R latent factors. Factor Identity 2. Timeline-acute/chronic 0.261** 3. Serious consequences 0.416** 0.577** 4. Personal control * Treatment control 0.173** 0.605** 0.224** 0.216** 6. Illness coherence 0.117* 0.159** 0.228** 0.137** 0.222** 7. Emotional representations 0.303** 0.380** 0.820** ** 0.399** 8. Causal attributions 0.185** 0.245** 0.285** 0.106* 0.372** 0.262** 0.291** * p < 0.05, ** p < 0.01 among the identity, timeline-acute/chronic, serious consequences, emotional representation, and causal attribution constructs. Analogously, significant and positive correlations were apparent among the personal control, treatment control, and illness coherence constructs. Personal control exhibited significant and negative correlations with timeline-acute/chronic, but was not related to the identity, serious consequences, and emotional representation dimensions. Treatment control and illness coherence were significantly and negatively related to the identity, timeline-acute/chronic, serious consequences, emotional representation, and causal attribution dimensions. This arrangement of relationships is in keeping with the hypothesised pattern of relations among these constructs and the arrangement observed in previous studies (Moss-Morris, Petrie & Weinman, 1996). Discussion The purpose of the present study was to conduct a CFA of the IPQ-R in a cervical screening context. After the systematic elimination of two items responsible for misspecification in the model using strict statistical criteria and content evaluation, a revised CFA model exhibited acceptable fit with the IPQ-R data from colposcopy patients. Intercorrelations among the latent factors supported the discriminant validity of the components and corroborated the theoretically derived pattern of correlations among the constructs observed elsewhere (Hagger & Orbell, 2003). The CFA of the IPQ-R also yielded satisfactory composite reliability coefficients supporting the internal consistency of the scales. The present study is unique in that it applies the rigorous, a priori CFA approach to the evaluation of the construct and discriminant validity of the IPQ-R. Other than the development article presented by Moss-Morris and coworkers (2002), few researchers have sought to provide factor analytic evidence to support the use of the IPQ (Heijmans & De Ridder, 1998) and IPQ-R (Hagger et al., in press), and none have applied the confirmatory approach to the IPQ-R. Considering the satisfactory indices of overall fit and solution estimates in the present analysis, there were few misspecifications in the model. Only two items were inappropriate in accounting for variance in the serious consequences construct, perhaps because they focus on a person s perceptions of others evaluations and financial consequences that are not likely to have a serious impact on the participants life. It is recommended that these items be scrutinised carefully when adopting this inventory with other illnesses, and that

11 Confirmatory factor analysis of IPQ-R 171 they be omitted in research in a cervical screening context. Otherwise, the other illness representation dimensions appear to have an optimal structure in this context. This vindicates the rigorous validity approaches used in the development of the IPQ-R and suggests that the IPQ-R is a valid instrument for use in this context. The inter-correlations among the latent factors of the IPQ-R support the discriminant validity of the illness representation constructs and an emergent pattern of relationships among these dimensions. The correlations among the constructs were all significantly different from unity. Strong and statistically significant correlations were observed between the serious consequences and emotional representation dimensions ( ¼ 0.820), and also between timeline-acute/chronic and treatment control constructs ( ¼ 0.605). While these relationships are indicative of a significant degree of shared variance between these constructs, it is clear that they are empirically distinct. It does, however, suggest that the emotional representation construct has strong relationships with a key cognitive representation construct, serious consequences, a finding that is in keeping with Leventhal et al. s (1997) notion that there may be conceptual overlap between the cognitive and emotional components of the model. In addition, the pattern of relationships among the IPQ-R dimensions match the pattern derived for chronic illnesses in Moss-Morris et al. s (2002) original development study and in Hagger and Orbell s (2003) meta-analytic findings with the IPQ and similar measures. This arrangement lends support to the validity of the hypothesis that the organisation of the illness representations is similar across illness and may be schematic in nature. The present study showed that the treatment and personal control constructs were negatively related to the identity, timeline-acute/chronic, serious consequences, and emotional representation constructs. However, the correlations were consistently greater for the treatment control dimension, such that women s perceptions of the chronicity, seriousness, and emotional salience of their condition were more strongly tied with perceptions that the condition is treatable, rather than perceptions that they have control over the illness outcome. This is not surprising in the case of cervical screening as women only have personal control over the treatment of their cervical abnormalities to the extent that they attend their colposcopy appointments (Orbell et al., 2004). Treatment and the degree of treatability of the problem itself are controlled by clinicians at the colposcopy clinic. The strength of the present study is its adoption of a robust, hypothesis-testing framework to provide further empirical support for the IPQ-R. The establishment of a robust structure of the IPQ-R in a cervical screening context is an important pre-requisite step before further studies of the role of illness representations and the self-regulation model are conducted this area. While it would be inappropriate to generalise, the present study may also pave the way for the examination of the factor structure of the IPQ-R in other cancer screening contexts. One limitation of the present study is that the factor structure has not been cross-validated in other samples. Replicating the structure and testing its invariance across samples will provide further evidence to support the arrangement of the IPQ-R factors in this context. In addition, future studies will also replicate the proposed structure of the IPQ-R in other chronic, asymptomatic illnesses. Indeed, a desirable study design would be to test the invariance of the factor structure of the IPQ-R across a number of illnesses with similar symptoms, chronicity, and aetiology. This would corroborate previous

12 172 M. S. Hagger & S. Orbell research which suggests that the structure of illness representations is generalisable across similar illness types (Hagger & Orbell, 2003). Acknowledgement This research was supported by Cancer Research UK grant CP1048/0101. We thank John Tidy, Val Brown, and Janet Williams for their involvement with the study. References Bagozzi, R. P., & Kimmel, S. K. (1995). A comparison of leading theories for the prediction of goal directed behaviours. British Journal of Social Psychology, 34, Bentler, P. M. (1990). Comparative fit indexes in structural models. Psychological Bulletin, 107, Bentler, P. M. (1995). EQS structural equations program manual. Encino, CA: Multivariate Software Inc. Bollen, K. A. (1989). Structural equations with latent variables. New York: Wiley. Brewer, N. T., Chapman, G. B., Brownlee, S., & Leventhal, E. (2002). Cholesterol control, medication adherence and illness cognition. British Journal of Health Psychology, 7, Brinton, L. A., Hamman, R. F., Huggins, G. R., Lehman, H. F., L., Levine, R. S., Mallin, K., & Fraumeni, J. F. (1987). Sexual and reproductive risk factors for invasive squamous cell cervical cancer. Journal of the National Cancer Institute, 79, Fan, X., Thompson, B., & Wang, L. (1999). The effects of sample size, estimation methods, and model specification on SEM fit indices. Structural Equation Modeling, 6, Ford, J., MacCallum, R., & Tait, M. (1986). The application of factor analysis in psychology: A critical review and analysis. Personnel Psychology, 39, Hagger, M. S., Chatzisarantis, N., Griffin, M., & Thatcher, J. (in press). Injury representations, coping, emotions, and functional outcomes in athletes with sport-related injuries: A test of self-regulation theory. Journal of Applied Social Psychology. Hagger, M. S., & Orbell, S. (2003). A meta-analytic review of the common-sense model of illness representations. Psychology and Health, 18, Hagger, M. S., & Orbell, S. (2004). Illness representations and emotion in people with abnormal screening results. Manuscript submitted for publication. Heijmans, M., & De Ridder, D. (1998). Assessing illness representations of chronic illness: Explorations of their disease-specific nature. Journal of Behavioral Medicine, 21, Horne, R. (1997). Representations of medication and treatment: Advances in theory and measurement. In K. J. Petrie, & J. A. Weinman (Eds), Perceptions of health and Illness. London: Harwood Academic Publishers. Hu, L., & Bentler, P. M. (1999). Cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives. Structural Equation Modeling, 6, Kim, S., & Hagtvet, K. A. (2003). The impact of misspecified item parceling on representing latent variables in covariance structure modeling: A simulation study. Structural Equation Modeling, 10, Leventhal, H., Benyamini, Y., Brownlee, S., Diefenbach, M. A., Leventhal, E. A., Patrick-Miller, L., & Robitaille, C. (1997). Illness representations: Theoretical foundations. In K. J. Petrie, & J. Weinman (Eds.), Perceptions of health and illness: Current research and applications (pp ). Amsterdam: Harwood Academic Publishers. Leventhal, H., Meyer, D., & Nerenz, D. (1980). The common sense model of illness danger. In S. Rachman (Ed.), Medical psychology (Vol. II, pp. 7 30). New York: Pergamon Press. Leventhal, H., Nerenz, D. R., & Steele, D. J. (1984). Illness representations and coping with health threats. In A. Baum, S. E. Taylor, & J. E. Singer (Eds), Handbook of psychology and health: Social psychological aspects of health (Vol. 4, pp ). Hillsdale, NJ: Earlbaum. Marcoulides, G. A., & Hershberger, S. L. (1997). Multivariate statistical methods: A first course. Hillsdale, NJ: Erlbaum. Martin, J. A. (1982). Application of structural modelling with latent variables to adolescent drug usage: A reply to Huba, Wingard & Bentler. Journal of Personality and Social Psychology, 43, Moss-Morris, R., Petrie, K., & Weinman, J. (1996). Functioning in chronic fatigue syndrome: Do illness perceptions play a regulatory role. British Journal of Health Psychology, 1, Moss-Morris, R., Weinman, J., Petrie, K. J., Horne, R., Cameron, L. D., & Buick, L. (2002). The revised illness perception questionnaire (IPQ-R). Psychology and Health, 17, 1 16.

13 Confirmatory factor analysis of IPQ-R 173 Orbell, S., Hagger, M. S., Brown, V., & Tidy, J. (2004). Conceptualizing and predicting attendance/ non-attendance for treatment after abnormal screening results: Coping response or planned behavior? Manuscript submitted for publication. Patnick, J., (2000). Cervical cancer screening in England. European Journal of Cancer, 36(2), Rutter, C. L., & Rutter, D. R. (2002). Illness representation, coping and outcome in irritable bowel syndrome (IBS). British Journal of Health Psychology, 7, Turk, D. C., Rudy, T. E., & Salovey, P. (1986). Implicit models of illness. Journal of Behavioral Medicine, 9, Weinman, J., Petrie, K. J., Moss-Morris, R., & Horne, R. (1996). The Illness Perception Questionnaire: A new method for assessing the cognitive representation of illness. Psychology and Health, 11, Weinman, J., Petrie, K. J., Sharpe, N., & Walker, S. (2000). Causal attributions in patients and spouses following first-time myocardial infarction and subsequent lifestyle changes. British Journal of Health Psychology, 5,