What Is the Mechanism by Which Suicide Attempts Predispose to Later Suicide Attempts? A Mathematical Model

Transcription

1 Journal of Abnormal Psychology 989, Vol. 98, o.,-9 Copyright 989 by the American Psychological Association, Inc. l-8x/89/$.7 What Is the Mechanism by Which Suicide Attempts Predispose to Later Suicide Attempts? A Mathematical Model David C. Clark, Robert D. Gibbons, Jan Fawcett, and William A. Scheftner Center for Suicide Research and Prevention, Department of Psychiatry Rush-Presbyterian-St. Luke's Medical Center, Chicago, Illinois A state dependence model of serial behavior suggests that each occurrence increases the subsequent likelihood of that behavior being repeated. A heterogeneity model, by contrast, suggests that the likelihood of a behavior occurring is predetermined, and uninfluenced by intervening occurrences. We have applied the random-effects probit model of Gibbons and Bock (987) to examine the fit of the state dependence and heterogeneity models to longitudinal data on suicide attempts by 98 patients with affective disorder. Heterogeneity but not state dependence was required to model these data. The findings suggest that when considering patients with moderate to severe major affective disorder, the clinician should not interpret the absence of any recent suicide attempts to mean that the patient is at relatively low risk for attempting suicide in the future. An implication of the heterogeneity model is that suicide attempts made many years ago may have equal value to recent attempts when estimating an individual's "predisposition" to nonlethal attempts in the future. A history of nonlethal suicide attempts is associated with a higher risk for subsequent nonlethal attempts (Buglass & Horton, 97; Clayton, 98; Morgan, Barton, Pottle, Pocock, & Burns-Cox, 976; Siani, Garzotto, Zimmerman-Tansella, & Tansella, 979), but the mechanism that might explain this association has received scant attention. One may hypothesize, for example, that a history of suicide attempts is the emblem of an individual predisposed to manifest suicidal behavior by vir- These data were collected for the ational Institute of Mental Health-Clinical Research Branch, Collaborative Program on the Psychobiology of Depression: Clinical Studies. This study was completed with the cooperation and participation of the following collaborative investigators: G. L. (German (Chairperson; ew \brk), R. M. A. Hirschfeld (Project Director and Cochairperson), and Pamela Griffith (Washington, DC); M. B. Keller and P. Lavori (Boston); J. Fawcett and W. A. Scheftner (Chicago);. C. Andreasen, W. Coryell, G. Winokur, and P. Wasek (Iowa City); J. Endicott, P. McDonald-Scott, and J. E. Loth (ew York); J. Rice, T. Reich, and D. Altis (St. Louis). Other contributors include P. J. Clayton, M. M. Katz, E. Robins, R. W. Shapiro, and R. Spitzer. This analysis was supported by Chicago site ational Institute of Mental Health Grant U MH997-. This article was reviewed and endorsed by the Publications Committee of the Collaborative Depression Study. An earlier version of this article was presented at the Invitational Conference on Applications of Quantitative Analytic Methods to Mental Health: Practice, Policy, and Research, cosponsored by the Institute for Health Research of the Harvard Community Health Plan and Harvard University, and the ational Institute of Mental Health, in Boston, April -, 987. The authors are indebted to James H. Ware, Harvard School of Public Health, and Lee. Robins, Washington University School of Medicine, for thoughtful criticisms and comments. Robert D. Gibbons is now at the Departments of Biometry and Psychiatry, University of Illinois. Correspondence concerning this article should be addressed to David C. Clark, Center for Suicide Research and Prevention, 7 West Polk Street, Chicago, Illinois 66. tue of some latent person-specific trait: for example, a genetic predisposition, a psychophysiological anomaly, a personality disorder, or a developmental vulnerability. This hypothesis might be designated the trait hypothesis. Alternatively, one may hypothesize that the etiology of a first suicide attempt is a much less predetermined, much more situational or fortuitous event; but that once a person makes a suicide attempt, some psychological threshold is lowered, so that the likelihood of a subsequent attempt increases with every new attempt. This second hypothesis might be designated the crescendo hypothesis. And finally, the two hypotheses are not mutually exclusive or exhaustive; both may be true simultaneously (the interaction hypothesis), or neither may be true. Until recently, there were no mathematical models for testing or comparing these hypotheses. But the work of Heckman and Borjas (979) and Heckman (98) in the field of econometrics introduced a new strategy for testing state-dependent relations (i.e., the crescendo hypothesis). Subsequently, Gibbons and Bock (987) extended the work of Heckman and Borjas by developing a random-effects probit model capable of testing for the presence of both the state dependence and heterogeneity (i.e., the trait hypothesis) models and their interaction. We have applied the random-effects probit model of Gibbons and Bock to analyze longitudinal data on the suicidal behavior of 98 psychiatric patients at five different geographical centers who were originally interviewed with the Schedule for Affective Disorders and Schizophrenia (SADS; Endicott & Spitzer, 978) and met Research Diagnostic Criteria (RDC; Spitzer, Endicott, & Robins, 978) for a major or chronic minor affective disorder. Our objective was to determine whether data on the incidence of suicide attempts during the baseline and -year follow-up interval support the trait hypothesis, the crescendo hypothesis, both, or neither. Method Subjects The Clinical Studies of the ational Institute of Mental Health-Clinical Research Branch Collaborative Program on the Psychobiology of

2 MECHAISM UDERLYIG RECURRET SUICIDE ATTEMPTS Depression were conducted at hospitals associated with five academic centers: Harvard Medical School in Boston, Rush-Presbyterian-St. Luke's Medical Center in Chicago, University of Iowa in Iowa City, ew York State Psychiatric Institute in ew York City, and Washington University School of Medicine in St. Louis. The intent and design of the overall study have been described in detail elsewhere (Katz & KJerman, 979). Consenting inpatients and outpatients were included if they met RDC criteria for definite major depression, manic disorder, schizoaffective disorder, or chronic intermittent depressive disorder. Patients were seeking psychiatric treatment through customary referral mechanisms for those institutions. Subjects were required to be at least 7 years old, Caucasian, and fluent in English; to possess an IQ above 7; to show no evidence of acute or chronic brain syndrome; and to have knowledge of their biological parents. A total of 9 patients were admitted to the study by these criteria; 8 were inpatients. Five hundred fifty-two subjects (8) were women. Of the total sample, 9 patients () were between 7 and 8 years old, (6) were between 9 and years old, and 9 () were between and 79 years old (M = 8. years, SD =.). When patients were categorized by educational level, 6 () had completed graduate professional training, () had completed college, 9 (8) had graduated from high school, and only (6) had not completed th grade. By excluding 7 patients who died during the first years of followup (including 6 patients who died by suicide), we reduced the sample size to 98 for the present analysis. Patients who died were excluded for two reasons: (a) we did not want to equate completed suicide with nonlethal attempts (Stengel, 96; Schmidt, O'eal, & Robins, 9), choosing to focus on the latter; and (b) the suicidal behavior of patients who died during the follow-up period could not be quantified after death in a manner consistent with the behavior of surviving subjects. To examine the impact of this decision on our results, we will also examine the association between nonlethal suicide attempts and death by suicide in the context of our model in the Results section. Initial Assessment Inpatients were contacted as soon as possible after admission to the hospital, which was usually within several days; outpatients were contacted during the first few intake sessions. The current psychopathology and lifetime psychiatric history of subjects were assessed by trained clinical raters using the SADS-RDC instruments. The SADS ratings were based on a compilation of data from patient interviews, contact with significant others, and psychiatric records, and not based solely on patient self-report. Considerable efforts were made to ensure intercenter and intracenter reliability of the clinical ratings; the high levels of interrater reliability have previously been reported (Andreasen et al.,98; Keller et al., 98 la; Keller et al., 98 Ib). A breakdown of the sample by RDC diagnosis appears in Table. On completion of the SADS- RDC interviews, subjects participated in a variety of other interviews concerning their sociodemographic backgrounds, family history, medical history, social support systems, recent life events, and personality. Follow- Up Assessments Exhaustive attempts were made to contact and re-interview every subject with several structured interviews (the Longitudinal Interval Follow-Up Evaluation [Keller et al., 987], the ew Episode/Condition Report, and the Suicide Attempt Death Report) at 6-month intervals for years from the date of study admission. At each follow-up point, the status of at least 96 of the total sample could be determined. Determination of "death" and "death by suicide" outcomes were based on information from family members, clinicians familiar with the patient, and coroners' reports. Treatment decisions were in the hands of the variety of attending psychiatrists and house officers caring for these patients (independent of the research protocol), and thus varied from center to Table Sample Description Using Research Diagnostic Criteria Description Ever schizoaffective Ever alcoholic Ever drug abuse/dependence Currently schizoaffective Currently alcoholic Currently drug abuse/dependence Currently manic Cycling episode, Bipolar Manic episode, Bipolar Unipolar manic Currently depressed Cycling episode, Bipolar Cycling episode, Bipolar Recurrent unipolar, primary Recurrent unipolar, secondary First episode, primary Psychotic subtype Incapacitated subtype Endogenous subtype Agitated subtype Retarded subtype Situational subtype Probable W Definite ote. = 9. For Drug abuse/dependence, Probable score denotes drug abuse, and Definite score denotes drug dependence. center and patient to patient, but were systematically recorded during the follow-up. Defining and Quantifying Attempts Using SADS item definitions (Endicott & Spitzer, 978) pertaining to suicidal behavior (ideas, gestures, or attempts), we interpreted any example of suicidal behavior associated with an intent tonality rating of or greater (i.e., definite but very ambivalent), or with a medical lethality rating of or greater (i.e., took aspirins and developed mild gastritis), as a suicide attempt. A clear intention to die or an overt suicidal act was required by this definition. Each of five time periods (current episode for no longer than months up to and including initial assessment, and four 6-month followup intervals) was then characterized with a single dichotomous score (the presence or absence of any suicide attempts), so the string of five dichotomous scores could be used to describe the suicidal behavior of each subject over time. In this way the sequential behavior of each subject could be examined and analyzed quantitatively. Past suicide attempts (i.e., those predating the initial assessment by more than year) were not examined because of evidence that three fourths of a large sample cannot recall their own depressive episodes after to years, and that individuals alter their reports of past psychological disorder as a function of their current mood state (Aneshensel, Estrada, Hansell, & Clark, 987). State Dependence and Heterogeneity Models The concepts of state dependence (the crescendo hypothesis) and heterogeneity (the trait hypothesis) may be illustrated with reference to two phenomena other than suicide attempts: unemployment and accident proneness. The state dependence model of unemployment takes the position that

3 CLARK, GIBBOS, FAWCETT, AD SCHEFTER periods of unemployment may directly affect the worker's chances of experiencing unemployment in the future. Workers of identical productivity but different employment experience may be evaluated differently by hiring employers, for example, if a period of unemployment causes the worker to lose valuable work experience, lose opportunities for updating skills on the job, or if employers have no other reliable way to judge the ability of potential employees. A state dependence model may hypothesize that the fact of unemployment, or the number of episodes of unemployment, or the duration of unemployment increase future likelihood of unemployment. The heterogeneity model of unemployment takes the position that some individuals (because of ability, attitude, personality, or psychopathology) are less productive and therefore less employable than others from the first day of work. In this case knowledge that an individual has been unemployed is valid information for assessing his true ability or productivity. The fact of unemployment, the number of episodes of unemployment, or the duration of unemployment may provide some general index of the worker's ability or productivity, but none directly affect his future chances of becoming unemployed. The heterogeneity model predicts that the association between past and future unemployment would disappear if individual differences in ability or productivity could somehow be controlled. In other words, the heterogeneity model predicts that for each individual, unemployment risk is predetermined, and uninfluenced by intervening episodes of unemployment. The two models can also be applied to the phenomenon of "accident proneness." The state dependence model takes the position that something inherent to the occurrence of an accident may promote recurrences, so that the risk of a subsequent accident rises with each new accident. For example, a prior accident may diminish an individual's concentration, or cause the individual to exercise overcompensatory caution, for a defined period of time. The heterogeneity model, on the other hand, takes the position that the number of accidents experienced by an individual over time reflects the severity of his or her "predisposition" to accidents. Thus, a single accident is a direct indicator of the underlying predisposition but does not directly affect the likelihood of having another accident. To return from analogies to suicide attempts, the state dependence model (crescendo hypothesis) suggests that the very occurrence of an attempt increases subsequent risk for another attempt by some unspecified mechanism: for example, by increasing a self-destructive urge, lowering a self-protective or impulse-delaying threshold, undermining selfconfidence, or causing others (family, friends, employer, or therapist) to treat the individual differently. The heterogeneity model (trait hypothesis), by comparison, suggests that the number of attempts made by an individual over time are less a reaction to previous attempts and more the expression of some fundamental underlying process. The heterogeneity model suggests that the number of attempts reflects some innate predisposition, which might be defined in terms of genetics, biology, or character development. Gibbons and Bock (987) have presented a statistical model for estimating trends in correlated proportions that can be used to directly test the hypotheses of state dependence and heterogeneity. (See the article for a detailed development of the model, method of parameter estimation, and hypothesis testing.) Briefly, the model assumes that each individual follows an unobservable straight-line regression over time. On occasion k, a given individual will make a suicide attempt, coded x k =, if the value of his unobservable "response strength" or "suicidal tendency" y ik exceeds a threshold y; otherwise the attempt does not occur and is coded x k = o. The unobservable trend line for "suicidal tendency" is where y ik = the unobservable suicidal tendency for patient / on occasion k; a, = the intercept for patient i at / = ; ft = the slope for patient i; fik = pfit-t + «,*; p ~ a first-order autocorrelation parameter that describes the dependence of future deviations from the patient's trend line on previous deviations, that is, state dependence; and t lk = an independent residual distributed.v(,<r ). Assuming equally spaced points recorded as t k = k, k =,,..., n - I and that the distribution of a and j8 is bivariate normal,./vgx,) with. _ and = fi] \, \ the term M«describes the average intercept (i.e., average suicidal tendency at baseline t k = o), and the term MB is the average trend of suicidal tendency over time. The covariance matrix contains information regarding the variability of intercerpts (a a ) and the variability of slopes Op ) in the population, as well as the covariance (<r«), which is the covariance between a and ft In terms of suicidal tendency, a^ describes the relation between where you start and where you end up. Of course, we can never truly measure suicidal tendency (y ik ) but must infer its value from the pattern of suicide attempts over time, which we can observe (i.e., x\, jc,...,x n ). Assuming for the moment that p = (i.e., there is no state dependence), we can obtain the probability that for patient /', x k = I, conditional on «/ and ft as: where P(x k = a, ( = -z k z t = (a + t k -y)/a. Without loss of generality, we may take y = and a =, such that and Using this model, Gibbons and Bock (987) showed how to obtain maximum likelihood estimates (MLEs) of fi a, n a, a a, a^, a f, and p. Comparison of models in which p is constrained to be zero versus the case in which p is replaced by its MLE ~p constitutes a comparison of simple heterogeneity and heterogeneity plus state dependence. A model in which a a, a ai, and tr/ are set to zero and M«, /»/»> and P are estimated constitutes a purely state dependent model. Gibbons and Bock described a likelihood ratio chi-square statistic for the statistical comparison of these three alternative models. In the present study there were s or possible unique response patterns (i.e., the presence or absence of a suicide attempt on each of five occasions). Therefore, the state dependence model, which has three parameters, has = 8 degrees of freedom; the heterogeneity model, which has five parameters, has 6 degrees of freedom; and the combined model, which has six parameters, has degrees of freedom. Gibbons and Bock pointed out that the required sample size for this model is on the order of ( ). For n =, a sample size of is required. The sample used in this article is therefore more than adequate. Results Attempts Coded Dichotomously Table summarizes the frequencies for all the observed patterns of sequential suicidal behavior coded dichotomously for the sample. Among the patients exhibiting no suicidal behavior during the baseline period (=l\6), 6 patients (9 ) made no suicide attempts during the -year follow-up interval; and among the patients who made one or more suicide attempts

4 MECHAISM UDERLYIG RECURRET SUICIDE ATTEMPTS Table Frequency ofdichotomous Patterns of Sequential Suicidal Behavior Patterns ote. = Total Men Women during the baseline period ( = ), patients (7) made no suicide attempts during the same follow-up interval. Thus, a history of one or more suicide attempts during the baseline period was significantly associated with a greater likelihood of attempts during the -year follow-up period, x ) =., p=.. To examine the mechanism underlying this association, we fit the observed data to the three proposed models. The simple state dependence model of suicide attempts was associated with a chi-square statistic of 9.8 on 8 degrees of freedom (p =.), with p =.88. The simple heterogeneity model was associated with a chi-square statistic of 7.9 on 6 degrees of freedom (p =.). The combined model was associated with a chi-square statistic of 7. on degrees of freedom (p =.), with p =.. Thus, the observed data showed an extremely poor fit to the state dependence model, and a good fit to the heterogeneity and combined state dependence and heterogeneity models. The combined model did not provide a significant improvement of fit over the simple heterogeneity model, x ( = -, ns. We therefore conclude that state dependence is not required to model these data. The average trend over time ( ) for the combined model was -.. Because the ratio of the variable to its standard error (.) was much larger than :, we may conclude that the trend was a significant one. The large negative group trend reflects the fact that patients were much more likely to evidence a suicide attempt during the baseline rather than any of the follow-up periods. This step effect, which the model must represent linearly, is evident in the incidence rates portrayed in Table. Comparison of Men and Women by Dichotomous Pattern In an attempt to determine if the mechanism by which suicide attempts predispose to later suicide attempts is the same in men and women, the heterogeneity and state dependence models were fit separately to the suicide attempt patterns for men and women. The distinct response pattern frequencies are listed in Table. In terms of model fit, the overall result was supported in that the combined heterogeneity and state dependence model did not provide a significant improvement in fit over the single heterogeneity model for men, x (l) =.8, ns, p =., or for women, x ( ) = -9, ns, p =.. The only difference was a more rapid decrease in suicide attempts over time for men (p f = -.) relative to women (^ = -.7). Attempts Coded Polychotomously It might be argued that by reducing the actual number of suicide attempts occurring during each assessment interval to a dichotomous score, valuable or even crucial clinical information is sacrificed. Although we cannot model the state dependence and heterogeneity models using polychotomous scores (i.e., actual number of attempts), we can examine the polychotomous patterns. Table summarizes the frequencies of suicide attempts observed for each assessment interval. Although a sizeable number of subjects (8) made two or more attempts during the baseline interval, only (.) made two or more during the first 6-month follow-up period, and only - (.-.) made two or more during each of the subsequent follow-up intervals. Table suggests that the rate of suicide attempts over time closely parallels the trend reported for the rate of completed suicide over time: highest in the first 6 months following hospital admission, then rapidly diminishing to a low constant rate (Clayton, 98). Table describes the correlation (Spearman) between the actual number of suicide attempts for each pair of assessment intervals, calculated for the subset of patients who evidenced at least one attempt during any of the five intervals ( = 78). onattempters were excluded from this correlation matrix because their large numbers would have skewed the coefficients. Two observations from the table deserve mention. First, there was a consistent low-order negative correlation between the numbers of baseline and all follow-up interval attempts. Second, there was virtually no correlation between pairs of followup intervals. The significant positive correlation between the last two follow-up intervals was small and described a trend encompassing patients who made attempts during both intervals. The negative correlation observed between the numbers of baseline and all follow-up interval attempts may be explained in several ways. First, the baseline period was a variably sized one for each subject, encompassing "the current episode of disorder up to one year." Second, more than three times as many patients attempted suicide during the baseline interval ( = ) as attempted suicide during the highest frequency followup interval ( = 6 for -6 months). Third, in many cases recent suicide attempts or suicide risk was a precipitant for the index hospital admission; it is possible that those evidencing

5 6 CLARK, GIBBOS, FAWCETT, AD SCHEFTER Table Frequency of Suicide Attempts for Each Assessment Interval umber of attempts Baseline -6 months 7- months - 8 months 9- months I suicidal behavior or intentions on admission received disproportionate attention and treatment to reduce their suicide risk. This negative correlation observed between the numbers of baseline and follow-up interval attempts might be expected to confound the original state dependence/heterogeneity modeling analysis, because the model assumptions do not tolerate a mix of positively and negatively correlated events. Therefore, we reexamined the fit of the observed data to the three proposed models after excluding baseline period data, confining our attention to suicidal behavior coded dichotomously for the four follow-up intervals. The simple state dependence model was associated with a chi-square statistic of 86.7 on degrees of freedom (p =.), with p =.98. The simple heterogeneity model was associated with a chi-square statistic of 7. on degrees of freedom (p =.7). The combined model was associated with a chisquare statistic of 7. on 9 degrees of freedom (p =.), with p =. Thus the observed data showed an extremely poor fit to the state dependence model, and reasonable fits to the heterogeneity and combined models. Because the combined model provided no significant improvement of fit over the simple heterogeneity model, x ( =, ns, and because the combined model estimated the degree of true state dependence (rho) as nil, we conclude that the simple heterogeneity model alone is supported by the second analysis restricted to follow-up data. The average trend over time (jj.p) for this simple heterogeneity model was.. Because the ratio of the variable to its standard error (.7) was smaller than :, we cannot conclude that the trend was significantly different from zero. The nonsignificant group trend suggests that if baseline period suicidal behavior is ignored, there is no trend for patients as a group to evidence increasing or decreasing numbers of attempts over the -year follow-up. Predictive Value of Multiple Attempts It might be argued that by reducing the actual number of suicide attempts occurring during each assessment interval to a dichotomous score, we lose the ability to detect "flurries" of suicide attempts that may predict subsequent flurries or even death by suicide. The hypotheses underlying these objections to data reduction may be tested indirectly. Table summarizes the likelihood of observing multiple suicide attempts (defined as two or more attempts, and three or more attempts) during the subsequent follow-up interval for a variety of antecedent patterns. The data suggest that multiple attempters (defined by either threshold) are more likely to make subsequent multiple attempts. Association Between onlethal Attempts and Death by Suicide Although cases of completed suicide were excluded from the heterogeneity and state dependence models for the reasons previously cited, it is nonetheless instructive to examine the suicide attempt patterns for these cases. Table 6 summarizes the suicide Table Spearman Correlation of umber of Attempts Between Assessment Intervals for the Subset of Suicide Attempters Assessment intervals Baseline -6 months 7- months -8 months 9- months -6 months 7- months - 8 months 9- months -.97*** -.* -.*** -.7** _ *** ote. = 78. *p<..**p<.l.***p<.l.

6 MECHAISM UDERLYIG RECURRET SUICIDE ATTEMPTS 7 Table Relationship Between Antecedent Patterns and Subsequent Multiple Suicide Attempts Antecedent patterns Two or more attempts in following interval Three or more attempts in following interval Assessment intervals Frequency Baseline or more Baseline and -6 months All scores. All scores <. One score a Two scores a Baseline, -6 and 7- months All scores <. \ All scores <; One score ^ Two scores S: Baseline, -6,7-, and -8 months All scores <. \ All scores. One score a Two scores a attempt patterns coded polychotomously of subjects who died during the -year follow-up period (and were therefore excluded from all the previous analyses; see Subjects section). In Table 6, the final suicide attempt in each pattern for patients who died by suicide represents the lethal attempt. There is no indication that "flurries" of multiple nonlethal suicide attempts were associated with subsequent flurries or death by suicide. When the sample of 6 patients who completed suicide is compared with the original sample, the relation emerging between attempted and completed suicide can be seen in several different lights. Examining assessment periods one by one, the incidence of nonlethal attempts is similar for the suicide completers and the original sample. For example, /6 suicide completers () and /98 of the original sample () made nonlethal attempts during the baseline period (Fisher Exact Test [FET] =., two-tailed); and /6 suicide completers (9) and 6/98 of the original sample (7) made nonlethal attempts during the -6 month follow-up interval (FET =.9). The inability of nonlethal attempts to prospectively identify patients more likely to die by suicide in this sample has been discussed in more detail by Fawcett et al. (987). Summing over the baseline and follow-up periods, however, significantly more suicide completers (/6 or 6) made nonlethal attempts than subjects in the original sample (78/ 98 or ) (FET =.6). Only of subjects (9) who died of natural or accidental causes made any suicide attempts during the entire observation period; this rate is not significantly lower than that observed for the original sample (FET =. ). Discussion An application of a new statistical model to a longitudinal study of nonlethal suicide attempts among patients with affective disorder demonstrates that a simple heterogeneity model best describes these data. The findings suggest that the degree of association between past and future suicide attempts would disappear if individual patient differences on predisposition to suicide attempts could somehow be measured and controlled. One limitation of our analysis is the decision to quantify suicidal behavior during each assessment interval as a dichotomous (rather than a polychotomous) variable. The occurrence of several suicide attempts during one assessment interval was weighed the same as the occurrence of a single suicide attempt over that interval for purposes of predicting subsequent attempts. As a result, the predictive potential of several attempts over a short period of time (for example) may have been underestimated. The decision to score attempts dichotomously was dictated by the mathematical constraints of the models used rather than by clinical assumptions. A casual examination of the polychotomous data suggested that although flurries of attempts appeared to predict subsequent flurries, they were not associated with completed suicide. A second limitation is the arbitrary definition of follow-up intervals as 6-month periods. It is possible, for example, that we would obtain different results by working with shorter (e.g., -month) or longer (e.g., -year) intervals. There are two rationales for the choice of 6-month intervals: (a) The study design dictated that subjects were contacted for follow-up interviews at 6-month intervals, when they and significant others summarized events for the prior 6-month period; and (b) there is some evidence that the incidence of suicidal behavior is highest in the first 6 months following the index hospital admission, and then tapers off to a lower rate (Clayton, 98). A third limitation is our failure to examine potential sources

7 8 CLARK, GIBBOS, FAWCETT, AD SCHEFTER Table 6 Suicide Attempt Patterns (Polychotomous) for Subjects Who Died During the - Year Follow- Up Period Time lapsed Age at to death Pattern Sex intake (months:days) atural and accidental death (= ) Completed suicide ( = 6) : :7 : : 8: : : : 6: 8:7 : : :8 : : :7 :8 :6 : 7: 8: : : : :8 6: : of heterogeneity, such as age and center (i.e., geographic site). In our sample, for example, there was a low-order significant negative correlation between age and number of nonlethal attempts (r=-a9,p=.). In a subsequent report, we intend to systematically examine a variety of demographic, clinical, and personality correlates of the predisposition to nonlethal attempts we have denned. A fourth and important limitation was our assumption that each subject's propensity to attempt suicide over time was unaffected by all considerations other than subsequent suicide attempts. It is possible, of course, that a number of other clinical factors, such as type of treatment or changes in clinical status over time, could influence this propensity. An elaboration of Gibbons and Bock's (987) model that could account for these kinds of clinically relevant influences might yield a more veridical and useful model. Some of the results described may seem contradictory, but they can be reconciled. A history of one or more suicide attempts during the baseline period was significantly associated with a higher incidence of attempts during the total -year follow-up period. Yet we also observed a negative correlation between number of attempts during the baseline and all subsequent follow-up intervals for the subset of suicide attempters. These seeming inconsistencies may be explained by the fact that the vast majority of our sample ( = 6, or 7) never attempted suicide during the study period, and that the majority of patients who made any suicide attempts during the study period (9/78, or 7) only made one. When psychiatric patient samples are selected in a way that favors (directly or indirectly) those exhibiting suicidal behavior, the relation between attempts over time that emerges may be misleading. "Synchronizing" the illness course of all subjects by defining sample selection around a suicidal act or hospital admission (admission is often a function of suicidal acts) results in a high incidence of attempts per unit time for the preadmission baseline period, and (to a lesser extent) the first 6 months of follow-up. The high density of attempts during the baseline period creates a situation where most patients admitted with a recent suicide attempt (/, or 7) never again make an attempt within the study period. In addition, disproportionate clinical attention may be devoted to patients hospitalized for suicide attempts. The latter two factors may explain why the number of baseline attempts showed a different relation with follow-up attempts (negative correlation) than was apparent between the various follow-up intervals (generally no correlation). Once a year has lapsed from initial assessment, the incidence of subsequent episodes of depression and suicidal behavior are "desynchronized" to yield a low and constant base rate of attempts. The practical implication of these findings is to suggest that when considering patients with moderate to severe major affective disorder, the clinician should not interpret the absence of any recent suicide attempt to mean that the patient is at relatively low risk for attempting or dying by suicide in the future. An implication of the heterogeneity model is that suicide attempts made many years ago have equal value to recent attempts when estimating an individual's predisposition to nonlethal attempts in the future. Although number of lifetime suicide attempts might constitute a reasonable estimate of a patient's predisposition to nonlethal attempts (as defined by the heterogeneity model), there are at least two circumstances that confound this assumption. First, an individual who has not yet traversed most of his or her life risk for suicidal behavior (i.e., younger individuals) may not have had the opportunity to express that potential. Second, life circumstances may facilitate or inhibit the expression of predisposition to nonlethal attempts, so that an individual's very high potential could go unexpressed for a considerable period of time until life conditions were ripe for its expression. These findings also direct the attention of clinical investigators to the attributes of the individual that may bear on predisposition to nonlethal attempts. Our findings do not clarify whether this predisposition is a function of psychopathology, life history, personality, early development, neurophysiology, or genetics; nor does it clarify the chronological age of onset for the predisposition, or the long-term predictive value of the predisposition. Impressively little consensus has developed in the field of suicidology on person-specific qualities associated with greater likelihood of suicidal behavior, though some investigators have decried this lack and issued calls for renewed research efforts in this area. Smith (98), for example, hypothesized that four premorbid personality characteristics (high self-expectations, tendency to suppress dysphoric affect, sober but ambivalent feelings about death, and inability to mourn the loss of unrealistic gratifications) predispose the individual to a higher

8 MECHAISM UDERLYIG RECURRET SUICIDE ATTEMPTS 9 risk of death in a suicidal crisis. Motto (986) has reviewed and critically evaluated current biological evidence bearing on the correlates of suicidal behavior. The limited informational value of suicide attempts for prediction purposes appears to apply to data on suicide completion as well. Only a third of suicide completers evidence a history of previous suicide attempts (Robins, Gassner, Kayes, Wilkinson, &Murphy, 99;Dorpat&Ripley, 96; Rood &Seager, 968; Barraclough, Bunch, elson, & Sainsbury, 97; Roy, 98; Rich, Young, & Fowler, 986; Fawcett, Scheftner, Hedeker, Gibbons, & Coryell, 987), and prospective studies have failed to demonstrate a significant relation between previous suicide attempts and death by suicide in large unselected samples (Clayton, 98). Fawcett et al. (987), for example, reporting on adult deaths by suicide in the same sample of 9 patients with affective disorder, noted that (a) of those who died by suicide had no prior history of suicidal attempts; and (b) severity of suicidal ideation, medical lethality of suicide attempts, and number of prior suicide attempts at initial assessment showed no significant association with ultimate death by suicide. References Andreasen,., Grove, W., Shapiro, R., Keller, M. B., Hirschfeld, R. M. A., & McDonald-Scott, P. (98). Reliability of lifetime diagnoses: A multi-center collaborative perspective. Archives of General Psychiatry, 8, -. Aneshensel, C. S., Estrada, A. L., Hansell, M. J., & Clark, V. A. (987). Social psychological aspects of reporting behavior: Lifetime depressive episode reports. Journal of Health and Social Behavior, 8, - 6. Barraclough, B., Bunch, J., elson, B., & Sainsbury, P. (97). A hundred cases of suicide: Clinical aspects. British Journal of Psychiatry,, -7. Buglass, C. D., & Morton, J. (97). The repetition of parasuicide: A comparison of three cohorts. British Journal of Psychiatry,, Clayton, P. J. (98). Suicide. Psychiatric Clinics of orth America, 8, -. Dorpat, T. L., & Ripley, H. S. (96). A study of suicide in the Seattle area. Comprehensive Psychiatry,, 9-9. Endicott, J., & Spitzer, R. (978). A diagnostic interview: The Schedule for Affective Disorders and Schizophrenia. Archives of General Psychiatry,, Fawcett, J., Scheftner, W. A., Clark, D. C., Hedeker, D., Gibbons, R. D., & Coryell W. (987). Clinical predictors of suicide in patients with major affective disorders: A controlled prospective study. American Journal of Psychiatry,, -. Flood, R., & Seager, C. (968). A retrospective examination of psychiatric case records of patients who subsequently committed suicide. British Journal of Psychiatry,, -. Gibbons, R. D., & Bock, R. D. (987). Trend in correlated proportions. Psychometrika,, -. Heckman, J. J. (98). Statistical models for discrete panel data. In E. F. Manski & D. M. McFadden (Eds.), Structural analysis of discrete data: With econometric applications (pp. -7). Cambridge: MIT Press. Heckman, J. J., & Borjas, G. J. (979). Does unemployment cause future unemployment? Definitions, Questions and answersfrom a continuous time model of heterogeneity and state dependence (Rep. o. 79). Chicago: Center for Mathematical Studies in Business and Economics, University of Chicago. Katz, M., & Klerman, G. (979). Overview of the clinical studies program. American Journal of Psychiatry, 6, 9-. Keller, M., Lavori, P., Andreasen,., Grove, W. M., Shapiro, R. W., Scheftner, W. A., & McDonald-Scott (98la). Test-retest reliability of assessing psychiatrically ill patients in a multi-center design. Journal of Psychiatric Research, 6, -7. Keller, M., Lavori, P., McDonald-Scott, P., Scheftner, W. A., Andreasen,. C., Shapiro, R. W., & Croughan, J. (98 Ib). Reliability of lifetime diagnoses and symptoms in patients with a current affective disorder. Journal of Psychiatric Research, 6, 9-. Keller, M., Lavori, P., Friedman, B., ielsen, E., McDonald-Scott, B., Andreasen,. C., & Endicott, J. (987). The LIFE: A comprehensive method for assessing outcome in prospective longitudinal studies. Archives of General Psychiatry,, -8. Morgan, H. G., Barton, J., Pottle S., Pocock, H., & Burns-Cox, C. J. (976). Deliberate self-harm: A follow-up study of 79 patients. British Journal of Psychiatry, 8, Motto, J. A. (986). Clinical considerations of biological correlates of suicide. Suicide and Life-Threatening Behavior, 6, 8-. Rich, C. L., Young, D., & Fowler, R. C. (986). San Diego Suicide Study: I. \bungvs. old subjects. Archives of General Psychiatry,, Robins, E., Gassner, S., Kayes, J., Wilkinson, R. H., & Murphy, G. (99). The communication of suicidal intent: A study of consecutive cases of successful (completed) suicide. American Journal of Psychiatry,, 7-7. Roy, A. (98). Risk factors for suicide in psychiatric patients. Archives of General Psychiatry, 9, Schmidt, E. H., O'eal, P., & Robins, E. (9). Evaluation of suicide attempts as guide to therapy. Journal of the American Medical Association,, 9-7. Siani, R., Garzotto,., Zimmerman-Tansella, C., & Tansella, M. (979). Predictive scales for parasuicide repetition: Further results. Acta Psychiatrica Scandinavica, 9, 7-. Smith, K. (98). Suicide assessment: An ego vulnerabilities approach. Bulletin ofthemenninger Clinic, 9, Spitzer, R., Endicott, J., & Robins, E. (978). Research Diagnostic Criteria: Rationale and reliability. Archives of General Psychiatry,, Stengel, E. (96). Suicide. Bristol, England: MacGibbon and Kee. Received February,988 Revision received August, 988 Accepted October 9,988