Journal of Affectbe Disorders, 22 ( 1991) 11 1- 118 c 1991 Elsevier Science Publishers B.V. 0165.0327/91/$03.50 ADONIS 016503279100098C
111
JAD 00811
Can future suicidal behaviour in depressed patients be predicted? Conor F. Duggan,
Pak Sham, Alan S. Lee ’ and Robin M. Murray
Genetics Section, Department of Psychological Medicine, Institute of Psychiatry and Kings College Hospital, London and ’ Department of Psychiatry, Unkersity Hospital, Nottingham, U.K. (Received 30 November 1990) (Revision received 8 March 1991) (Accepted 18 March 1991)
Summary The determinants of suicidal behaviour over 18 years were examined in a series of 89 depressed in-patients, using index data on clinical features, personality, and history of past loss. Seven variables were selected from univariate analyses and their relationship with (1) the presence or absence, (2) frequency, (3) intent, and (4) medical threat of suicidal behaviour was then explored by generalised linear modelling. Severe dysphoria, past alcoholism and chronic physical illness were most predictive of suicidal attempting; however, different variables predicted the frequency, degree of intent and severity of medical threat of subsequent suicidal attempts. Thus, our results suggest that different aspects of long-term suicidal behaviour have different determinants.
Key words: Suicidal
behaviour;
Depression;
Risk factors
Introduction Despite the well-recognised association between mental illness and suicide (Barraclough et al., 1974; Miles, 1977), the practising psychiatrist finds it difficult to predict future suicidal risk (Pokorny, 1983; Allgulander and Fisher, 1990). Suicidal behaviour is particularly common among depressed patients (Guze and Robins, 1970); here,
Address for correspondence: Conor F. Duggan BSc, PhD, MRCPsych, Genetics Section, Department of Psychological Medicine, Institute of Psychiatry and Kings College Hospital, Denmark Hill, London SE5 9RS, U.K.
phenomenology appears more important than nosology (Beskow, 1990); with severity (Barraclough et al., 1974), a sense of hopelessness (Beck et al., 1985), neurovegetative signs (Bulik et al., 1990), and past attempts (Barraclough and Pallis, 1975) all being linked to subsequent suicidal behaviour. The concept of a ‘suicidal personality’ is no longer fashionable (Philip, 1970), but personality features such as hostility (Paykel and Dienelt, 1971; Farmer and Creed, 1989), dependence (Berglund et al., 1987) and obsessionality (Murthy, 1969) have all been found to be associated with suicidal behaviour, as has an experience of early loss (Greer, 1961; Birtchnell, 1970; Adam et al., 1982).
112
The usefulness of these findings is diminished, however, by their inconsistency across studies. Sources of variability arise from the heterogeneity in the samples studied, the lack of clear definitions of the putative predictor variables (Adam et al., 19821, and the use of inappropriate statistics (Leon et al., 1990). For example, the failure to examine several variables simultaneously has meant that variables whose apparent effect is explained by some other variable have not been eliminated. Another difficulty in cross-sectional studies which attempt to find predictors after the suicide attempt has been made, is that such retrospective data are prone to bias. Finally, most studies have considered suicidal behaviour as a dichotomous variable, without taking account of the frequency of attempts, degree of intent, or the severity of medical threat. It is not clear, however, whether variables which predict suicidal behaviour dichotomously also predict these other aspects of such behaviour. This report, which relates suicidal behaviour longitudinally over an 18-year period to a number of variables measured at the index admission, overcomes many of these difficulties. Our objective was to identify predictors of various aspects of suicidal behaviour and determine their consistency. Methods This series has been described in detail elsewhere (Lee and Murray, 1988). Briefly, the sample was drawn from a consecutive series of 89 in-patients (Kendell, 19681, whose long-term outcome was assessed 18 years after the index admission (see Fig. I). The original sample consisted of 62 females and 27 males; the mean age at index was 38.8 (SD = 12.5) years with range of 16-67 years. All subjects met the RDC criteria for major depressive disorder (Spitzer et al., 1978), and were categorised into various depressive subtypes using information from the case notes, by R.M.M. who was blind to their subsequent course. Their personality was assessed using the Eysenck Personality Inventory (EPI; Eysenck and Eysenck, 1964) and the Leyton Obsessional Inventory (LOI; Cooper, 1970). These were administered both when the patients were ill and when they were
believed to have recovered (Kendell and Discipio, 1968, 1970). In a replication of their earlier findings on past loss and symptom formation in depression, Brown et al. (1977) rated past loss in all the female members of the series from the case notes. This was defined as a loss of a parent before the age of 17 either by (a) death or (b) separation of parents or (c> long-term (i.e., 1 year or more) separation from the parent during the patient’s childhood (e.g., from hospital care, war evacuation, etc.); the loss of a spouse or sibling because of death; or the loss of a child through either death or adoption. Subsequently, R.M.M. rated all the males in the series according to the same criteria. Eighty-eight of the individuals in the series (98%) were located after 18 years, and 56 of the survivors (86%) were interviewed by A.S.L. who was blind to all the proband data including those concerning personality and past loss (Lee and Murray, 1988). The data on attempted suicide were derived from the SADS-L (Endicott and Spitzer, 1979) interview at follow-up wherein the individual was questioned about (a) the presence and number of suicide attempts, (b) his or her intent at the time of the most serious attempt, (c> the actual medical threat to life following the most serious attempt. Individuals who had committed suicide were categorised as having an extreme degree of medical threat. Wherever possible, the interview data from the SADS-L were corroborated by information from hospital case notes and the patient’s general practitioner. In every case where the patient had died during the follow-up period, the death certificate was obtained and the cause of death ascertained (Lee and Murray, 1988). In examining the risk factors for suicidal behaviour, we grouped together those who had attempted or completed suicide; henceforth referred to as suicide ‘attempters’ (see Fig. 1). We hypothesised that the severity of depression, the presence of previous suicidal attempts, and certain other characteristics of the depression increase the risk of future suicidal behaviour. In addition, we hypothesised that a history of loss and personality abnormalities would also have a positive association with suicidal behaviour. These
113
Original
sample
Traced
(n = 89)
18 years later?
Yes (n = X8> I Alive?
No (n = 1)
I
I Yes (n = 65) I Interviewed by SADS-L?
r-----l
Yes (n = 56)
No (n = 9)
No (n = 23) I Suicide?
’
Yes (n = 5)
No (n = 181
I Attempted
suicide?
Yes (n = 24)
No (n = 32) Fig. 1. Composition
predictions were examined using Fisher’s exact test for the discrete variables and Student’s t-test for the continuous measures. Variables with a significant or near-significant effect in the univariate analysis were then entered into generalised linear models (McCullagh and Nelder, 1989) as predictor variables for the presence/ absence of suicidal behaviour; and the frequency, intent and medical threat of such behaviour. The prediction of the presence/absence, and the frequency of suicidal behaviour was performed with the program GLIM. For the former the logistic model was used, assuming that the outcome variable has a binomial distribution and is ‘linked’ to the predictors by a logit function. For the latter we used the log-linear model, assuming a Poisson distribution for the number of attempts and a log link function. The prediction of the intent and medical threat of attempts was performed by the LOGIST procedure of SAS, under the option for ordinal logistic regression. In each analysis a backward stepwise procedure was used so that variables whose deletion did not significantly decrease the fit of the model were removed.
OF sample.
Results The composition of the sample is shown in Fig. 1. Suicidal attempting was common with 24 of the 56 interviewed survivors (43%) making at least one attempt in the follow-up period (Table 1). To these 24 attempters were added the five individuals (6% of the total sample) who committed suicide. Thus, 29 attempters and 32 non-attempters formed the two comparison groups in the univariate analyses. The two groups did not differ significantly with regard to gender or social class. Similarly, there was no difference in the mean age of onset or the presence or absence of previous depression. Both severe dysphoria at the index admission and psychomotor retardation were positively associated with subsequent suicidal behaviour (P = 0.02 and 0.045 respectively, see Table 2). Historical information implicated previous brain injury as significant (P = 0.02). A history of alcoholism, past suicidal attempting and chronic physical illness were also associated with suicidal behaviour, although none of these reached statistical significance (P = 0.1). Classification into various de-
114
pressive subtypes was non-discriminatory as none of these, whether clinically or operationally defined according to RDC or DSM-III, showed any effect. The experience of loss was more common among suicide attempters (59%) as compared to the non-attempters (37.5%) (Table 2). When this loss was further subdivided into loss by death and by separation, the difference between suicide attempters and non-attempters was accounted for entirely by loss through separation; the former had more than twice the amount of loss than the latter. Loss by separation was associated with suicidal attempting (P = 0.045) whereas loss by death was not (P = 0.58). Against expectations, none of the results from the personality tests (EPI and LOI) administered when the patient had recovered showed any association with subsequent suicidal attempting nor did personality disorder diagnosed according to DSM-III (Table 2). As the combination of completers and attempters is questionable, the same analyses were performed excluding the five individuals who comTABLE
1
CHARACTERISTICS YEARS FOLLOW-UP
OF SUICIDAL
BEHAVIOUR
Frequency Number 0 1 2 3 4 5 6 7 8
ofattempts 32 8 4 4 3 0 1 2 2
Intent Not rated Minimal Serious Very serious Extreme Medical threat Not rated Mild Moderate Severe Extreme (death
3 9 I 4 1
by suicide)
2 6 10 6 5
IN 18
TABLE
2
PREDICTORS
OF SUICIDE
ATTEMPTS
Suicide -
Suicide +
DepresCe symptom Severe no dysphoria yes Retarded no yes Agitated no yes
32 0 27 5 26 6
24 5 18 11 20 9
Depressice subtypes Psychotic no yes DSM-III no melancholic yes RDC no bipolar yes no RDC secondary yes
20 12 18 14 21 4 27 4
14 15 13 16 25 4 24 5
Past history Previous suicidal attempts Family history of psychosis Family history of neurosis Previous brain damage Chronic physical illness History of alcoholism Loss by death Loss by separation
no yes no yes no yes no yes no yes no yes no yes no yes
20 12 27 5 31 1 32 0 32 0 32 0 25 7 27 5
13 16 22 7 26 3 24 5 26 3 26 3 23 6 18 11
no yes
21 11
21 8
Personality DSM-III personality disorder
Inoentory (on recovery of index illness) a EPI neuroticism 14.4 extraversion 12.1 20.7 LO1 symptoms traits 9.8 resistance 13.4 interference 12.8
(0.8) (1.0) (2.1) (1.0) (1.8) (2.6)
-
14.8 12.7 20.4 8.7 15.2 16.3
P (one tailed)
0.02 0.045 0.2
0.2 0.3 0.6 0.5
0.1 0.4 0.3 0.02 0.1 0.1 0.58 0.045
0.4
(0.3) (0.8) (1.7) (0.8) (2.0) (2.5)
0.8 0.6 0.9 0.4 0.5 0.3
’ Mean scores k SE.
pleted suicide. The results were broadly similar, as one might expect from the small number of suicide completers. The biggest change was that
115
the P-value for a history of alcoholism increased from 0.1 to 0.43, when those who had committed suicide were excluded. TABLE
3
GENERALISED HAVIOUR
LINEAR
MODELS
FOR
SUICIDAL
Backward logistic regression: presence/absence of suicidal attempts Variables removed Scaled deviance None 47.049 + Retardation 47.643 + Separation 50.373 + Brain damage 53.281 + Previous suicide attempts 55.621 Variables selected Coefficient 9.85 Severe dysphoria Chronic physical illness 9.31 Previous alcoholism 9.31
df 45 46 47 48 49 SE 27.36 33.02 33.02
Backward loglinear modelling: frequency of suicidal attempts Variables removed None + Retardation + Previous alcoholism + Brain damage + Chronic physical illness Variables selected Severe dysphoria Separation Previous suicide attempts
df 40 41 42 43 44 SE 0.26 0.25 0.30
Scaled deviance 82.116 82.314 83.693 85.813 88.290 Coefficient 1.35 0.56 1.24
Backward ordinal logistic regression: intent of suicidal attempts Variables removed Scaled deviance 77.61 None 77.64 + Retardation 80.30 + Chronic physical illness + Previous suicidal attempts 82.85 Coefficient Variables selected - 9.46 Previous alcoholism Separation 1.53 Severe dysphoria 3.31 Brain damage 1.59 Backward ordinal logistic regression: medical threat of suicidal attempts Variables removed Scaled deviance 113.85 None 114.57 + Separation 115.29 + Severe dysphoria + Brain damage 117.21 + Previous alcoholism 119.72 Variables selected Coefficient Previous suicidal attempts 1.74 1.69 Retardation Chronic physical illness 2.85
BE-
df 40 41 42 43 SE
_ 0.69 1.12 0.74
df 45 46 47 48 49 SE 0.62 0.62 1.27
The following seven variables - chronic physical illness, psychomotor retardation, severity of mood disturbance, past attempting, history of alcoholism, of separation and of brain damage were selected for further exploration with generalised linear models (Table 3). The presence or absence of suicidal behaviour was significantly predicted by severe dysphoria, past alcoholism and chronic physical illness. The large standard errors of the parameter estimates are due to the fact that few individuals have these characteristics, but those who do are all attempters. For this reason, the odds ratios for these effects cannot be estimated accurately, even though we have evidence that they are greater than 1. In contrast to the presence or absence of suicidal behaviour, the frequency of attempting was significantly related to severe dysphoria, past suicidal attempts, and separation. Similarly, the predictors of the degree of intent and medical threat were different: intent was predicted by severe dysphoria, brain damage, past alcoholism and separation; and threat by chronic physical illness, past suicidal attempts and psychomotor retardation. The interpretation of the coefficients is made easier by taking their exponents, e.g., having severe dysphoria increases the number of attempts on average by a factor of e’.35 or 3.86. The model for predicting the presence/ absence of suicidal behaviour fitted the data fairly well (scaled deviance = 55.6, df = 49, P > 0.2), but the fit of the other models was poor. Discussion Despite an extensive literature on suicide, few long-term prospective studies have attempted to identify risk factors (Beck and Steer, 1989). Although our index data were not collected specifically to address the question of future suicidal behaviour, the problem of retrospective bias is overcome by concentrating solely on these data. However, the information on the suicidal attempt is retrospective and hence is subject to recall error. For instance, the measurement of suicidal intent is especially difficult, and therefore one should be cautious in interpreting the results. Certain other limitations also need to be acknowledged. Firstly, we grouped together suicide
116
attempters and completers. As these may represent two different populations Kreitman, 1977), some may question their combination. However, we have shown that the exclusion of suicide completers did not change the results significantly, except for alcoholism, although this is not surprising in view of the small number of suicide completers in the sample. Secondly, in making 23 comparisons, there is a danger of finding spurious relationships. While this is a valid consideration, an examination of our data (Table 2) shows that the 23 comparisons produced four with a P-value of < 0.05 and three further comparisons of P < 0.1, figures which are greater than the one or two results of significance which may be expected to arise by chance. Nevertheless, caution should be exercised in interpreting these results as some may be falsely positive. Thirdly, the numbers in some of the cells are small, so that statistical power is limited. This is a particular problem for the analysis of the subtyping data where our failure to find an effect may have been due to small sample sizes. These limitations aside, our results indicate that among patients hospitalised with depression, subsequent suicidal behaviour was extremely common, with almost half the sample (48%) either attempting or completing suicide over the 18 years follow-up. Moreover, this is not an isolated result as a similar study by Andrews et al. (1990) has produced almost identical figures for completed suicide, 11 of 193 patients (5.7%) followed up for 15 years committing suicide. What features, therefore, led patients to engage in subsequent suicidal behaviour? There were few surprises among the variables showing a positive association with suicidal behaviour in the univariate analyses. As many previous investigations have relied on cross-sectional data, however, similar findings from our longitudinal design offer important confirmation. Previous work already identifying severity of depression (Bulik et al., 1990), psychomotor retardation (Barraclough and Pallis, 1975) and alcoholism (Beck and Steer, 1989) as having important associations with suicidal behaviour is supported by our data. Further subtyping the index depressive episode failed to show any relationship with such behaviour, a negative finding again supported by
a recent prospective investigation (Fawcett et al., 1987). Our finding that loss by separation but not loss by death was associated with subsequent suicidal behaviour also replicates previous findings (Crook and Raskin, 1975; Bronisch and Hecht, 1987). An explanation for this differential effect may be that it is family instability and discord prior to the loss that is important in leading to subsequent suicide behaviour (Adam et al., 1982) and that such instability is more common in loss by separation. The negative results from the personality inventories and from the DSM-III classification of personality were surprising. This may be a reflection of the inventories used which may not identify the personality types (often aggressive, impulsive or borderline) associated with suicidal behaviour (Angst and Clayton, 1986). Another possible reason for our failure to find any effect of personality is that we have examined a depressed sample, as Bronisch and Hecht (1987) also failed to establish a relationship between abnormal personality and suicidal behaviour in depressed patients, while Casey (1987) found an apparent relationship which disappeared after controlling for the severity of depression. What of our more ambitious aim of eliminating redundant influences by generalised linear modelling? With the dichotomy of the presence or absence of suicide attempt, it was possible to reduce the number of variables with a significant effect to three: severe dysphoria, alcoholism and chronic physical illness. However, this dichotomisation is simplistic as suicidal activity itself is not an all-or-none phenomenon; rather it represents a diverse spectrum of behaviours. That this is so has previously been demonstrated by the differential association of certain predictors with the different aspects of suicidal behaviour (Plutchik et al., 1989). In our study, severe dysphoria and separation were most strongly associated with frequency of attempting, but they had the least effect as regards medical threat (i.e., the more severe and sometimes fatal suicidal activity). Conversely, psychomotor retardation had an effect for medical threat but very little for frequency of attempting. Thus, there is a suggestion that the features which lead individuals to make many attempts do not predict completed suicide and
117
vice versa (Kreitman, 1977). These differences in the predictors are also reflected in our finding only a moderate correlation (Spearman’s p = 0.59, P < 0.003) between frequency and medical threat in the surviving attempters. These speculations need to be tempered by recognising the limitations of the study. As one might expect, the model with the best fit was the presence/absence of suicidal behaviour as this was the simplest to predict. The models for frequency, intent and threat were more complex and consequently had a relatively poorer fit. This lack of predictive power may partly be due to the sole reliance on index variables, since in a follow-up of 18 years such influences can best be regarded as predisposing factors. Their influence might therefore have been considerably strengthened if we had been able to take additional later developments into account. In some respects, depression itself may be regarded as a predisposing factor leading to suicidal behaviour through the development of additional complications. Psychiatric complications were common in this series (Lee and Murray, 1988). For example, the number of individuals with alcoholism increased from 3% at index to 10% some 18 years later. These additional cases increased the statistical significance of the relationship between alcoholism and ever attempting suicide from P = 0.1 to P = 0.06. Thus depression itself may lead to suicide but in addition, it provides fertile ground for the develapment of other social and psychiatric complications which bring in their train further risks of suicidal behaviour. Acknowledgements The authors would like to acknowledge the contributions of Professors R.E. Kendell and G. Brown and colleagues whose initial assessment of the sample made this report possible. Financial support was provided by the Mental Health Foundation, the Bethlem and Maudsley Fund, the Wellcome Trust and the Medical Research Council. References Adam, K.S., Bouckoms, A. and Streiner, loss and family stability in attempted Psychiatry 39, 1081~1085.
D. (1982) Parental suicide. Arch. Gen.
Allgulander, C. and Fisher. L.D. (1990) Clinical predictors of completed suicide and repeated self-poisoning in 8895 self-poisoning patients. Eur. Arch. Psychiatry Neurol. Sci. 239, 270-276. Andrews, G.. Neilson, M., Hunt, C., Stewart, G. and Kiloh, L.G. (1990) Diagnosis, personality and long-term outcome of depression. Br. J. Psychiatry 157, 13-18. Angst, J. and Clayton, P. (198hJ Premorbid personality of depressive. bipolar, and schizophrenic patients with special reference to suicidal issues. Compr. Psychiatry 27, 51 l-532. Barraclough, B.M. and Pallis, D.J. (1975) Depression followed by suicide: a comparison of depressed suicides with living depressives. Psychol. Med. 5. 55-61. Barraclough, B.M., Bunch, J., Nelson, B. and Sainsbuty. P. (1974) A hundred cases of suicide: clinical aspects. Br. J. Psychiatry 125. 355-373. Beck, A.T. and Steer. R.A. (1989) Clinical predictors of eventual suicide: a 5 to 10 year prospective study of suicide attempters. J. Affect. Disord. 17, 203-209. Beck, A.T., Steer, R.A.. Kovacs, M. and Garrison, B. (1985) Hopelessness and eventual suicide: a IO-year prospective study of patients hospitalised with suicidal ideation. Am. J. Psychiatry 142, 559-563. Berglund, M., Krantz, P.. Lundqvist. G. and Therup, L. (1087) Suicide in psychiatric patients. Acta Psychiatr. Stand. 76, 43 l-437. Beskow, J. (1990) Depression and suicide. Pharmacopsychiatry 23, 3-8. Birtchnell. J. (1970) The relationship between attempted suicide, depression and parent death. Br. J. Psychiatry 116, 303-313. Bronisch. T. and Hecht, H. (1987) Comparison of depressed patients with and without suicide attempts in their past history. Acta Psychiatr. Stand. 76, 438-449. Brown, G.W., Harris, T. and Copeland, J.R. (1977) Depression and loss. Br. J. Psychiatry 130, l-18. Bulik, CM., Carpenter, L.L., Kupfer, D.J. and Frank, E. (1990) Features associated with suicide attempts in recurrent major depression. J. Affect, Disord. 18, 29-37. Casey, P. (19x9) Personality disorder and suicide intent, Acta Psychiatr. Stand. 7Y, 290-295. Cooper, J. (1970) The Leyton Obsessional Inventory. Psychol. Med. 1, 48-64. Crook, T. and Raskin, A. (1975) Association of childhood parental loss with attempted suicide and depression. J. Consult. Clin. Psychol. 43, 277. Endicott, J. and Spitzer, R.L. (1979) Use of the Research Diagnostic Criteria and the ‘Schedule of Affective Disorders and Schizophrenia’ to study affective disorders. Am. J. Psychiatry 136, 52256. Eysenck, H.J. and Eysenck, S.B.G. (1964) Manual of the Eysenck Personality Inventory. University of London Press. London. Farmer, R. and Creed. F. (1989) Life events and hostility in self-poisoning. Br. J. Psychiatry 154, 390-395. Fawcett, J., Scheftner, W., Clark, D., Hedeker, D., Gibbons, R. and Coryell, W. (1987) Clinical predictors of suicide in patients with major affective disorders: a controlled prospective study. Am. J. Psychiatry 144. 35-40.
118 Greer, S. (1961) The relationship between parental loss and attempted suicide: a control study. Br. J. Psychiatry 110, 698-705. Guze, S.B. and Robins, E. (1970) Suicide and primary affective disorders. Br. J. Psychiatry 117, 437-438. Kendell, R.E. (1968) The Classification of Depressive Illnesses (Institute of Psychiatry, Maudsley Monographs No. 18). Oxford University Press, London. Kendell, R.E. and Discipio, W.J. (1968) Eysenck Personality Inventory scores of patients with depressive illness. Br. J. Psychiatry 114, 767-770. Kendell, R.E. and Discipio, W.J. (1970) Obsessional symptoms and obsessional personality traits in patients with depressive illness. Psychol. Med. 1, 65-72. Kreitman, N. (1977) Parasuicide. Wiley, Chichester. Lee, AS. and Murray, R.M. (1988) The long-term outcome of Maudsley depressives. Br. J. Psychiatry 153, 741-751. Leon, A.C., Friedman, R.A., Sweeney, J.A., Brown, R.P and Mann, J.J. (1990) Statistical issues in the identification of risk factors for suicidal behaviour: the application of survival analysis. Psychiatry Res. 31, 99-108.
McCullagh, P. and Nelder, J.A. (1989) Generalised Linear Models. Chapman and Hall, London. Miles, C.P. (1977) Conditions predisposing to suicide: a review. J. Nerv. Ment. Dis. 164, 231-245. Murthy, V.N. (1969) Personality and the nature of suicide attempts. Br. J. Psychiatry 115, 791-795. Paykel, E.S. and Dienelt, M.N. (1971) Suicide attempts following acute depression. J. Nerv. Ment. Dis. 153. 234-243. Philip, AS. (1970) Traits, attitudes and symptoms in a group of attempted suicides. Br. J. Psychiatry 116, 475-482. Plutchik, R., Van Praag, H.M., Picard, S., Conte, H.R. and Korn, M. (1989) Is there a relation between the seriousness of suicidal intent and the lethality of the suicidal attempt? Psychiatry Res. 27, 71-79. Pokorny, A.D. (1983) Prediction of suicide in psychiatric patients. Arch. Gen. Psychiatry 40, 249-257. Spitzer, R.L., Endicott, J. and Robins, E. (1978) Research Diagnostic Criteria: rationale and reliability. Arch. Gen. Psychiatry 35, 773-782.
111
JAD 00811
Can future suicidal behaviour in depressed patients be predicted? Conor F. Duggan,
Pak Sham, Alan S. Lee ’ and Robin M. Murray
Genetics Section, Department of Psychological Medicine, Institute of Psychiatry and Kings College Hospital, London and ’ Department of Psychiatry, Unkersity Hospital, Nottingham, U.K. (Received 30 November 1990) (Revision received 8 March 1991) (Accepted 18 March 1991)
Summary The determinants of suicidal behaviour over 18 years were examined in a series of 89 depressed in-patients, using index data on clinical features, personality, and history of past loss. Seven variables were selected from univariate analyses and their relationship with (1) the presence or absence, (2) frequency, (3) intent, and (4) medical threat of suicidal behaviour was then explored by generalised linear modelling. Severe dysphoria, past alcoholism and chronic physical illness were most predictive of suicidal attempting; however, different variables predicted the frequency, degree of intent and severity of medical threat of subsequent suicidal attempts. Thus, our results suggest that different aspects of long-term suicidal behaviour have different determinants.
Key words: Suicidal
behaviour;
Depression;
Risk factors
Introduction Despite the well-recognised association between mental illness and suicide (Barraclough et al., 1974; Miles, 1977), the practising psychiatrist finds it difficult to predict future suicidal risk (Pokorny, 1983; Allgulander and Fisher, 1990). Suicidal behaviour is particularly common among depressed patients (Guze and Robins, 1970); here,
Address for correspondence: Conor F. Duggan BSc, PhD, MRCPsych, Genetics Section, Department of Psychological Medicine, Institute of Psychiatry and Kings College Hospital, Denmark Hill, London SE5 9RS, U.K.
phenomenology appears more important than nosology (Beskow, 1990); with severity (Barraclough et al., 1974), a sense of hopelessness (Beck et al., 1985), neurovegetative signs (Bulik et al., 1990), and past attempts (Barraclough and Pallis, 1975) all being linked to subsequent suicidal behaviour. The concept of a ‘suicidal personality’ is no longer fashionable (Philip, 1970), but personality features such as hostility (Paykel and Dienelt, 1971; Farmer and Creed, 1989), dependence (Berglund et al., 1987) and obsessionality (Murthy, 1969) have all been found to be associated with suicidal behaviour, as has an experience of early loss (Greer, 1961; Birtchnell, 1970; Adam et al., 1982).
112
The usefulness of these findings is diminished, however, by their inconsistency across studies. Sources of variability arise from the heterogeneity in the samples studied, the lack of clear definitions of the putative predictor variables (Adam et al., 19821, and the use of inappropriate statistics (Leon et al., 1990). For example, the failure to examine several variables simultaneously has meant that variables whose apparent effect is explained by some other variable have not been eliminated. Another difficulty in cross-sectional studies which attempt to find predictors after the suicide attempt has been made, is that such retrospective data are prone to bias. Finally, most studies have considered suicidal behaviour as a dichotomous variable, without taking account of the frequency of attempts, degree of intent, or the severity of medical threat. It is not clear, however, whether variables which predict suicidal behaviour dichotomously also predict these other aspects of such behaviour. This report, which relates suicidal behaviour longitudinally over an 18-year period to a number of variables measured at the index admission, overcomes many of these difficulties. Our objective was to identify predictors of various aspects of suicidal behaviour and determine their consistency. Methods This series has been described in detail elsewhere (Lee and Murray, 1988). Briefly, the sample was drawn from a consecutive series of 89 in-patients (Kendell, 19681, whose long-term outcome was assessed 18 years after the index admission (see Fig. I). The original sample consisted of 62 females and 27 males; the mean age at index was 38.8 (SD = 12.5) years with range of 16-67 years. All subjects met the RDC criteria for major depressive disorder (Spitzer et al., 1978), and were categorised into various depressive subtypes using information from the case notes, by R.M.M. who was blind to their subsequent course. Their personality was assessed using the Eysenck Personality Inventory (EPI; Eysenck and Eysenck, 1964) and the Leyton Obsessional Inventory (LOI; Cooper, 1970). These were administered both when the patients were ill and when they were
believed to have recovered (Kendell and Discipio, 1968, 1970). In a replication of their earlier findings on past loss and symptom formation in depression, Brown et al. (1977) rated past loss in all the female members of the series from the case notes. This was defined as a loss of a parent before the age of 17 either by (a) death or (b) separation of parents or (c> long-term (i.e., 1 year or more) separation from the parent during the patient’s childhood (e.g., from hospital care, war evacuation, etc.); the loss of a spouse or sibling because of death; or the loss of a child through either death or adoption. Subsequently, R.M.M. rated all the males in the series according to the same criteria. Eighty-eight of the individuals in the series (98%) were located after 18 years, and 56 of the survivors (86%) were interviewed by A.S.L. who was blind to all the proband data including those concerning personality and past loss (Lee and Murray, 1988). The data on attempted suicide were derived from the SADS-L (Endicott and Spitzer, 1979) interview at follow-up wherein the individual was questioned about (a) the presence and number of suicide attempts, (b) his or her intent at the time of the most serious attempt, (c> the actual medical threat to life following the most serious attempt. Individuals who had committed suicide were categorised as having an extreme degree of medical threat. Wherever possible, the interview data from the SADS-L were corroborated by information from hospital case notes and the patient’s general practitioner. In every case where the patient had died during the follow-up period, the death certificate was obtained and the cause of death ascertained (Lee and Murray, 1988). In examining the risk factors for suicidal behaviour, we grouped together those who had attempted or completed suicide; henceforth referred to as suicide ‘attempters’ (see Fig. 1). We hypothesised that the severity of depression, the presence of previous suicidal attempts, and certain other characteristics of the depression increase the risk of future suicidal behaviour. In addition, we hypothesised that a history of loss and personality abnormalities would also have a positive association with suicidal behaviour. These
113
Original
sample
Traced
(n = 89)
18 years later?
Yes (n = X8> I Alive?
No (n = 1)
I
I Yes (n = 65) I Interviewed by SADS-L?
r-----l
Yes (n = 56)
No (n = 9)
No (n = 23) I Suicide?
’
Yes (n = 5)
No (n = 181
I Attempted
suicide?
Yes (n = 24)
No (n = 32) Fig. 1. Composition
predictions were examined using Fisher’s exact test for the discrete variables and Student’s t-test for the continuous measures. Variables with a significant or near-significant effect in the univariate analysis were then entered into generalised linear models (McCullagh and Nelder, 1989) as predictor variables for the presence/ absence of suicidal behaviour; and the frequency, intent and medical threat of such behaviour. The prediction of the presence/absence, and the frequency of suicidal behaviour was performed with the program GLIM. For the former the logistic model was used, assuming that the outcome variable has a binomial distribution and is ‘linked’ to the predictors by a logit function. For the latter we used the log-linear model, assuming a Poisson distribution for the number of attempts and a log link function. The prediction of the intent and medical threat of attempts was performed by the LOGIST procedure of SAS, under the option for ordinal logistic regression. In each analysis a backward stepwise procedure was used so that variables whose deletion did not significantly decrease the fit of the model were removed.
OF sample.
Results The composition of the sample is shown in Fig. 1. Suicidal attempting was common with 24 of the 56 interviewed survivors (43%) making at least one attempt in the follow-up period (Table 1). To these 24 attempters were added the five individuals (6% of the total sample) who committed suicide. Thus, 29 attempters and 32 non-attempters formed the two comparison groups in the univariate analyses. The two groups did not differ significantly with regard to gender or social class. Similarly, there was no difference in the mean age of onset or the presence or absence of previous depression. Both severe dysphoria at the index admission and psychomotor retardation were positively associated with subsequent suicidal behaviour (P = 0.02 and 0.045 respectively, see Table 2). Historical information implicated previous brain injury as significant (P = 0.02). A history of alcoholism, past suicidal attempting and chronic physical illness were also associated with suicidal behaviour, although none of these reached statistical significance (P = 0.1). Classification into various de-
114
pressive subtypes was non-discriminatory as none of these, whether clinically or operationally defined according to RDC or DSM-III, showed any effect. The experience of loss was more common among suicide attempters (59%) as compared to the non-attempters (37.5%) (Table 2). When this loss was further subdivided into loss by death and by separation, the difference between suicide attempters and non-attempters was accounted for entirely by loss through separation; the former had more than twice the amount of loss than the latter. Loss by separation was associated with suicidal attempting (P = 0.045) whereas loss by death was not (P = 0.58). Against expectations, none of the results from the personality tests (EPI and LOI) administered when the patient had recovered showed any association with subsequent suicidal attempting nor did personality disorder diagnosed according to DSM-III (Table 2). As the combination of completers and attempters is questionable, the same analyses were performed excluding the five individuals who comTABLE
1
CHARACTERISTICS YEARS FOLLOW-UP
OF SUICIDAL
BEHAVIOUR
Frequency Number 0 1 2 3 4 5 6 7 8
ofattempts 32 8 4 4 3 0 1 2 2
Intent Not rated Minimal Serious Very serious Extreme Medical threat Not rated Mild Moderate Severe Extreme (death
3 9 I 4 1
by suicide)
2 6 10 6 5
IN 18
TABLE
2
PREDICTORS
OF SUICIDE
ATTEMPTS
Suicide -
Suicide +
DepresCe symptom Severe no dysphoria yes Retarded no yes Agitated no yes
32 0 27 5 26 6
24 5 18 11 20 9
Depressice subtypes Psychotic no yes DSM-III no melancholic yes RDC no bipolar yes no RDC secondary yes
20 12 18 14 21 4 27 4
14 15 13 16 25 4 24 5
Past history Previous suicidal attempts Family history of psychosis Family history of neurosis Previous brain damage Chronic physical illness History of alcoholism Loss by death Loss by separation
no yes no yes no yes no yes no yes no yes no yes no yes
20 12 27 5 31 1 32 0 32 0 32 0 25 7 27 5
13 16 22 7 26 3 24 5 26 3 26 3 23 6 18 11
no yes
21 11
21 8
Personality DSM-III personality disorder
Inoentory (on recovery of index illness) a EPI neuroticism 14.4 extraversion 12.1 20.7 LO1 symptoms traits 9.8 resistance 13.4 interference 12.8
(0.8) (1.0) (2.1) (1.0) (1.8) (2.6)
-
14.8 12.7 20.4 8.7 15.2 16.3
P (one tailed)
0.02 0.045 0.2
0.2 0.3 0.6 0.5
0.1 0.4 0.3 0.02 0.1 0.1 0.58 0.045
0.4
(0.3) (0.8) (1.7) (0.8) (2.0) (2.5)
0.8 0.6 0.9 0.4 0.5 0.3
’ Mean scores k SE.
pleted suicide. The results were broadly similar, as one might expect from the small number of suicide completers. The biggest change was that
115
the P-value for a history of alcoholism increased from 0.1 to 0.43, when those who had committed suicide were excluded. TABLE
3
GENERALISED HAVIOUR
LINEAR
MODELS
FOR
SUICIDAL
Backward logistic regression: presence/absence of suicidal attempts Variables removed Scaled deviance None 47.049 + Retardation 47.643 + Separation 50.373 + Brain damage 53.281 + Previous suicide attempts 55.621 Variables selected Coefficient 9.85 Severe dysphoria Chronic physical illness 9.31 Previous alcoholism 9.31
df 45 46 47 48 49 SE 27.36 33.02 33.02
Backward loglinear modelling: frequency of suicidal attempts Variables removed None + Retardation + Previous alcoholism + Brain damage + Chronic physical illness Variables selected Severe dysphoria Separation Previous suicide attempts
df 40 41 42 43 44 SE 0.26 0.25 0.30
Scaled deviance 82.116 82.314 83.693 85.813 88.290 Coefficient 1.35 0.56 1.24
Backward ordinal logistic regression: intent of suicidal attempts Variables removed Scaled deviance 77.61 None 77.64 + Retardation 80.30 + Chronic physical illness + Previous suicidal attempts 82.85 Coefficient Variables selected - 9.46 Previous alcoholism Separation 1.53 Severe dysphoria 3.31 Brain damage 1.59 Backward ordinal logistic regression: medical threat of suicidal attempts Variables removed Scaled deviance 113.85 None 114.57 + Separation 115.29 + Severe dysphoria + Brain damage 117.21 + Previous alcoholism 119.72 Variables selected Coefficient Previous suicidal attempts 1.74 1.69 Retardation Chronic physical illness 2.85
BE-
df 40 41 42 43 SE
_ 0.69 1.12 0.74
df 45 46 47 48 49 SE 0.62 0.62 1.27
The following seven variables - chronic physical illness, psychomotor retardation, severity of mood disturbance, past attempting, history of alcoholism, of separation and of brain damage were selected for further exploration with generalised linear models (Table 3). The presence or absence of suicidal behaviour was significantly predicted by severe dysphoria, past alcoholism and chronic physical illness. The large standard errors of the parameter estimates are due to the fact that few individuals have these characteristics, but those who do are all attempters. For this reason, the odds ratios for these effects cannot be estimated accurately, even though we have evidence that they are greater than 1. In contrast to the presence or absence of suicidal behaviour, the frequency of attempting was significantly related to severe dysphoria, past suicidal attempts, and separation. Similarly, the predictors of the degree of intent and medical threat were different: intent was predicted by severe dysphoria, brain damage, past alcoholism and separation; and threat by chronic physical illness, past suicidal attempts and psychomotor retardation. The interpretation of the coefficients is made easier by taking their exponents, e.g., having severe dysphoria increases the number of attempts on average by a factor of e’.35 or 3.86. The model for predicting the presence/ absence of suicidal behaviour fitted the data fairly well (scaled deviance = 55.6, df = 49, P > 0.2), but the fit of the other models was poor. Discussion Despite an extensive literature on suicide, few long-term prospective studies have attempted to identify risk factors (Beck and Steer, 1989). Although our index data were not collected specifically to address the question of future suicidal behaviour, the problem of retrospective bias is overcome by concentrating solely on these data. However, the information on the suicidal attempt is retrospective and hence is subject to recall error. For instance, the measurement of suicidal intent is especially difficult, and therefore one should be cautious in interpreting the results. Certain other limitations also need to be acknowledged. Firstly, we grouped together suicide
116
attempters and completers. As these may represent two different populations Kreitman, 1977), some may question their combination. However, we have shown that the exclusion of suicide completers did not change the results significantly, except for alcoholism, although this is not surprising in view of the small number of suicide completers in the sample. Secondly, in making 23 comparisons, there is a danger of finding spurious relationships. While this is a valid consideration, an examination of our data (Table 2) shows that the 23 comparisons produced four with a P-value of < 0.05 and three further comparisons of P < 0.1, figures which are greater than the one or two results of significance which may be expected to arise by chance. Nevertheless, caution should be exercised in interpreting these results as some may be falsely positive. Thirdly, the numbers in some of the cells are small, so that statistical power is limited. This is a particular problem for the analysis of the subtyping data where our failure to find an effect may have been due to small sample sizes. These limitations aside, our results indicate that among patients hospitalised with depression, subsequent suicidal behaviour was extremely common, with almost half the sample (48%) either attempting or completing suicide over the 18 years follow-up. Moreover, this is not an isolated result as a similar study by Andrews et al. (1990) has produced almost identical figures for completed suicide, 11 of 193 patients (5.7%) followed up for 15 years committing suicide. What features, therefore, led patients to engage in subsequent suicidal behaviour? There were few surprises among the variables showing a positive association with suicidal behaviour in the univariate analyses. As many previous investigations have relied on cross-sectional data, however, similar findings from our longitudinal design offer important confirmation. Previous work already identifying severity of depression (Bulik et al., 1990), psychomotor retardation (Barraclough and Pallis, 1975) and alcoholism (Beck and Steer, 1989) as having important associations with suicidal behaviour is supported by our data. Further subtyping the index depressive episode failed to show any relationship with such behaviour, a negative finding again supported by
a recent prospective investigation (Fawcett et al., 1987). Our finding that loss by separation but not loss by death was associated with subsequent suicidal behaviour also replicates previous findings (Crook and Raskin, 1975; Bronisch and Hecht, 1987). An explanation for this differential effect may be that it is family instability and discord prior to the loss that is important in leading to subsequent suicide behaviour (Adam et al., 1982) and that such instability is more common in loss by separation. The negative results from the personality inventories and from the DSM-III classification of personality were surprising. This may be a reflection of the inventories used which may not identify the personality types (often aggressive, impulsive or borderline) associated with suicidal behaviour (Angst and Clayton, 1986). Another possible reason for our failure to find any effect of personality is that we have examined a depressed sample, as Bronisch and Hecht (1987) also failed to establish a relationship between abnormal personality and suicidal behaviour in depressed patients, while Casey (1987) found an apparent relationship which disappeared after controlling for the severity of depression. What of our more ambitious aim of eliminating redundant influences by generalised linear modelling? With the dichotomy of the presence or absence of suicide attempt, it was possible to reduce the number of variables with a significant effect to three: severe dysphoria, alcoholism and chronic physical illness. However, this dichotomisation is simplistic as suicidal activity itself is not an all-or-none phenomenon; rather it represents a diverse spectrum of behaviours. That this is so has previously been demonstrated by the differential association of certain predictors with the different aspects of suicidal behaviour (Plutchik et al., 1989). In our study, severe dysphoria and separation were most strongly associated with frequency of attempting, but they had the least effect as regards medical threat (i.e., the more severe and sometimes fatal suicidal activity). Conversely, psychomotor retardation had an effect for medical threat but very little for frequency of attempting. Thus, there is a suggestion that the features which lead individuals to make many attempts do not predict completed suicide and
117
vice versa (Kreitman, 1977). These differences in the predictors are also reflected in our finding only a moderate correlation (Spearman’s p = 0.59, P < 0.003) between frequency and medical threat in the surviving attempters. These speculations need to be tempered by recognising the limitations of the study. As one might expect, the model with the best fit was the presence/absence of suicidal behaviour as this was the simplest to predict. The models for frequency, intent and threat were more complex and consequently had a relatively poorer fit. This lack of predictive power may partly be due to the sole reliance on index variables, since in a follow-up of 18 years such influences can best be regarded as predisposing factors. Their influence might therefore have been considerably strengthened if we had been able to take additional later developments into account. In some respects, depression itself may be regarded as a predisposing factor leading to suicidal behaviour through the development of additional complications. Psychiatric complications were common in this series (Lee and Murray, 1988). For example, the number of individuals with alcoholism increased from 3% at index to 10% some 18 years later. These additional cases increased the statistical significance of the relationship between alcoholism and ever attempting suicide from P = 0.1 to P = 0.06. Thus depression itself may lead to suicide but in addition, it provides fertile ground for the develapment of other social and psychiatric complications which bring in their train further risks of suicidal behaviour. Acknowledgements The authors would like to acknowledge the contributions of Professors R.E. Kendell and G. Brown and colleagues whose initial assessment of the sample made this report possible. Financial support was provided by the Mental Health Foundation, the Bethlem and Maudsley Fund, the Wellcome Trust and the Medical Research Council. References Adam, K.S., Bouckoms, A. and Streiner, loss and family stability in attempted Psychiatry 39, 1081~1085.
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