Psychiatry Research 209 (2013) 746

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Psychiatry Research

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DOI

journal homepage: www.elsevier.com/locate/psychres

Letter to the Editor

Suicide ideas and immediate suicide risk

To the Editors:

Britton et al. (2012) report the characteristics of 381 suicidevictims who had contact with veterans medical services in the lastyear of their lives. They found that thoughts of committing suicidewere disclosed by seven of 67 patients who committed suicidewithin a week of contact with health services and by 15 of the 381patients who committed suicide in the following year. The authorsstated that, “the assessment of suicidal ideation is critical toidentify veterans at immediate risk [of suicide].”

However, the article did not address a methodological limita-tion arising from the absence of data about the proportion ofpatients with suicide ideas who did not commit suicide. As a resultwe cannot be sure of the base rate of suicide in their patient groupor the potential role of suicide ideas in distinguishing betweenthose who will and will not commit suicide. According to the datathat was provided, the incidence of suicide within a week ofcontact was 17.6% (67/381) of the incidence of suicide within ayear of contact. We also know that the sensitivity of reportedsuicidal ideation for suicide was 10.4% (7/67) within the next weekand was 3.9% (15/381) in the next year. Using this data, a generousestimate of the positive predictive value of suicide ideas can becalculated if we assume a very high base rate of one in 1000veterans committing suicide within a year of contact with medicalservices, and an unrealistically high specificity of suicidal ideas forsuicide of 95% (Large et al., 2011a, 2011b). With these highlyfavorable assumptions, it can be estimated that one in 2732(0.04%) of the patients who express suicidal ideas will commitsuicide within the next week and one in 1282 (0.08%) will commitsuicide within a year.

This illustrates two major limitations to suicide risk assess-ment. First, the low base rate of suicide means that the proportionof patients who commit suicide will always be low, even in groupsof people considered to be at increased risk (Large et al., 2011a,2011b). Second, although clinical indicators such as suicide ideasmight be more strongly associated with subsequent suicide in the

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short-term than the long-term, as was the case in the recent study,the lower base rate over a short period of follow up means that thepositive predictive value of short-term suicide risk assessment islikely to be lower than the positive predictive value over a longerperiod.

In their introduction, the authors discuss the well-knownfinding that many patients who commit suicide have had contactwith health services shortly before their death. The data presentedby Britton and associates suggest that almost a fifth of the suicideswithin a year of contact occur in the first week, which representsan odds ratio of suicide of over 10 for this period compared to theremaining 51 weeks. Health care providers face a very realproblem in their attempts to prevent suicide. Although peoplewho attend medical and psychiatric services are at a higher risk ofsuicide in the short term than the general population, the low baserate and the non-specific nature of established risk factors severelylimits our current ability to predict which patients will go on tocommit suicide.

References

Britton, P.C., Ilgen, M.A., Rudd, M.D., Conner, K.R., 2012. Warning signs for suicidewithin a week of healthcare contact in Veteran decedents. Psychiatry Research200 (2–3), 395–399.

Large, M., Smith, G., Sharma, S., Nielssen, O., Singh, S.P., 2011a. Systematic reviewand meta-analysis of the clinical factors associated with the suicide ofpsychiatric in-patients. Acta Psychiatrica Scandinavica 124 (1), 18–29.

Large, M.M., Ryan, C.J., Singh, S.P., Paton, M.B., Nielssen, O.B., 2011b. The predictivevalue of risk categorization in schizophrenia. Harvard Review of Psychiatry 19(1), 25–33.

Matthew M. Large n

School of Psychiatry, University of New South Wales, Sydney, NSW,Australia

Olav B. NielssenClinical Research Unit for Anxiety and Depression, St. Vincent's

Hospital, Sydney, AustraliaDiscipline of Psychological Medicine, University of Sydney, Australia

n Correspondence to: Mental Health Services, Prince of Wales Hospital, BarkerSt., Randwick 2031, NSW, Australia.E-mail address: mmbl@bigpond.com