Suicidal Ideation and Later Suicide

To the Editor: In the December 2011 issue of the Journal, Posner et al. (1) state that “studies of risk factors predicting suicide consistently suggest that suicidal ideation and a history of suicide attempts are among the most salient risk factors for suicide.” We agree that there is strong evidence of a relationship between suicide attempts and subsequent suicide, but the association between expressed ideas of suicide and suicide is less clear.

The authors cite four papers supporting the presence of an association. The first reported mortality among suicide attempters but did not mention suicidal ideation (2). The next two found that high scores on the Scale for Suicide Ideation were associated with later suicide (3, 4). However, some items on this scale describe suicidal behavior rather than suicidal ideation, and it is the behavior items that are strongly associated with suicide (5). The fourth study found an association between suicidal ideation and suicide attempts, but it did not consider completed suicide (6).

In fact, two systematic meta-analyses have found weak associations between suicidal ideation and suicide. The first found that a modest association between suicide and suicidal ideation expressed by psychiatric inpatients might have been because of publication bias (7). Suicidal ideation did not independently predict inpatient suicide when depressed mood and previous suicide attempts were also considered (8). The second study found that suicidal ideas expressed in the hospital were weakly associated with suicide after discharge (9). We agree that there is a need to clarify the definitions of suicidal ideation and behavior. However, the presence of suicidal ideation, in the absence of a suicide attempt, has not been firmly established as a risk factor for suicide.