Is it valid to measure suicidal ideation by depression rating scales?

OBJECTIVE: To date, most researchers rely on suicidal items of scales primarily designed to measure depression severity to capture suicidal ideation (SI). This study aims at investigating how well the suicide item of the clinician rated Hamilton Scale for Depression (HAM-D) and principal factors derived from this scale correlate with SI scores derived from a well validated measure of SI: the Beck's scale for SI (SSI).
METHOD: 281 suicide attempters consecutively hospitalized between 2007 and 2009 were assessed by using the SSI, the HAM-D and the self-report Beck Depression Inventory (BDI). Principal Component Analysis (PCA) was computed to extract main factors. Correlations between these factors, BDI's and HAM-D's suicide items and the SSI scores were then computed.
RESULTS: Three components were derived from the PCA. Factor 2 showed a major loading for the HAM-D suicide item. Both the HAM-D suicide item and Factor 2 positively correlated with the SSI total score (both p<0.00001). Moreover, the BDI suicide item highly correlated with the Factor 2 (p<0.001) and the SSI total score (p<0.00001). Finally, the HAM-D suicide item correlated significantly with the number of suicide attempts (p=0.0001) and the age at the first attempt (p=0.002). LIMITATIONS: Our sample was heterogeneous and future studies should refine the taxonomy of the suicidal behavior in specific sub-populations. The study design was cross-sectional and replication in a prospective study is needed.
CONCLUSION: These findings suggest that the use of a single suicide item or a dimensional factor derived from a depression scale might be a valid approach to assess the suicidal ideations. Moreover, the results suggest that clinician rated scales as well as self-report questionnaires are equally valid to do so.