To the Editor:

We read with great interest the article by Dr. Davidson et al. The methodological procedures and results of this study are of special interest to our research team as we have extensively studied predictive markers of this disorder.

Dr. Davidson and colleagues commented that a strength of the design of their screening tool is the use of both cognitive and behavioral measures to identify vulnerability for schizophrenia. Gal (1) stated that these screening instruments are highly reliable and valid predictors of the constructs that they purport to measure. However, the criterion used in validation is based on the "soldier’s rank upon his discharge from the compulsory service period" (1, p. 80). This leaves our research team concerned about the appropriateness of the use of this measure in the present study. Although this instrument was documented to be a valid predictor of rank, we are uncertain of its utility in predicting IQ. Furthermore, although Dr. Davidson et al. commented on the similarities between the subtests of the WAIS and the subtests of their cognitive battery, no psychometric data were provided by Gal establishing the measures’ convergent validity.

Dr. Davidson and colleagues established a cutoff of the lowest two quintiles in the social functioning scale for accurately predicting membership in the patient group. These cutoffs have no apparent statistical or conceptual validity, as the authors failed to indicate whether patients in the second quintile differed statistically from patients falling into the third quintile. This overlap between the second and third quintiles for the patient group reduced the sensitivity in predicting behavioral markers for schizophrenia. Moreover, it is unclear how the authors determined this cutoff and if it is applied to the other measures in this study. Assuming that Dr. Davidson et al. applied a similar method in evaluating the other measures, we believe that this application is misleading in identifying subtle predictors of schizophrenia. For example, with "organizational ability" and "interest in physical activity," the extreme rating of "1" robustly distinguishes between groups; however, in ratings 2–5, the differences are not consistently evident. It appears that only extremely small differences between these constructs may be useful as markers in predicting vulnerability to developing schizophrenia.

In summary, we agree with Dr. Davidson and colleagues’ conclusion that abnormalities in social functioning, organizational ability, interest in physical activity, individual autonomy, and intellectual functioning can identify individuals who will manifest schizophrenia in the future. The degree of overlap between patients and nonpatients and the absence of psychometric support for the study’s measures reduce the sensitivity of this model in predicting predisposition to schizophrenia.