These data show that the MHI-5 and MHI-3 scores were each correlated with the ZSDS score and had good screening accordance with the ZSDS in the general population of Japan. We also found that the MHI-3 performs almost as well as the MHI-5. The best-performing single item was the one asking about "feeling downhearted and blue," which was also the case in the US . The usefulness of the MHI-5 is consistent with results of a study done in the US . Each scale and each item performed best as a detector of severe depressive symptoms, but each also contributed some information even for detecting moderate and mild depressive symptoms (Table 3). Both scales performed better than did any item alone.
Because prevalence affects positive predictive value, the latter was lowest for severe depressive symptoms and was highest for mild, moderate, and severe depressive symptoms (Table 4). For all levels of symptom severity, the positive predictive values of the MHI-3 were similar to those of the MHI-5, and for severe depressive symptoms they were nearly identical (10.8% and 10.4%) (Table 4).
A previous study showed that the prevalence of mood disorders (major depression, bipolar disorders, and dysthymia) as measured using the DSM criteria in Japanese people 20 years old and older was 3.1% . On the other hand, 37% of the sample in the present study had mild, moderate, or severe depressive symptoms as measured using the ZSDS. People in whom depression is diagnosed using the DSM criteria are probably only a small number of those who report at least some depressive symptoms. In a previous study that also used the ZSDS, the prevalence of mild depressive symptoms among Japanese male workers was 45% , which is similar to that in our study.
In addition to its performance as shown in the present ROC analysis, an advantage of the MHI-5 may be the fact that it is part of the SF-36. The reason is that the possibility of a Hawthorne-type effect (i.e. an effect on study participants that results from their knowing that they are being studied) can be an obstacle to screening for depressive state. Specifically, the subjects' responses on a mental-health screening instrument may be affected by their knowledge that they are subjects in a study of mental health. Embedding the mental-health screening instrument in a more general survey, as the MHI-5 is embedded in the SF-36, could help minimize any such effect.
While the results of this study may be useful for public-health purposes, surveys done in primary-care settings could provide information that is more directly applicable to clinical work. Also, it should be kept in mind that ZSDS scores alone cannot be used to diagnose clinical depression. Studies using psychiatrist-diagnosed depression in addition to ZSDS scores would provide further information about the utility of the Japanese version of the MHI-5.
Another limitation is that the data set was obtained from a 1995 survey. Further studies are needed to confirm the performance of the MHI-5 and MHI-3 using data obtained in recent years.
In conclusion, the MHI-5 and MHI-3 scores were correlated with the ZSDS score, and can be used to identify people with depressive symptoms in the general population of Japan.