Psychometric properties of the 30-item version general health questionnaire in Japanese.

Psychometric properties of the 30-item General Health Questionnaire (GHQ-30) were explored using the Japanese data collected in various settings. A six- or seven-factor structure emerged for the entire sample and each gender and age-group divided into a 10-year interval. The factors were highly identical across the subsamples. The main four factors showed a high agreement with those of UK and Hong Kong studies: approximately 80% of the items were similarly allocated to factors. However, the response endorsement of two "loss of positive attitude" items was much common regardless of the score level. These items counted up approximately one-fourths of the score, so that these items made the score spuriously higher. According, a question arose as to whether these items should be included in the scale for its use in Japanese.