Abstract: Objective According with Chinese legal system, to develop a competency to stand trial rating scale in offenders with mental disorders. Methods Proceeding from the juristical elements, 15 items were extracted and formulated a preliminary instrument named the competency to stand trial rating scale in offenders with mental disorders. The item analysis included six aspects, which were critical ratio, item-total correlation, corrected item-total correlation, α value if item deleted, communalities of items, and factor loading. The Logistic regression equation and cut-off score of ROC curve were used to explore the diagnostic efficiency. Results The data of critical ratio of extreme group were 18.390-46.763; item-total correlation, 0.639-0.952; corrected item-total correlation, 0.582-0.944; communalities of items, 0.377-0.916; and factor loadings, 0.614-0.957. Seven items were included in the regression equation and the accuracy of back substitution test was 96.0%. The score of 33 was ascertained as the cut-off score by ROC fitting curve, the overlapping ratio compared with the expertise was 95.8%. The sensibility and the specificity were 0.938 and 0.966, respectively, while the positive and negative likelihood ratios were 27.67 and 0.06, respectively. Conclusion With all items satisfied the requirement of homogeneity test, the rating scale has a reasonable construct and excellent diagnostic efficiency.

Key words: forensic psychiatry, mental disorders, rating scale, competency to stand trial