When less is more: reducing redundancy in mental health and psychosocial instruments using Item Response Theory

BACKGROUND: There is a need for accurate and efficient assessment tools that cover a range of mental health and psychosocial problems. Existing, lengthy self-report assessments may reduce accuracy due to respondent fatigue. Using data from a sample of adults enrolled in a psychotherapy randomized trial in Thailand and a cross-sectional sample of adolescents in Zambia, we leveraged Item Response Theory (IRT) methods to create brief, psychometrically sound, mental health measures. METHODS: We used graded-response models to refine scales by identifying and removing poor performing items that were not well correlated with the underlying trait, and by identifying well-performing items at varying levels of a latent trait to assist in screening or monitoring purposes. RESULTS: In Thailand, the original 17-item depression scale was shortened to seven items and the 30-item Posttraumatic Stress Scale (PTS) was shortened to 10. In Zambia, the Child Posttraumatic Stress Scale (CPSS) was shortened from 17 items to six. Shortened scales in both settings retained the strength of their psychometric properties. When examining longitudinal intervention effects in Thailand, effect sizes were comparable in magnitude for the shortened and standard versions. CONCLUSIONS: Using Item Response Theory (IRT) we created shortened valid measures that can be used to help guide clinical decisions and function as longitudinal research tools. The results of this analysis demonstrate the reliability and validity of shortened scales in each of the two settings and an approach that can be generalized more broadly to help improve screening, monitoring, and evaluation of mental health and psychosocial programs globally.