LAUSR

OBJECTIVE This study introduces a new method to establish clinical thresholds for multi-item tests, based on item response theory (IRT), as an alternative to receiver operating characteristic (ROC) analysis. The performance of the IRT method was examined and compared with the ROC method across multiple simulated datasets and in a real dataset. STUDY DESIGN AND SETTING Simulated datasets (sample size: 1000) varied in means and variability of the test scores and the prevalence of disease. The true clinical threshold was defined as a predetermined location on the latent trait underlying the questionnaire, with its corresponding expected test score. The real dataset (sample size: 295) comprised Hospital Anxiety Depression Scale depression scores and DSM-IV major depressive disorder (MDD) diagnoses. RESULTS The IRT method recovered the clinical thresholds without bias, whereas the ROC method identified thresholds that were biased by the prevalence of disease. Mild MDD was clinically diagnosed in 23%, moderate MDD in 12%, and severe MDD in 14% of the participants. The IRT method identified the following HADS depression score thresholds for mild, moderate and severe MDD: 10.7, 13.2 and 15.1 respectively. CONCLUSION The new IRT method identifies clinical thresholds that are unbiased by disease prevalence.