Multidimensional item response theory models yielded good fit and reliable scores for the Short Form-12 questionnaire.

Objectives: To propose a multidimensional item response theory (MIRT) scoring system for the Short Form 12 (SF-12) with good psychometric properties in terms of fit and reliability. Study Design and Settings: Two models, indicating physical (PCS) and mental component summary (MCS) dimensions, were fitted to SF-12 data from the European Study of the Epidemiology of Mental Disorders, a representative sample from European adult general population (n521,425; response rate561.2%). Goodness of fit, information, reliability, and agreement of individual scores were compared with the classical SF-12 and RAND-12 algorithms. Results: The bidimensional response process (BRP) model, where all items are indicators of both dimensions, yielded the best fit (root mean square error of approximation50.057, comparative fit index50.95, and TuckereLewis index50.94), and highly agreed with PCS and MCS scores from the SF-12 (intraclass correlation coefficients of 0.92 and 0.88, respectively) and RAND-12 (0.88 and 0.95). Regarding reliability, the BRP yielded 0.75 and 0.77 (PCS and MCS, respectively), greater than SF-12 (0.65 and 0.66) and RAND-12 (0.65 and 0.67). As indicated by scale linking, MIRT scores can be interpreted similarly to the classical scores. Conclusion: The MIRT models showed a clear construct structure for the PCS and MCS dimensions, defined by functional and role limitation content. Results support the use of SF-12 MIRT-based scores as a valid and reliable option to assess health status. © 2013 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]