Tehran University of Medical Sciences Iranian Journal of Public Health 2251-6085 44 4 2015 04 15 522 34 Kamran Yazdani Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Saharnaz Nedjat Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran AND Knowledge Utilization Research Center, Tehran University of Medical Sciences, Tehran, Iran. Masoud Karimlou Dept. of Statistics and Computer, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran. Hojjat Zeraati Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Kazem Mohammad Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Akbar Fotouhi Dept. of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 14 Background: Few studies use modern approaches to develop a quality of life (QOL) questionnaire with acceptable construct validity, especially in Iran. Our main objective was to construct a new validated and uni-dimensional questionnaire, based on WHOQOL-100, using the Rasch analysis. Methods: In a population-based, cross-sectional study in 2007, 500 Tehran residents aged≥18 were randomly sampled. The Persian version of WHOQOL-100 was used to measure the participants' QOL. After using targeting and person fit analysis, we performed category/threshold ordering, item fit, and differential item functioning analyses, in succession. We used outfit or infit statistics>1.5 and <0.5 for detecting underfit and overfit items/persons, respectively. We also deleted items with disordered category and/or threshold. Person Separation Index and test reliability were also calculated in the datasets. Results: Male to female ratio was 0.98 and the mean age (SD) of participants was 35.1 (12.8) years. Initial analyses showed significant differences in quality of life between age groups (P=0.002), educational levels (P=0.001), and current health status groups (P<0.001). We eliminated 67 persons for under-fitting, 38 items for category and/or threshold disordering, 6 items for under-fitting, and 26 items for item bias. Test reliability for the final 30-item scale was 0.89. Conclusion: We prepared a shortened version of the WHOQOL-100 that is single construct, uni-dimensional and free of item bias or any disordering, according to the Rasch model. https://ijph.tums.ac.ir/index.php/ijph/article/view/3592 https://ijph.tums.ac.ir/index.php/ijph/article/download/3592/3267