Developing a shortened quality of life scale from Persian version of the WHOQOL-100 using the rasch analysis

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 ques-tionnaire,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 sam-pled. 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,respective-ly. 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 cur-rent health status groups (p<0.001). we eliminated 67 persons for under-fitting,38 items for category and/or thresh-old 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. © 2015,iranian journal of public health. all right reserved.