Development of the Quality of Life Questionnaire (SF-36) for Patients with β-Thalassemia Major and β-Thalassemia Intermedia Based on Extended Rasch Analysis

Abstract

The quality of life (QoL) questionnaire (SF-36) contains 36 questions in eight subscales. It requires much time to fill in by the respondent. The objective of this study was to use Rasch models to develop a questionnaire that brings the desired outcome of the QoL of people. Therefore, a new questionnaire was provided that is more motivating and time-saving for respondents than SF-36. The QoL of life assessment data of 325 β-thalassemia major (β-TM) and β-thalassemia intermedia (β-TI) patients in Kerman, Iran, was used as research data. In this study, the appropriate questions were classified in a limited dimensional framework using the exploratory factor analysis (EFA). The correctness of the factor structure was assessed by confirmatory factor analysis (CFA). The quality of the questions was evaluated by Rasch modeling [partial credit model (PCM)] and item analysis to ensure the validity and reliability of the questionnaire. Finally, the Pearson correlation coefficient was used to compare the new questionnaire with the previous one. This process resulted in the development of a new questionnaire with five subscales and 20 questions. The construct validity of the new questionnaire was good. The reliability index of the questionnaire was 0.75, and the Pearson correlation coefficient between the QoL scores gained from the previous and the new questionnaires was 0.93 that indicates the strength of the correlation. The use of Rasch analysis in this study resulted in the development of a new reliable and valid questionnaire.