RESUMO
Research on quality of life (QOL) in Thailand is still in its developing stages and requires cross-culturally valid QOL questionnaires to appropriately assess QOL as an endpoint in research and clinical trials. The English-language version of the FACT-G (Version 4) questionnaire was translated into Thai using an iterative forward-backward translation process. To determine if this instrument could cross a broad cultural divide and be used in Thailand, the reliability and validity of its Thai version was studied. The translated questionnaire was administered to 364 cancer patients. In evaluating its psychometric properties, internal consistency by Cronbach's alpha and test/retest reliability measured by Spearman rank-correlation coefficients were used. Cronbach's alpha coefficient ranged from 0.75 to 0.90. Spearman rank-correlation coefficient value for global QOL was 0.80. Validity was checked using two methods: factor analysis and known-groups comparison. Known-groups comparison analysis showed discrimination between subgroups of patients differing in clinical status as defined by disease stage (stage I/II vs stage III/IV, p < 0.001), treatment status (active treatment vs no treatment, p < 0.05), and financial burden (yes vs no, p < 0.001). In conclusion, the finding of this study indicate that the Thai version of the Functional Assessment of Cancer Therapy-General (FACT-G) is a reliable and valid measure of quality of life in cancer patients and can be used in clinical trials and studies of outcomes research in oncology.