Comparability of interview- and self-administration of the Functional Assessment of Cancer Therapy-General (FACT-G) in english- and Spanish-speaking ambulatory cancer patients

BACKGROUND:: Flexibility is important in choosing methods and modes of questionnaire administration, to accommodate the needs of patients with diverse linguistic, cultural, educational, and functional skills. OBJECTIVE:: To investigate the extent to which 2 different modes (interview- vs. self-administration) yielded comparable estimates of health-related quality of life (HRQL) as measured by the Functional Assessment of Cancer Therapy-General (FACT-G). PARTICIPANTS:: English- (n ≤ 739) and Spanish-speaking (n ≤ 456) ambulatory cancer patients. RESEARCH DESIGN:: Patients were randomly assigned to interview- or self-administration of questionnaires, stratified by site, language, and race/ethnicity. A 3-phase analytic strategy was implemented: (1) confirmatory factor analysis to confirm unidimensionality of each FACT-G subscale; (2) 2 techniques to evaluate differential item functioning across modes; and (3) multivariable regression to compare mean HRQL scores across modes. RESULTS:: Confirmatory factor analysis model fit indices provided good support for unidimensionality across all 4 language/mode groups. Three of 27 items demonstrated statistically significant mode differential item functioning in each language. There were no statistically significant or minimally important mode effects on mean HRQL outcomes, with or without adjusting for other factors. CONCLUSIONS:: Among both English- and Spanish-speaking ambulatory cancer patients, the FACT-G can be administered by either interview- or self-administration, without concern for significant mode effects on the data. Results may not be generalizable to patients with greater disease severity or those with low literacy.