Effects of method of translation of patient-reported health outcome questionnaires: a randomized study of the translation of the Rheumatoid Arthritis Quality of Life (RAQoL) Instrument for Sweden.

AIMS To compare two versions of a questionnaire translated using forward-backward (FB) translation and dual-panel (DP) methodologies regarding preference of wording and psychometric properties. METHODS The Rheumatoid Arthritis Quality of Life instrument was adapted into Swedish by two independent groups using FB and DP methodologies, respectively. Seven out of thirty resulting items were identical. Nonidentical items were evaluated regarding preference of wording by 23 bilingual Swedes, 50 people with rheumatoid arthritis (RA), and 2 lay panels (n = 11). Psychometric performance was assessed from a postal survey of 200 people with RA randomly assigned to complete one version first and the other 2 weeks later. RESULTS Preference did not differ among the 23 bilinguals (P = 0.196), whereas patients and lay people preferred DP over FB item versions (P < 0.0001). Postal survey response rates were 74% (FB) and 75% (DP). There were more missing item responses in the FB than the DP version (6.9% vs. 5.6%; P < 0.0001). Floor/ceiling effects were small (FB, 6.1/0%; DP, 4.4/0.7%) and reliability was 0.92 for both versions. Construct validity was similar for both versions. Differential item functioning by version was detected for five items but cancelled out and did not affect estimated person measures. CONCLUSIONS The DP approach showed advantages over FB translation in terms of preference by the target population and by lay people, whereas there were no obvious psychometric differences. This suggests advantages of DP over FB translation from the patients' perspective, and does not support the commonly held view that FB translation is the "gold standard."