Effect of order of administration of health-related quality of life interview instruments on responses

Purpose: To determine the effect on patient responses from the order in which the generic health-related and vision-targeted instruments are administered in a set of randomized clinical trials of intraocular surgery. Patients and methods: Patients who agreed to enroll in the Submacular Surgery Trials (SST) completed baseline quality of life interviews prior to random assignment to surgery or observation. Interviews were conducted by trained interviewers located at the SST Coordinating Center, via a computer-assisted telephone interview system that randomly assigned the order of instrument administration. Either the generic health-related instruments were administered first, the SF-36 Health Survey (SF-36) followed by the Hospital Anxiety and Depression Scale (HADS), followed by the vision-targeted instruments, National Eye Institute-Vision Function Questionnaire (NEI-VFQ) followed by the SST-Vision Preference Value Scale, or the vision-targeted questions were asked first, followed by the generic health instruments. The four instruments have 25 subscales total. Results: Of the 1015 patients enrolled in the SST, 992 patients had all four instruments administered in random order: 483 (49%) patients responded to the generic instruments first and 509 (51%) patients responded to the vision-targeted instruments first. Order of administration produced significantly different scores for three health status subscales: SF-36 mental health, HADS depression and HADS anxiety (p <= 0.05, Wilcoxon rank sum test). Conclusions: Overall, the order of administration did not have a large effect on responses to the baseline interviews in this study. However, three mental health subscales were affected by order, though the order effect was small in magnitude. When the generic health instruments followed the vision-targeted instrument the HADS depression and anxiety scores were higher and the SF-36 mental health scores were lower, both suggesting poorer mental health status. Thus, the order of administration in other settings in which both a generic health-related instrument and a condition-targeted instrument are used may be decided based on individual study goals and priorities but order of administration should be consistent throughout the study.