The effect of postal questionnaire burden on response rate and answer patterns following admission to intensive care: a randomised controlled trial.

Background: The effects of postal questionnaire burden on return rates and answers given are unclear following treatment on an intensive care unit (ICU). We aimed to establish the effects of different postal questionnaire burdens on return rates and answers given.
Methods: Design: A parallel group randomised controlled trial. We assigned patients by computer-based randomisation to one of two questionnaire packs (Group A and Group B).
Setting: Patients from 26 ICUs in the United Kingdom.
Inclusion Criteria: Patients who had received at least 24 h of level 3 care and were 16 years of age or older. Patients did not know that there were different questionnaire burdens. The study included 18,490 patients. 12,170 were eligible to be sent a questionnaire pack at 3 months. We sent 12,105 questionnaires (6112 to group A and 5993 to group B).
Interventions: The Group A pack contained demographic and EuroQol group 5 Dimensions 3 level (EQ-5D-3 L) questionnaires, making four questionnaire pages. The Group B pack also contained the Hospital Anxiety and Depression Score (HADS) and the Post-Traumatic Stress Disorder Check List-Civilian (PCL-C) questionnaires, making eight questionnaire pages in total.
Main Outcome Measure: Questionnaire return rate 3 months after ICU discharge by group.
Results: In group A, 2466/6112 (40.3%) participants responded at 3 months. In group B 2315/ 5993 (38.6%) participants responded (difference 1.7% CI for difference 0-3.5% p = 0.053). Group A reported better functionality than group B in the EQ-5D-3 L mobility (41% versus 37% reporting no problems p = 0.003) and anxiety/depression (59% versus 55% reporting no problems p = 0.017) domains.
Conclusions: In survivors of intensive care, questionnaire burden had no effect on return rates. However, questionnaire burden affected answers to the same questionnaire (EQ-5D-3 L).
Trial Registration: ISRCTN69112866 (assigned 02/05/2006).