Pre-contact by telephone increases response rates to postal questionnaires in a population of stroke patients: an open ended randomized controlled trial

BACKGROUND: A follow-up study on a cohort of stroke patients through a postal survey questionnaire 3 and 12 months after discharge from hospital was performed. The response rate at 3-months follow-up was lower than desired, and pre-contact by phone as a measure for increasing the response rate at 12 months was studied. METHODS: The study design was a randomized controlled trial on a cohort of 3 months follow-up-non-responders where the intervention group was pre-contacted with an aim to obtain an informal ’consent to receive’ the questionnaire before the 12-months survey was mailed, and the control group was not. The primary outcome was 45 days response rate; secondary outcome was 365 days response rate. The main analysis followed the intention to treat principle. A secondary, per-protocol analysis (i.e. subjects who were not reached by phone were reassigned to the control group) is included. Also included is a rudimentary cost-utility analysis, where we estimated the cost per additional response. RESULTS: Of the 235 subjects, 116 were randomized to the intervention group and 119 to the control group. 10 were excluded due to death (7 in the IG and 3 in the CG), 6 due to dementia (3 in the IG and 3 in the CG), and 2 (1 in the IG and 1 in the CG) for other reasons. The primary outcome was a response rate of 42.9 % in the intervention group, and 26.8 % in the control group, giving p =0.014, with estimated OR of 2.04 (95 % CI [1.16,3.64]). The secondary outcome had p =0.009 with OR 2.10 (95 % CI [1.20,3.70]). The as-per-protocol analyses gave stronger results with p =0.001 and p =0.003, respectively. The cost-utility analysis gave a time cost of 1 working hour per additional response. CONCLUSIONS: The results are in line with previous research, and show that pre-contact has a positive effect on response rate also for a population of elderly with reduced health. Given the importance of high response rate in surveys, a cost of 1 working hour per additional response is likely to be worth while. TRIAL REGISTRATION: Registration with ISRCTN initiated on 05/21/2013 and finalised on 06/30/2014 with http://www.isrctn.com/ISRCTN31304930. Following the prospective submission in May 2013, there were no subsequent changes to the protocol. The recruitment started on 01/06/13, after initiation of public registration.