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Table 2 Outcomes

From: Evaluation of the effects of an offer of a monetary incentive on the rate of questionnaire return during follow-up of a clinical trial: a randomised study within a trial

Outcome First mailout (n = 503) Reminder (n = 515) Effect measure (95 % CI)
n % n %
Primary outcome      
Questionnaire returned
 Postal
 Online
373
 306
 67
(74.2)
 (82.0)
 (18.0)
370
 285
 85
(71.8)
 (77.0)
 (23.0)
RRa 1.03 (0.96 to 1.11)
Secondary outcomes      
Questionnaire returned without chasing by study team
 Postal
 Online
259
 207
 52
(51.5)
 (79.9)
 (20.1)
217
 161
 56
(42.1)
 (74.2)
 (25.8)
RRa 1.22 (1.07 to 1.39)
Total cost of vouchers, £ 3790   1530   MD 4.56 (4.02 to 5.11)
Cost of vouchers per participant, £ – mean {SD} 7.53 {4.31} 2.97 {4.57}  
  1. aAdjusted for centre
  2. SD standard deviation, RR risk ratio, MD mean difference
  3. Values are numbers (percentages) unless stated otherwise