Scoop pen sub-study-a ‘trial within a trial’ of enclosing a pen in questionnaire mailings to increase response rate

Results Of the 3,789 participants sent a 60-month questionnaire in the pen group, 3,500 (92.4%) returned it compared with 3,462/3,793 (91.3%) in the control group (OR 1.16, 95% CI 0.98 to 1.37, p=0.08). There was evidence of a reduction of the number of reminders required (p=0.02) and the time taken to respond (p=0.01) in the pen group. Some difference was found in the completeness of the primary outcome (p=0.05). The pooled OR of response rates...