Cost analysis
When assessing the cost of each intervention, a full economic analysis was not undertaken. We assessed the gross cost impact per diary in a simple cost analysis. When considering this there were different factors to take into account. The first and most important was the cost of the vouchers themselves, £20 per voucher dispensed. The indirect costs must also be taken into consideration, administration time and the cost of postage.In the non-conditional arm, it was the recruiter, most commonly a GP, who was giving out and completing the required forms and receipts for each voucher given. Five minutes would be allowed for an administrative task such as this when considering NHS service support cost reimbursements. At this time, a GP time was reimbursed at £80 per hour according to the NHS research reimbursement figures.In the conditional arm, the amount of time required for the administration was a similar 5 min, but this task would be completed by an administrator whose time was charged at £21 per hour. In addition to this, there was the postal cost of sending the voucher to the participants for which the cost of a second class letter was £0.56.To assess the impact of the direct and indirect costs, we took into account the number of times each item or activity was required, according to the number of vouchers given and so calculated a total cost per arm and then a total cost per questionnaire returned. No formal analysis of the results was carried out and the cost per diary returned for each group was calculated.