<qa>  What is the only way to encourage screening participation?A wider use of incentives in public health interventions is a more recent phenomenon and has attracted controversy and concerns about whether they are effective and cost effective or not. This study will provide evidence to policy makers about the role of different incentive schemes in encouraging health promoting behaviours. We do not suggest that providing incentives is the only answer to encouraging screening participation, but if we demonstrate good evidence that they are effective and cost effective, their targeted application may be indicated. Equally demonstration that incentives of this type are not effective may prevent unnecessary financial loss from the NHS if wider rollout of such programmes is considered. 