The issue of whether, and how much, to compensate subjects for research participation is something IRBs and researchers struggle with. Is a particular compensation scheme affordable given available funding? Will the proposed compensation be so high as to unduly influence the target population’s decision to join a study? Or is it so low that it doesn’t adequately compensate people for their time and inconvenience?
One researcher found that data about compensation is sorely lacking, and argues that making compensation information more available would provide some context for researchers trying to set compensation levels, and IRBs considering them. See a summary of his findings in a recent publication in IRB Advisor (scroll down to find the article). The PRIM&R blog also published an item on this issue, which has links to additional resources.