Payment in challenge studies from an economics perspective

[...]this study suggests that limits on payments are not justified if one takes subjects’ own objectives as the relevant normative standard. [...]a part of the ethics literature attaches significantly more weight to concerns of undue inducement than the general population. [...]it appears to us that there is sufficient public support for preparing for challenge trials, with paid participants, without a need for excessive ethical concern that payments might inadvertently become too generous to trial participants.