Halpern 2004.

Methods	Randomised controlled trial
Data	Setting: secondary care, USA. 126 participants who had mild to moderate hypertension and who met standard entry criteria (unclear what these are) for phase II and III trials at the clinic), attending clinic on selected interview days. Exclusion criteria were unable/unwilling to give oral informed consent and any exclusion criteria for the current phase III trials at the clinic (it was unclear what these were)
Comparisons	Intervention A: the variables altered were information regarding the percentage of previous patients who experienced adverse effects from the study drug (10%, 20% and 30%) and the payment participants would receive (USD 100, USD 1000, and USD 2000). Intervention B: the variables altered were the percentage of patients who would be assigned to placebo (10%, 30% and 50%) and the payment level
Outcomes	Willingness to participate in a hypothetical trial (patients were told the trial was real but then told trial was not after decision)
Notes
Risk of bias
Item	Authors' judgement	Description
Random Sequence generation ok?	No	Allocated by alternate day of week
Allocation concealment?	No	See above
Blinding of participants and personnel ok?	No	Participants blind but not investigator, who could, in principle, influence their responses because data collection was via interview
Blinding of outcome assessment ok?	No	Outcome not objective and not clear what influence unblinded investigator might have had on this.
Incomplete outcome data handled ok?	Yes	Adequate
Free of selective reporting?	Yes	Willingness to take part outcome presented, which is all the review needs
Was the study free of other bias?	Unclear	Hypothetical study, though participants were initially told it was real; yet each was told about 9 scenarios "after patients had indicated their [willingness to participate] in all 9 trials …" Not clear if participant considered these real or not.
Overall bias?	Yes	High risk of bias