what determines how much money you get of the "up to" money offered for participating in a research study?

I see ads in the newspaper everyday asking for healthy males, age 20-40, no history of diabetis, non-smokers, problems sleeping, etc; who might be eligible to participate in a research study at some medical center and receive compensation of *up to * x amount of dollars.The keyword, of course, being "up to." If chosen to participate in a research study, what determines whether you get the full amount or just a dollar?
Answers:
Sometimes there are different groups in a research study, such as the "control" group and the "intervention" group. The control group stays as normal as possible, while the intervention group gets the experimental whatever experience. Often it's random which group you are in, and sometimes even you or the experimenter don't know which. You shouldn't think of it as "pay", so much as reimbursement for your voluntary charitable service to the quest for knowledge. The more you are inconvenienced (or even endangered) the more you are reimbursed, depending on what kind of funding the research is getting.
Whatever you do, ask lots of questions, read the CONSENT DOCUMENT carefully, and don't sign it if you don't trust the experimenters.

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depends if live thru the experiment

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