system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do psychology researchers obtain informed consent without tipping their subjects off on the subject of the study?

I know that subjects of research studies must give informed consent before they are allowed to participate. I also know that informing subjects of psychological experiments of the study's true purpose can influence the results. How are these two concerns reconciled?
gpt
You have to tell them what will happen to them during the study.  You don't have to tell them why you are doing it or what conclusions you will draw, except in the vaguest of terms.  "You will answer a series of timed questionnaires while being observed by our researchers, to increase our knowledge about how people make decisions".  Maybe they don't care about your answers to the quizzes, only your facial expressions while you take them.