Kevin Yung Recruiting participants

A nice considered discussion of the problems (and solutions) for recruiting research subjects - thanks. I'm interested in your point about whether paying subjects is ethical. In our ethics approval process, we try to encourage researchers to give something back (like your writing tutorial) but discourage payments. However, a large chunk of the discipline of psychology is based on research into paid students at US universities. As well as the problem of basing a discipline on a small subset of the human population, I always wonder why psychology (a discipline which is normally at the forefront of research rigour) seems to have no issues with paying subjects. Do you think paying subjects potentially biases research, and do you think it's ethical?