For some kinds of experiments, Mechanical Turk is helping to alleviate the problem: http://pps.sagepub.com/content/6/1/3.short http://pps.sagepub.com/content/6/

For some kinds of experiments, Mechanical Turk is helping to alleviate the problem: http://pps.sagepub.com/content/6/1/3.short http://pps.sagepub.com/content/6/1/3.short