My co-author in Houston put a joint working paper online about experiments in China. The abstract:
We compare the characteristics and regression coefficients between the participants in a field experiment in China and the survey population from which they were recruited. The experimental participants were more educated, younger, more likely to be male, more risk-loving and work fewer hours than the more general population. The estimates of their regression coefficients in the standard analyses of wages, happiness and entrepreneurship differed significantly from non-participants, indicating that inferences drawn from experimental samples may not hold for more representative groups of the population.