Economists recognize that preferences can differ across individuals. We examine the strengths and weaknesses of lab and field experiments to detect differences in preferences that are associated with standard, observable characteristics of the individual. We consider preferences over risk and time, two fundamental concepts of economics. Our results provide striking evidence that there are good reasons to conduct field experiments. The lab fails to detect preference heterogeneity that is present in the field, obviously due to the demographic homogeneity of the lab. There are also differences in treatment effects measured in the lab and the field that can be traced to interactions between treatment and demographic effects. These can only be detected and controlled for properly in the field data. Thus one cannot simply claim, without additional empirical argument or assumption, that treatment effects estimated in the lab are reliable.

Length: 34 pages

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Morten Igel Lau

CEBR

Copenhagen Business School

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>E: mol@cebr.dk