Mark Lepper

Mark Lepper

Mark Lepper is a professor of psychology at Stanford University. He is the first author of the 1973 study that established the overjustification effect, and the co-author, with Sheena Iyengar as first author, of the 2000 jam study that founded research on choice overload.

Who they are

Lepper studies motivation, particularly intrinsic motivation and the effects of reward. Two findings this site draws on bear his name.

This page records only what the papers and their published records state. Biography beyond the cited work is not given here.

Key papers

The overjustification study (1973), with Greene and Nisbett. Journal of Personality and Social Psychology. Preschoolers who were promised a reward for drawing later drew less in free time than children who were not. The study had 51 participants.

When choice is demotivating (2000), Iyengar and Lepper. Journal of Personality and Social Psychology. At a supermarket tasting table, 60 per cent of passers-by stopped at a display of 24 jams against 40 per cent at a display of 6, but of those who stopped, nearly 30 per cent bought after seeing 6 jams against 3 per cent after seeing 24.

Key ideas

The overjustification finding has held up well. Deci, Koestner and Ryan's 1999 meta-analysis of 128 experiments supports it, with the conditions attached: tangible, expected rewards on a task people already enjoy.

The jam study has a more contested record. Direct repeats did not find the effect, a 2010 meta-analysis found the average close to zero, and a 2015 meta-analysis found that choice overload appears under specific conditions, such as hard comparisons and uncertain preferences.

Sources

  1. Lepper, M. R., Greene, D., & Nisbett, R. E. (1973). Journal of Personality and Social Psychology, 28(1), 129-137.
  2. Iyengar, S. S., & Lepper, M. R. (2000). When choice is demotivating: can one desire too much of a good thing? Journal of Personality and Social Psychology, 79(6), 995-1006. doi:10.1037/0022-3514.79.6.995