The relationship between tip size and evaluations of the service was assessed in a meta-analysis of 7 published and 6 unpublished studies involving 2,547 dining parties at 20 different restaurants. Consistent with theories about equity motivation and the economic functions of tipping, there was a positive and statistically significant relationship between tip size and service evaluations. However, that relationship was much smaller than is generally supposed. The confounding effects of customer mood and patronage frequency as well as the reverse-causality effects of server favoritism toward big tippers were all examined and shown to be insufficient explanations for the correlation between tipping and service evaluations. These findings suggest that tippers are concerned about equitable economic relationships with servers, but that equity effects may be too weak for tip size to serve as a valid measure of server performance or for tipping to serve as an effective incentive for delivering good service.
Lynn, M., & McCall, M. (2000). Gratitude and gratuity: A meta-analysis of research on the service-tipping relationship [Electronic version]. Retrieved [insert date], from Cornell University, School of Hospitality Administration site: http://scholarship.sha.cornell.edu/articles/152