Ratios of one variable over another are frequently used in social psychological research in order to control for a hear relationship between the numerator and the denominator. However, the use of ratio variables can introduce spuriousness into data analyses. This article provides a description and explanation of the problem of spuriousness in ratio correlations and it illustrates this problem with research on restaurant tipping.
Lynn, M., & Bond, C. F. (1992). Conceptual meaning and spuriousness in ratio correlations: The case of restaurant tipping [Electronic version]. Retrieved [insert date], from Cornell University, School of Hospitality Administration site: http://scholarship.sha.cornell.edu/articles/42