The Ideal Free Distribution (IFD) theory (Fretwell & Lucas, 1970) was proposed to describe how animals living in the wild distribute themselves between two different resource sites (patches). According to the IFD theory, the ratio of animals in the two resource sites (n1 / n2) is equal to the ratio of resources obtained in those sites (r1 / r2). Because of its similarity to Herrnstein's (1961) matching law, the IFD has been described as "group matching." The present studies systematically replicated and extended previous tests of the IFD theory in humans (e.g., Sokolowski et al. 1999). A group 12 undergraduate students was asked to choose blue or red cards to earn points. Like foraging animals that share food available at a resource site, our groups shared the total points allocated to the blue and red cards. In the first experiment, each choice trial was divided into two parts. First, participants chose a colored card when prompted to do so. Then, participants had a chance to switch the color chosen. The second experiment was slightly different in that participants were not given the opportunity to switch the card originally selected. This procedure reduced the probability that participants would verbally evaluate their anticipated earnings. A different number of points was allocated to each color and these points changed across five conditions. The results of the present studies replicated previous findings and showed that the IFD theory accurately predicted the number of participants at each resource site.

Fretwell, S. D., & Lucas, H. L. Jr. (1970). On territorial behavior and other factors influencing habitat distribution in birds. Acta Biotheoretica, 19, 16-36.

Sokolowski, M. B. C., Tonneau, F., & Baque, E. F. (1999). The ideal free distribution in humans: An experimental test.Psychonomic Bulletin and Review, 6, 157-161.