Guess the menstrual cycle of the stripper by how much you tip her!

The results of Ovulatory cycle effects on tip earnings by lap dancers: economic evidence for human estrus? (Miller, G., Tybur J. M., Jordan, B.D.; 2007) are a great mix of - and, as the authors say - have clear implications for human evolution, sexuality, and economic. In this study, the effects of ovulatory cycles on tip earnings of professional female lap dancers working in gentlemen's clubs were examined.
During estrus (period of maximum sexual receptivity in females of many animal species), lap dancers earned almost twice as much money in tips than during menstruation (and 50% more than during the luteal phase). However, for those lap dancers who were using hormonal contraceptive pills an increase in tip earnings during the same time frame did not occur. Fascinatingly enough, women who were using contraceptive pills on average earned less tips than those who weren't, throughout whole the cycle (approximately two thirds less per cycle)!

Some previous studies showed that women become more attractive during estrus (body scent, facial attractiveness, waist-to-hip ration, verbal fluency, ...), as well as that they tend to dress more attractively, and that their male partners become more protective of them. This (small, with only 18 participating women) study presents the first real-world economic evidence of such an effect.

This beautiful paper also contains a collection of references for interviews with gentlemen's clubs' managers, as well as a detailed introduction to a working day of a lap dancer, for academics who "may be unfamiliar with the (...) subculture."