Miller et al. (2007) tested the ‘hidden-estrus’ theory, which suggests that unlike other female mammals, humans do not experience an ‘estrus’ phase during which they are more sexually receptive, proceptive, selective and attractive. If this theory is wrong then human heterosexual men should find women most attractive during the fertile phase of their menstrual cycle compared to the pre-fertile (menstrual) and post-fertile (luteal) phase. Miller used the tips obtained by dancers (id) at a lap dancing club as a proxy for their sexual attractiveness and also recorded the phase of the dancer’s menstrual cycle during a given shift (cyclephase), and whether they were using hormonal contraceptives (contraceptive). Dancers provided data from between 9 and 29 of their shifts. Fit a multilevel model using these data (miller_2007.sav) to see whether tips can be predicted from cyclephase, contraceptive and their interaction, allowing the overall level of tips to vary across dancers. Is the ‘hidden-estrus’ hypothesis supported?