The effects of psilocybin are highly variable and depend on the mindset and environment in which the user has the experience, factors commonly referred to as set and setting. In the early 1960s, Timothy Leary and colleagues at Harvard University investigated the role of set and setting on the effects of psilocybin. They administered the drug to 175 volunteers from various backgrounds in an environment intended to be similar to a comfortable living room. Ninety-eight of the subjects were given questionnaires to assess their experiences and the contribution of background and situational factors. Individuals who had experience with psilocybin prior to the study reported more pleasant experiences than those for whom the drug was novel. Group size, dosage, preparation, and expectancy were important determinants of the drug response. In general, those placed in groups of more than eight individuals felt that the groups were less supportive, and their experiences were less pleasant. Conversely, smaller groups (fewer than six individuals) were seen as more supportive. Participants also reported having more positive reactions to the drug in those groups. Leary and colleagues proposed that psilocybin heightens suggestibility, making an individual more receptive to interpersonal interactions and environmental stimuli. These findings were affirmed in a later review by Jos ten Berge (1999), who concluded that dosage, set, and setting were fundamental factors in determining the outcome of experiments that tested the effects of psychedelic drugs on artists' creativity.