the male inmates tended to form hierarchical social groups based on perceived characteristics and abilities. Life in prison involves many hardships and deprivations, and prisoners often alleviate these through interpersonal relationships. There is a continuing scholarly debate over the nature of prisoner subculture: while some sociologists argue that society and culture within prisons are unique, created primarily or exclusively by the circumstances of imprisonment, others hold that these societies are determined by wider cultural influences. In the latter view, the presence of inmate culture can be caused by discomforts of imprisonment, but the form and structure of inmate social groups is definitively determined by cultural norms and expectations from culture external to prison life. One major piece of evidence used to support this argument is the structural differences of male and female inmate society. There are also debates over the nature and cause of prisoner social groups. One theory is that social groups are formed to reduce the discomforts of incarceration, and are therefore directly caused by the nature of imprisonment, while others believe that personal experience and the structure of each particular institution have more impact on inmate social structure. Additionally, some scholars believe that social groups form differently in male and female populations, while others hold that groups are fundamentally the same in men's and women's prisons. Differences between male and female inmate culture Charles Tittle conducted a study of inmate social groups in a Federal hospital serving a large groups of prisoners suffering from narcotics addiction in 1969, in which he compared the experiences of female inmates to those of the males. He found that women were significantly more likely to identify as having a close group of friends; 70% of female respondents said that they had one to five good friends, as compared to 49% of males. Tittle conjectures that these findings indicate that under comparable circumstances, women are more likely to form 'primary group affiliations' while men are more likely to integrate into the overall social organization. He states that male inmate social groups tend to be more symbiotic and to place higher value on individualism than female inmate groups were observed to do. Gangs as social organizers in prison More recent studies have focused on trends which are caused by the rapid increase in prison population since the 1970s, such as the prominence of prison gangs. In his literature review and analysis of evidence