Hilary L. Surratt, PhD, Associate Scientist for the Center for Drug and Alcohol Studies at the University of Delaware, et. al., in the July 2005 Journal of Psychology & Human Sexuality study titled "The Connections of Mental Health Problems, Violent Life Experiences, and the Social Milieu of the 'Stroll' with the HIV Risk Behaviors of Female Street Sex Workers," wrote:

“[I]n contrast to popular thinking, female sex workers are an extremely heterogeneous population. They are situated in a myriad of social and environmental contexts…

Past and current studies suggest that there are many different types of female sex workers, including ‘call girls’ and escorts working in the upper echelons of the sex industry, ‘in-house’ sex workers working in parlors or brothels, ‘street-walkers’ who sell sex for money through sidewalk solicitations, part-timers who supplement their incomes with sex-for-pay, and drug-involved street-based sex workers, the majority of whom shift between sex-for-money and sex-for-drug exchanges as circumstances require.”

July 2005