David Kanouse, PhD, Senior Behavioral Scientists at the RAND Corporation, et al., in the Feb. 1999 Journal of Sex Research article "Drawing a Probability Sample of Female Street Prostitutes in Los Angeles County," wrote:
"[L]ittle of what is known about the size of this population... has been derived from careful scientific study. Most studies of prostitutes rely on samples of convenience, typically recruiting in jails, STD clinics, and methadone maintenance programs. A few studies also include outreach recruitment of respondents in areas known for street prostitution...
The usual way to minimize sampling bias is through the use of probability sampling techniques. However, the nature of commercial sex work makes that approach especially difficult. Because prostitution is an illicit activity, registries or rosters of prostitutes are not available... persons in the general population who are willing to admit to such activity is inefficient and unlikely to yield satisfactory coverage of the target population."
Ronald Weitzer, PhD, Professor of Sociology at George Washington University, in the July 2005 Violence Against Women article "Flawed Theory and Method in Studies of Prostitution," wrote:
"In no area of the social sciences has ideology contaminated knowledge more pervasively than in writings on the sex industry. Too often in this area, the canons of scientific inquiry are suspended and research deliberately skewed to serve a particular political agenda."
Wendy McElroy, Research Fellow at the Independent Institute, in the Nov. 12, 1999 Spintech Magazine article "Prostitution: Reconsidering Research," wrote:
"The public discussion on prostitution has become an ideological brawl in which both sides bend research to promote political agendas and to slander opponents. Those on the sidelines who feel bewildered by a conflicting flood of arguments and evidence should find solace in the fact that some researchers are just as bewildered."
Élaine Audet, Associate Editor of Sisyphe.org, wrote the Mar. 1, 2005 article "The Need For a Public Debate on Prostitution and Its Social Consequences" on its website that stated:
"It is, of course, impossible to talk of women in prostitution as a whole, because the situation of the individuals differs substantially, depending on whether they are escorts or nude dancers, work on the streets or in massage parlours, are independent or have to give a substantial share of their earnings to a pimp."
Melissa Farley, PhD, Founding Director of the Prostitution Research and Education, wrote an essay for the Oct. 16-17, 2003 conference Demand Dynamics: The Forces of Demand in International Sex Trafficking in Chicago titled "The Demand for Prostitution" that said:
"Johns are secretive, and it's not easy to interview or research them. It is almost impossible to estimate how many men in the world have bought women for sex. Even where prostitution is legal, much of johns' behaviors are hidden from public view."