One subtheme that the Naked Anthropologist concentrates on particularly is the unreliability of statistics and their misuse to justify different policies, not only for sex workers but for stigmatized population groups in general. In one recent post, for instance, she mentions how counts of sex workers in 19th century European cities tended towards the high end, using questionable statistics to imply that prostitution was relatively common and that prostitutes couldn't be permanently excluded (after they were reformed, of course).
Mr Tait, a writer on prostitution in Edinburgh, whose estimates I receive with every respect, but at the same time with considerable reserve, informs us that in that city they number about 800, or nearly 1 to every 80 of the adult male population. In London he considers they are as 1 to 60; in Paris, as 1 to 15; and in New York, as 1 to 15.
The manner of these calculations is as follows: One-half of the population of each place is supposed to be males, of whom one-third are thrown aside as too young or too old for exercise of the generative functions. The remainder is then divided by the alleged number of public women in each community-namely, in Edinburgh, 800; in London, 8000; in Paris, 18,000; and in New York, 10,000.
It appears that the above estimate for London is not far short of the mark, the number of recognised women being about 8600; but the number of males, of twenty years of age and upwards, being close upon 700,000 (632,545 in 1851), we should arrive at the proportion, for London of one prostitute overt to every 81 (not every 60) adult males.* It will be observed, also, that in attributing 8000 public women to London and 18,000 to Paris, this writer has not allowed for the enormous clandestinity of our own capital, while he has more than quadrupled the French official returns, I presume, on that account.
In her most recent post, Agustín criticizes the statistical methods used to estimate illegal immigrants in the United States as problematic.
Methods for estimating undocumented migrants do exist (undocumented migrants being the framework in which trafficking victims should be located). In the following example, the Pew Hispanic Center (in Washington DC) publishes its new figure (11.1 million in March 2009), asserting that their method of calculation, the residual method, is reliable and widely accepted because based on ‘official government data’. They explain that:
Under this methodology, a demographic estimate of the legal foreign-born population—naturalized citizens, legal permanent residents, temporary legal residents and refugees—is subtracted from the total foreign-born population. The remainder, or residual, is the source of population estimates and characteristics of unauthorized immigrants. These Pew Hispanic Center estimates use data mainly from the Current Population Survey (CPS), a monthly survey of about 55,000 households conducted jointly by the U.S. Bureau of Labor Statistics and the Census Bureau. It is best known as the source for monthly unemployment statistics. Each March, the CPS sample size and questionnaire are expanded to produce additional data on the foreign-born population and other topics. The Pew Hispanic Center estimates make adjustments to the government data to compensate for undercounting of some groups, and therefore its population totals differ somewhat from the ones the government uses. Estimates for any given year are based on a March reference date.
The Pew says they use the Current Population Survey. That is a census exercise, in which a form is sent to households to fill out. Undocumented migrants have abundant reasons for not filling in census forms correctly (and there are no penalties for filling them in incorrectly). So undercounting is likely. The Pew Center know that and make an adjustment, but the range of adjustment methods is also very wide
Percentages ranging from 10 to 40 are suggested.
Anyway. There's plenty at the Naked Anthropologist to interest the average reader at Demography Matters. Go, read.