How many men are there in Vancouver who have sex with other men?

It's a tricky question for numerous reasons. While U.S. sex researcher Alfred Kinsey's estimate that one in ten men is homosexual has been traditionally cited though has since been discredited, B.C. researchers have come up with a different number.

In an effort to help effectively healthcare providers plan services to address the HIV epidemic, researchers from the University of British Columbia, the B.C. Centre for Excellence in HIV/AIDS, and several other Canadian and U.S. organizations and universities conducted an attempt to try to specify numbers of what includes a potentially "hidden population".

In the study, which was published in the Journal of Urban Health in June, the researchers point out that census data for sexual orientation has not been routinely collected in Canada or worldwide. Further complicating matters, definitions of sexual orientation can vary between being behaviour- versus identity-based. Stigma can also prevent disclosure or participation in studies. For instance, a 2014 web-based survey involving 8,382 Canadian MSM found that 30 percent stated they would be unwilling to disclose their sexual identity in a government survey.

These factors, in addition to other challenges, can prevent an accurate collection of data from men who have sex with men (MSM) populations, which includes men who may not identify as LGBT.

For this study, researchers drew upon four data sources:

• the national cross-sectional Canadian Community Health Survey (CCHS), conducted by Statistics Canada;

• a bio-behavioural MSM survey, provided by the Momentum Health Study;

• HIV testing services data from three local sexually transmitted infection (STI) clinics;

• and Facebook data.

Based on responses to the Momentum survey question about what participants perceived to be the size of the local MSM population, the MSM population was estimated to be 10,000 men (or 1.1 percent of adult men in Metro Vancouver), the lowest estimate in the study.

Facebook data, based on 18,200 user profiles listing being "interested in men" or "interested in men and women", produced an estimate of 23,760 men (2.5 percent of Metro Vancouver men). The report points out that as these were based upon public disclosures of interest in men, estimates were therefore based only on those who chose to disclose. (There is also potential for the Facebook "interested in" question to be open to interpretation, such as seeking platonic friendships rather than sexual attraction.)

An estimate based on the general population survey of the Vancouver urban core by the CCHS resulted in a number of 30,605 men (3.3 percent).

The average estimate for the numbers collected from the local STI testing clinics was 41,777 men (4.5 percent).

Based upon these four estimated numbers, the average estimate turned out to be 27,183 men, or 2.9 percent of the Metro Vancouver adult male population.

The report acknowledges that many of the methods of collecting data were susceptible to potential underreporting, misclassification, or lack of disclosure. The researchers add that "one or all of the components of sexuality may change over the life course".

Accordingly, there may be men who may not be included in reported numbers, such as men who have had sexual experiences with other men but do not disclose or deny their experiences, or those who experience but, to date, have not yet acted upon their sexual or emotional attraction to other men.