Estimating the size of hard-to-reach populations: a novel method using HIV testing data compared to other methods

Area of Science:

• Epidemiology
• Public Health
• Biostatistics

Background:

• Estimating the population size of hard-to-reach groups, such as injecting drug users (IDUs) and men who have sex with men (MSM), is crucial for effective public health interventions.
• Traditional survey methods often struggle to accurately capture these populations due to accessibility and reporting challenges.

Purpose of the Study:

• To estimate the population size of injecting drug users and men who have sex with men in Canada's three largest cities: Toronto, Montreal, and Vancouver.
• To develop and validate a novel indirect method for population size estimation by comparing it with existing methodologies.

Main Methods:

• A novel indirect method was developed, combining HIV serodiagnostic information with HIV testing behavior data.
• Population size was estimated by dividing the number of individuals in HIV databases by the proportion tested for HIV within a year.
• This indirect method was compared with population surveys, capture-recapture, modified Delphi technique, and a method based on never-married men (for MSM).

Main Results:

• The indirect method yielded estimates comparable to other methods, though potentially slight overestimates for IDUs.
• Point estimates for IDUs in Toronto and Vancouver were 17,700 and 17,500, respectively; for MSM, they were 39,100 and 15,900.
• Other methods produced a wide range of estimates across cities, highlighting the challenges in precise population sizing for these groups.

Conclusions:

• The novel indirect method provides reliable population size estimates for hard-to-reach groups like IDUs and MSM.
• These estimates are valuable for planning, implementing, and evaluating prevention and care services.
• Combining estimates from multiple methods can enhance confidence and improve the accuracy of population size estimations.