Applications Of Capture Recapture Method In Estimating The Size Of Activity Homosexual Men Population In Hangzhou

BackgroundThere are a large number of homosexuals in China, and they are at high risk for human immunodeficiency virus (HIV) infection and transmission. Currently the epidemiological studies on acquired immune deficiency syndrome (AIDS) mainly focus on the HIV infection rate of different high-risk populations, behavioral risk factors, and molecular epidemiology. However, few researches have been conducted to estimate the base number of the homosexual men who are the high-risk population for HIV. There has been no research result on the exact incidence of homosexual men in China. This study aims to estimate the number of active homosexual men in Hangzhou City by establishing a capture-recapture model and compared with the results by point observation method, so as to compare the estimation methods for a special population, accumulate experience for future large-scale investigations on such populations.MethodsThe data were collected from the epidemiological investigations on homosexual men in Hangzhou City by Professor Xu yi (from Zhejiang University School of Medicine) during the period of 2000 to 2004. The numbers of homosexual men were obtained by counting the numbers of homosexuals attending two homosexual parties: one was held in a bar and the other was held outside bar in December 2003 and January 2004. The capture-recapture log-linear models were established, and analyzed by GENMOD in SAS 9.0. The number of homosexual men was estimated by point observation method in October 2000. The number of active homosexual men in Hangzhou City was estimated.Results:1) From 2000 to 2004, the number of active homosexual men by the three investigations was 1250 in October 2000,1324 in December 2003, and 1411 in January 2004.2) The estimated numbers by the capture-recapture log-linear models were 1917 (1748-2203) and 2210 (1992-2549) in December 2003 and January 2004, respectively.3) The estimated number was 2013 (1925,2101) by point observation method in October 2000.4) The results of two methods are quite consistent,so the capture-recapture log-linear models is practicable. The estimated number of active homosexual men in Hangzhou City is 2064.Conclusions:1) The capture-recapture log-linear model is an easy, practical and accurate method to estimate the number of active homosexual men in Hangzhou City.2) The estimated number of active homosexual men in Hangzhou City is 2064 (95% confidence interval:1870-2376).