Study on using the multiplier method in estimating the size of men who have sex with men population in Shanghai

Objective To estimate the size of men who have sex with men(MSM)in Shanghai. Methods Multiplier method was used in the study and two popular Shanghai-based MSM websites were selected as targeted institutions.The number of MSM(r)who visited website during a given period was investigated by a web-based questionnaire.Meanwhile,a survey was conducted among MSM living in Shanghai to obtain the proportion of MSM who had visited the websites during the given period,the reciprocal number of this proportion was the multiplier(m),therefore,population size can be estimated by r multiplied by m.Results The MSM population was estimated as 398 433 when website A was selected as target institution and 370 755 was estimated when website B was selected.The estimated population of MSM accounted for 7.1% and 6.6% of male population aged 15 to 49 years old in Shanghai,respectively. Conclusion It was feasible to use multiplier method which selecting MSM website as target institution to estimate the size of MSM population,however,the representativeness of this study sample should be considered seriously.