Evidence, Strategy and Results Department, The Joint United Nations Programme on HIV/AIDS, Geneva, Switzerland.
PLoS One. 2012;7(1):e31184. doi: 10.1371/journal.pone.0031184. Epub 2012 Jan 27.
Men who have sex with men (MSM) are one of the groups most at risk for HIV infection in Japan. However, size estimates of MSM populations have not been conducted with sufficient frequency and rigor because of the difficulty, high cost and stigma associated with reaching such populations. This study examined an innovative and simple method for estimating the size of the MSM population in Japan. We combined an internet survey with the network scale-up method, a social network method for estimating the size of hard-to-reach populations, for the first time in Japan.
An internet survey was conducted among 1,500 internet users who registered with a nationwide internet-research agency. The survey participants were asked how many members of particular groups with known population sizes (firepersons, police officers, and military personnel) they knew as acquaintances. The participants were also asked to identify the number of their acquaintances whom they understood to be MSM. Using these survey results with the network scale-up method, the personal network size and MSM population size were estimated. The personal network size was estimated to be 363.5 regardless of the sex of the acquaintances and 174.0 for only male acquaintances. The estimated MSM prevalence among the total male population in Japan was 0.0402% without adjustment, and 2.87% after adjusting for the transmission error of MSM.
The estimated personal network size and MSM prevalence seen in this study were comparable to those from previous survey results based on the direct-estimation method. Estimating population sizes through combining an internet survey with the network scale-up method appeared to be an effective method from the perspectives of rapidity, simplicity, and low cost as compared with more-conventional methods.
男男性行为者（MSM）是日本 HIV 感染风险最高的群体之一。然而，由于难以接触到这些人群、成本高以及耻辱感等问题，对 MSM 人群进行规模估计的工作并未频繁且严谨地开展。本研究检验了一种在日本评估 MSM 人群规模的创新且简单的方法。我们首次在日本将网络扩展法（一种用于评估难以接触人群规模的社交网络方法）与互联网调查相结合。
我们对一家全国性互联网研究机构的 1500 名注册互联网用户进行了一项互联网调查。调查参与者被问及他们认识多少名特定群体（消防员、警察和军人）的成员，这些群体的人数是已知的。参与者还被要求指出他们认识的多少名熟人是男男性行为者。使用这些调查结果和网络扩展法，估计了个人网络规模和 MSM 人群规模。无论熟人的性别如何，个人网络规模估计为 363.5，仅为男性熟人时为 174.0。未经调整时，日本男性总人口中 MSM 的估计流行率为 0.0402%，调整 MSM 传播误差后为 2.87%。
本研究中估计的个人网络规模和 MSM 流行率与基于直接估计法的先前调查结果相当。与更传统的方法相比，通过将互联网调查与网络扩展法相结合来估计人群规模，从快速、简单和低成本的角度来看，这种方法似乎是一种有效的方法。
