RESUMO
The objective of this study was to assess the trends of sampling locations and methods of studying hard-to-reach populations conducted in Japan. We accessed a Japanese medical database on 30 September 2005 to review 5 study types of hard-to-reach populations conducted in Japan: men who have sex with men, homeless, sex workers, undocumented migrants, and injecting drug users. We then categorized their sampling locations and methods. We found 298 articles on hard-to-reach populations published from 1983 to September 2005. Of the 285 studies sampled, approximately 92% were facility-based studies and the rest were community-based. This tendency was consistent in each subgroup; the majority of the studies were conducted among patients in medical facilities. Our study shows the majority of studies on hard-to-reach populations in Japan adopted a convenience sampling method and were facility-based. We suggest the utilization of comparatively valid techniques, such as time-location or respondent driven sampling to more clearly understand these populations.