Impact of legalization of same-sex marriage on the new HIV infection rate in 172 countries around the world based on difference-in-differences (DID) method

Abstract

Abstract Background: Acquired immunodeficiency syndrome is a major global health challenge, which is exceedingly harmful to human health. This study aimed to explore the impact of legalization of same-sex marriage on the new HIV infection rate in countries around the world. Methods: The study is conducted on 172 countries whose observed data were collected from 1996 to 2019 in an open-source website. To evaluate the effect of legalization of same-sex marriage, difference of differences (DID) method was applied. The treatment effect was reported in static DID model, and the time-varied treatment effect and its 95% CI were reported in dynamic DID model. Results: In the static DID model, we found that compared with countries without legalization of homosexuality, countries with legalization of same-sex marriage had an increase of 0.129‰ (95%CI: [-0.234,0.491]) in the new HIV infection rate, but the result was not statistically significant. In the dynamic DID model from 1996 to 2010, we found that the fifth year after the implementation of same-sex marriage legalization policy significantly increased the new HIV infection rate by 0.7‰. But in other years the effect are not significant after the policy enforcement. The implementation of same-sex marriage legalization policy has no significant effect on the new HIV infection rate during 1996-2019, but increase the rate in early year from 1996-2010, although the latter result seems incredible because of the unbalance of the sample in 1996-2010. Conclusion: Based on current study, the policy on legalization of same-sex marriage has no significant effect on new HIV infection rate. It seems that legalizing same-sex marriage do not intervene HIV transmission, but more evidence is needed and the mechanism remains to be studied.