“…Potential predictor variables for our outcome measure included a variety of factors found to be significantly associated with UAI or with lack of HIV testing in previous studies, or else considered to be biologically plausible causal factors for either of these behaviors. We considered: sociodemographic characteristics (age [ 11 ], income [ 11 , 12 ], education [ 13 ], size of city of residence, residence in a state in the former Western or Eastern part of Germany, immigration background, sexual orientation); relationship characteristics (type and length of relationship [ 2 , 14 , 15 ], knowledge of partner’s HIV status [ 15 ], frequency of UAI with steady partner [ 13 ]); psychological and social variables (symptoms or diagnosis of depression or anxiety [ 15 ], any professional help for psychological symptoms, internalized homophobia [ 15 , 16 ], experience of violence due to sexual orientation, “outness” [ 12 ], social support [ 11 ], HIV-related stigma [ 17 ]); use of establishments (such as bars, clubs, or saunas) that cater toward gay men [ 13 ]; proportion of sexual partners met on the Internet [ 18 ]; knowledge and attitudes toward HIV [ 19 ], condom use [ 14 , 15 ], and antiretroviral therapy (ART) [ 12 , 20 ]; satisfaction with sex life in general; and substance use [ 12 , 13 , 15 ]. All variables were self-reported.…”