Sexual orientation has also been studied as a risk factor for PPD. In a 2007 study conducted by Ross and colleagues, lesbian and bisexual mothers were tested for PPD and then compared with a heterosexual sample group. It was found that lesbian and bisexual biological mothers had significantly higher Edinburgh Postnatal Depression Scale scores than did the heterosexual women in the sample. These higher rates of PPD in lesbian/bisexual mothers may reflect less social support, particularly from their families of origin and additional stress due to homophobic discrimination in society.