**2. Methods**

Our sample includes adult Californians surveyed before and after the California Supreme Court decision (CSCD) in 2008. We obtained data from CHIS for years 2005–2015. Initially fielded biennially, CHIS became a continuous survey in 2011. Administered in five languages, it employs a multi-stage probability design that selects subjects by random-digit dial within geographic strata. Respondents in this analysis include adults ages 18–70 who self-identified as heterosexual, lesbian/gay female, or gay male. CHIS did not ask sexual-identity questions of participants older than 70 [24]. We excluded respondents who said they were bisexual, celibate, non-sexual, or provided no response because the CHIS survey did not ask the sex/gender of a respondent's spouse [19] and thus lacked the ability to safely intuit the sex/gender of each respondent's spouse. CHIS obtained human subject approval for participant recruitment and data collection through the University of California, Los Angeles (UCLA). The National Institutes of Health's Office of Human Subjects Research Protection determined our study to be exempt from review as it involved the study of existing data recorded such that subjects cannot be identified.

#### **2.1 Dependent variable**

#### *2.1.1 Psychological distress*

CHIS has fielded the Kessler 6-item (K6) scale to assess nonspecific psychological distress since 2005 [25]. The K6 measures symptoms during the past 30 days: felt nervous, hopeless, restless or fidgety, worthless, depressed, and felt that everything *Psychological Health Influences of Legal-Marriage and -Partnerships on Same-Sex Couples DOI: http://dx.doi.org/10.5772/intechopen.90249*

was an effort—using Likert scales from 0 representing none of the time, to 4 representing all the time. The K6 scale is summed with scores of 0 representing lowest, and 24 representing the highest psychological distress level. Dichotomized moderate mental distress is defined as the sum of K6 scores at or above 5, the optimal lower threshold indicative of moderate mental distress [13]. The K6 continuous measure and the dichotomized moderate mental distress scores have demonstrated reliability and validity in population datasets, including CHIS [26, 27]. We used the dichotomous measure given our small subsample of married and partnered same-sex couples.
