A recent study published in JAMA Pediatrics suggests that the legalization of same-sex marriage is associated with a reduction in the proportion of high school students who reported making a suicide attempt. This study indicates that governmental policies regarding non-normative sexuality may have an influence on mental health outcomes for adolescents.

The study used data from the state-level Youth Risk Behavior Surveillance System, which tracks dangerous and risky behaviors exhibited by teenagers. Its authors used data from forty-seven states, including thirty-two states that implemented same-sex marriage policies between 2004-2015. They looked at suicide behaviors in the full population of high school students and then did a secondary analysis using the subset of students who self-identified as belonging to a sexual minority (gay, lesbian, bisexual, or unsure about their sexual identity).

One limitation of using this type of data is that it depends on self-reporting of suicide attempts, which is tricky because suicide attempts are typically under-reported. This approach also means that the researchers did not include any information about teens who died from their suicide attempts; it only captures teens who attempted suicide but survived. This methodological limitation may seem like a big one, but the proportion of suicide attempts that result in teen deaths is very small, so suicide attempts are a reasonable proxy for overall teen mental health.

The researchers used a “differences-in-differences” approach to analyze this data. This analysis allows researchers to use observational data about an intervention to approximate the effects that would be seen in a randomized controlled trial for the same intervention. In other words, this approach treats observational data as though that data came from a “natural experiment,” one with an intervention group (states that implemented same-sex marriage) and a control group (states that did not). This method looks at the difference in pre-intervention suicide attempts data and post-intervention suicide attempts data for these two groups, hence the name “difference-in-difference.”

The researchers quantified the difference in number of attempted suicides in states that passed laws legalizing same-sex marriage and states that did not pass those laws. Finally, they compared the difference in suicide attempts for the same two groups of states before same-sex-marriage legalization and after.

The comparison of these differences is important to ensure that changes in rates of suicide attempts are not associated with large-scale cultural changes. By tracking individual states, the researchers could identify local attitudes regarding sexual orientation. Still, the authors couldn’t control for individual-level differences, such as economic status or religious affiliation. These demographic characteristics could play an important role in determining the likelihood of a suicide attempt. Future studies that look more closely at individuals and their personal social context are needed.

Using differences-in-difference, the researchers saw that legalization of same-sex marriage was associated with a statistically significant decline in suicide attempts for all teens—a seven percent relative reduction in suicide attempts for adolescents of all sexual orientations. The association between same-sex marriage legalization and reduction in suicide attempts was also significant for teens who identified as sexual minorities. For this subgroup, there was a 14-percent relative reduction in suicide attempts after the passage of same-sex marriage laws.

Looking at the longitudinal suicide-attempt data, the authors saw that these reductions in suicide attempts persisted for up to two years after legalization of same-sex marriage. The persistence of this drop suggests that any backlash regarding same-sex marriage didn’t make things any harder on teens.

JAMA Pediatrics, 2017. DOI: 10.1001/jamapediatrics.2016.4529 (About DOIs)