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Prevention Science published an RCT of High School FLASH, a sex ed program, reporting that it reduces homophobic & transphobic beliefs. Quick take: Not a credible result (only suggestive), as this was a post-hoc analysis that can easily yield chance findings.


  • Per the study: “High School FLASH is a comprehensive sexual health education curriculum … for classroom settings, with the specific behavior change goals of preventing unintended pregnancy, preventing STDs, and preventing the perpetration of sexual violence.”

Study Design & Prior Findings:

  • The study randomly assigned 20 schools in the U.S. South and Midwest, with a student sample of 1,597 9th and 10th graders,  to (i) a treatment group that received FLASH vs (ii) a control group that received a knowledge-based sexual health curriculum.

  • A prior study report found no discernable impact of FLASH vs control on the study’s 2 pre-specified primary outcomes: the full-sample rates of vaginal sex, & vaginal sex without birth control, measured at 3 and 12 months after program completion.

New Findings:

  • The newly-published article reports statistically significant positive impacts on students' homophobic & transphobic beliefs at 3 & 12 months post-program.

  • Importantly, however, this was not a pre-specified primary or secondary outcome of the study, per the study registration.

    In other words, it’s a post-hoc outcome. Analyses of such outcomes are only suggestive under established scientific standards (FDA, IES), as they can easily yield chance (i.e., false) results.

  • The reason is that each statistical significance test has about a 1/20 chance of producing a false result, for a program whose true effect is zero. So a study like this that examines numerous outcomes & subgroups can easily turn up false findings.


  • Claiming effectiveness based on post-hoc findings is a bit like placing a bet on a horse after watching the race. The findings are not without value but I think only suggestive.

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