Caitlin Myers and myself have been studying the effect of House Bill 2 in Texas, which closed half the state's abortion clinics, on marriage rates using "continuous difference-in-differences" estimation for 14 episodes straight.

But behind every good diff-in-diff estimate lurks a parallel trends assumption, and so we asked Hannah to look into one confounder -- oil! fracking! energy! Perhaps things related to technologies that enhanced the extraction of oil from the ground, like fracking technology, could have alone shifted marriage rates by bringing men into communities but only for work, temporary residence, not permanence.

We talk about a literature where men in transit can alone reshape the marriage markets, which if those events happened disproportionately in our treatment counties, but also our control counties, then parallel trends mechanically *might* be violated. Because remember -- parallel trends is a) about things differentially impacting the treatment and control units on *outcome trends* and b) therefore can impact the treatment group *or* the control group. Hannah comes back with research she did for us on it.

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