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The Trump administration on Friday narrowed an Obama-era mandate on contraception coverage, allowing more employers and insurers to exempt themselves from providing such coverage under religious or moral grounds.

Part of the administration's justification for the new policy is that such coverage could increase "risky sexual behavior" among teenagers. From the proposed rule published today in the Federal Register:

"Imposing a coverage Mandate ... could, among some populations, affect risky sexual behavior in a negative way. For example, it may not be a narrowly tailored way to advance the Government interests identified here to mandate contraceptive access to teenagers and young adults who are not already sexually active and at significant risk of unintended pregnancy."

This argument, however, is contradicted by what has actually happened since the mandate was put in place.

The federal government has been collecting solid data on risky teen behaviors since the 1990s, thanks to the national Youth Risk Behavior Surveillance Survey (YRBSS), sent to a nationally representative sample of thousands of American high-schoolers every two years.

Data from that survey shows that in the years since the Obamacare contraception mandate went into force in 2012, risky teen sexual behavior has declined — in some cases sharply.

The proportion of high school students who ever had sex dropped from 47.4 percent in 2011 to 41.2 percent in 2015. The share who were currently sexually active fell from 33.7 to 30.1 percent. Similar declines were apparent among the rate of teens having sex before age 13, and the share of teens having four or more sexual partners.

One indicator moving in the opposite direction is the share of sexually active teens who didn't use a condom the last time they had sex. Although this has been on the rise over the past several years, it also was increasing at the same rate in the years immediately prior to the contraception mandate.

These numbers don't show causation — they don't indicate that the contraception mandate caused the observed decreases. But they are very hard to square with the notion, which the Trump administration asserts, that the coverage mandate could "affect risky sexual behavior in a negative way."

One more key datapoint, which comes from the Centers for Disease Control and Prevention's National Vital Statistics System, is the teen birth rate. The CDC just released those numbers for 2016. They show that teen births have plummeted by more than 50 percent in recent years, dropping from 41.5 births per 1,000 teen girls age 15 to 19 in 2007 to 20.3 births per 1,000 this year.

Experts generally agree that contraception availability is a key factor in that decline.