“Half of the people who sign up for Obamacare (ACA) get a flurry of medical care, then drop out before a year is over,” Stanford economist John Cochrane writes in summary on a new working paper. “They can always sign up again if they need to. People who stay on insurance tend to be those who have ongoing chronic and expensive conditions that need continual care. The implications for the viability of such insurance are not good.”

The paper draws on very detailed banking data in 2014 and 2015 (which seems about as anonymized as NSA metadata collection from mobile phones), so behavior is likely unaffected by policy changes promised or threatened by Donald Trump as candidate or president.

Cochrane concludes, “Of course, we could transition to personal, portable, guaranteed-renewable, time-consistent insurance instead…Oh, stop dreaming.”