People who end up in the emergency room complaining of chest pains a few weeks before their 40th birthday are very similar to people who end up in the emergency room with chest pains a few weeks after their 40th birthday. But on a chart, the former are 39 years old and the latter are 40.

The point of these studies isn’t to titter or sigh at the peculiarities of human reasoning but to use these natural experiments to estimate the effect of medical procedures. If the only reason that near-18 and 18-year-olds are prescribed opioids differently is the semantics of “child” and “adult,” then we can use the discontinuity in prescriptions as a natural experiment—it’s as if prescribing around the age of 18 were randomly assigned. The authors find, for example, that compared to the just-under-18s, the just-over-18s were 12.6% more likely to later be diagnosed for an opioid-related adverse event such as an overdose. The greater rate of overdose is valuable information—but imagine the difficulty of trying to convince an Institutional Review Board that it would be ethical to randomly prescribe opioids to young people.

source: MR