Non RANDom panel attrition update

Here I enthuse about a criticism by John Nyman of a RAND study on the effect of copayments on demand for health care and health outcomes.

Still following in the footsteps of a kid half my age, I note that Ezra Klein notes that RAND has responded to the criticism with this pdf.

The RAND study was a genuine experiment in which participants were randomly assigned to complete coverage or one of 6 different plans with copayments. RAND concluded that demand for health care was reduced by copayments but found significant worsening of health outcomes only for some poor participants.

The original Nyman critic noted that participants with less generous programs were much more likely to switch back to their original insurance plans (as they were allowed to do). If sicker people did so, this could bias the result.

I have just begun to read the RAND reply but I have already learned that RAND attempted to follow the health outcomes of people who switched out of the experimental plans and has data on health outcomes of 77% of them compared to 85% of people who stuck with the plans. Thus the attrition problem is much smaller than I thought after reading Nyman's abstract (I would have had to pay his actual article).

Just thought I should say that.