To keep insurers from weeding out ill people when offering coverage, the ACA prohibited them from denying coverage due to preexisting conditions, or to charge premiums so high that the expense would serve to winnow out sick people. But of course that meant that insurers could end up with a sizeable population of insureds sicker, and thus more expensive, than they expected.

The permanent risk-adjustment program, the report says, is aimed at keeping insurers in the individual and small group insurance markets from selling only to healthy low-risk individuals rather than achieving a mix of healthy and ill plan members.

The program works by collecting payments from plans with members who are healthier than the average, then distributing that money to plans with a high concentration of sick, high-cost members. It works based on a patient's risk score, which is determined by demographic and health condition data.

The reinsurance program ran for three years and terminated in 2016; what it did was to protect insurers from high-dollar claims. Insurers pay into the reinsurance pool, and those funds are then paid out to health plans that had members with extremely high medical claims.

The study finds that most of the revenue flowing through the risk-adjustment program went from insurers with low paid claims to insurers with high paid claims. Additionally, in the reinsurance program, insurers that had higher paid claims received higher revenue than insurers with lower paid claims, with the 25 percent of insurers with the highest claims getting more than twice as much as insurers with the lowest claims received in reinsurance revenue. And together, the two programs increased most insurers' revenue relative to their claims.

In 2014 and 2015, claims were higher than premium revenue by $90–$397 per enrollee per month for the 30 percent of insurers with the highest claims. But once the two programs' contributions to revenue were factored in, the result was the opposite, the study finds, with premium revenue exceeding insurance claims by $0–$49.

In addition, researchers also find that smaller insurers — some of which had complained that the risk-adjustment program was unfairly favorable to bigger insurers with more extensive claims experience — actually ended up benefiting the most from both programs.