Risk adjustment is one of three methods built into the 2010 health-care law to help insulate insurance companies from the ACA requirement that they accept all customers for the first time — healthy and sick — without charging more to those who need substantial care.

The other two methods were temporary, but risk adjustment is permanent. Federal health officials are required each year to calculate which insurers with relatively low-cost consumers must chip in to a fund, and which ones with more expensive customers are owed money. This idea of pooling risk has had significant practical effects: encouraging insurers to participate in the insurance marketplaces the ACA created for Americans who cannot get affordable health benefits through a job.