There are a lot of unpleasant numbers for Republicans in the Congressional Budget Office’s assessment of their health care bill. But congressional leadership found one to cheer: The report says that the bill will eventually cut the average insurance premiums for people who buy their own insurance by 10 percent.

House Speaker Paul Ryan pressed that point in a series of appearances Monday night, suggesting that the budget office had found that the House bill would increase choice and competition and lead to lower prices. The Senate majority leader, Mitch McConnell, issued a statement saying, “The Congressional Budget Office agrees that the American Health Care Act will ultimately lower premiums and increase access to care.”

But the way the bill achieves those lower average premiums has little to do with increased choice and competition. It depends, rather, on penalizing older patients and rewarding younger ones. According to the C.B.O. report, the bill would make health insurance so unaffordable for many older Americans that they would simply leave the market and join the ranks of the uninsured.

The remaining pool of people would be comparatively younger and healthier and, thus, less expensive to cover. Other changes would help make health insurance skimpier — cheaper, but with deductibles that are higher than those criticized by Republicans under Obamacare.