The federal government's general awareness-building ads increased overall ACA exchange plan enrollment, and eliminating the ads entirely might cut enrollment by up to 6.7% in some markets, the economists found.

The TV ads appeared to be about 40% as effective at increasing enrollment as exchange deadline reminder letters that the Internal Revenue Service mailed to taxpayers who appeared to be uninsured.

The economists are more skeptical about the power of insurers' own ads.

Overall, "it is not very clear that private advertising is effective in increasing enrollment at the market level or at the insurer level," the economists write.

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When the economists analyzed the data one way, they found that an insurer's own ads could help it take some business away from competitors without expanding the market.

When the economists analyzed the impact of health insurers' TV advertising another way, the ad impact was "very small and not statistically different from zero."

"We do not rule out the possibility that private advertising is not effective at all," the economists write.

Naoki Aizawa, an economist at the University of Wisconsin-Madison, and You Suk Kim, an economist at the Federal Reserve Board, have published the paper in the American Economic Journal: Economic Policy.

Study details: The economists looked at plan enrollment data for 2014 through 2018 from HealthCare.gov, which provides ACA exchange services in more than 30 states, along with plan enrollment data for the same period from the ACA exchange programs in California and New York.

The analysis also included TV ad spending data for the period from Kantar Media.

What it means: The economists who wrote the paper said they hope to apply their analytical approach to determining the value of different types of advertising for other insurance products and other types of services, such as electricity and mortgage loans.

For brokers who are still in the retail insurance market, the study demonstrates the power of institutional, awareness-building advertising.

For benefits brokers and employers, the study could have a bearing on enrollment in voluntary group plans and efforts to sell individual products at the worksite through payroll-deduction payment arrangements.

If Aizawa and Kim are correct, educational materials from sources that employees think of as neutral parties might work better than materials that highlight the features of specific insurers' or distributors' benefits products.