It's one of the most impressive statistics about the new health care law. The Obama administration says more than 8.9 million people have been, quote "determined eligible" for Medicaid from Oct. 1 through the end of January.
But a new study Monday from Avalere Health estimates the actual number of new sign-ups could be much lower, between 2.4 million and 3.5 million.
The administration's statistic also includes many people renewing existing coverage.
Medicaid is a safety-net health program for low-income people. About half the states have accepted an expansion in the health law.
Avalere's estimate includes people eligible for the expanded program, as well as some who were already eligible but had not previously enrolled. Enrollment picked up in January.
Explore further: Lower Medicaid signups seen in new study