According to fourth quarter estimates released this week by the NPD Group, Apple’s iTunes continues its stronghold with a 63 percent unit share of the U.S. market for digital music downloads. Amazon.com’s MP3 store held second place at 22 percent. Notably, the NPD “Annual Music Study 2012” indicates that eight out of 10 consumers downloaded digital albums or tracks during the fourth quarter from iTunes.

“The estimates are based on units, rather than revenue,” explains The Hollywood Reporter. “Because iTunes discounts far less often than rival retailers, its dollar share of the $2.9 billion U.S. download market is likely to be greater than its unit share, though NPD did not provide dollar share figures.”

The study further suggests that the “number of Americans buying digital music downloads has remained stable over the last three years at roughly 44 million people, despite the spread of inexpensive or free streaming alternatives such as Pandora, Spotify and YouTube.”

“There’s a belief that consumers don’t need to buy music because of streaming options,” said Russ Crupnick, NPD’s senior VP of industry analysis. “In fact, streamers are much more likely than the average consumer to buy music downloads.”

More than one third of those surveyed indicated that owning music remains important to them, and many noted that they made purchases after discovering new music on streaming services.

According to the RIAA, digital download sales grew 8.9 percent last year in the U.S.