NEW YORK (AP) - Apple continues to dominate in tablet computers, although its market share is shrinking because of growing competition from Samsung and others, research firm IDC said Thursday. Apple Inc. shipped 22.9 million iPads worldwide in the October-December quarter, during which it released a smaller version and updated its full-size models. That's growth of 48 percent from the same period a year earlier. But IDC said Apple's market share fell to 44 percent, from 52 percent. Samsung Electronics Co., maker of the Galaxy line of devices, saw shipments more than triple to 7.9 million. Its market share expanded to 15 percent, from 7 percent. AsusTek Computer Inc., maker of the Transformer line and Google's Nexus 7, also saw shipments and market share increase. Amazon.com Inc.'s share fell despite shipping more Kindle Fires during the quarter. Barnes & Noble, maker of the Nook tablets, saw both market share and shipments fall. IDC said Microsoft Corp. didn't make the top 5 despite the high-profile release of the Surface tablet running a version of its new Windows 8 system. Overall, there were more than 52 million tablets shipped during the quarter, an increase of 75 percent. Here are the top five manufacturers of tablets in the fourth quarter, as released by IDC: Apple Inc., 22.9 million shipped worldwide, 43.6 percent share (15.5 million, 51.7 percent a year earlier) Samsung Electronics Co., 7.9 million, 15.1 percent (2.2 million, 7.3 percent a year earlier). Amazon.com Inc., 6.0 million, 11.5 percent (4.7 million, 15.9 percent a year earlier) AsusTek Computer Inc., 3.1 million, 5.8 percent (600,000, 2.0 percent a year earlier) Barnes & Noble, 1.0 million, 1.9 percent (1.4 million, 4.6 percent a year earlier) Others, including Microsoft, 11.6 million, 22.1 percent (5.5 million, 18.5 percent a year earlier)