IDC lowered its forecast for tablet sales for all of 2014 today by 6.3%, pointing to the cannibalization of small tablets by larger smartphones known as "phablets" -- those with displays of over 5.5-inches.
Also, there's evidence that consumers are keeping their existing tablets much longer than originally predicted, IDC said.
IDC's original tablet forecast for the full year expected sales totalling 260.9 million tablets, including 2-in-1 tablet-laptops; IDC has now reduced that number to 245.4 million tablets.
Tablet shipments will still increase compared to last year by 12.1%, IDC said, but that's far below the 51.8% growth in 2013 over the prior year.
Phablets made up 10.5% of all smartphone shipments in the first quarter of 2014, or about 30.1 million shipped. That's more than double the 4.3% share of smartphone sales phablets had in the first quarter of 2013.
The emergence of phablets has caused customers to "second-guess tablet purchases as the larger screens on these phones are adequate for tasks once reserved for tablets," Tom Mainelli, an IDC analyst, said in a statement.
He noted that consumers are keeping their current tablets, especially more expensive models like recent 9.7-in. iPads and the iPad Air, for "far longer than originally anticipated."
Mainelli added via email: "A $500 iPad tends to have a longer lifetime than an $80 Android tablet."
IDC analyst Jitesh Ubrani said via email that while some consumers were expected to replace an older tablet after perhaps two years, "in some cases, we're seeing [tablets kept for] three to 3.5 years."
If a family does buy a second tablet, the original one is kept in use by another member of the family, Mainelli said. "We've found that a huge percentage of people who buy a new tablet go on to hand down their existing tablet to someone else in their household so that a three-year-old device doesn't get recycled out of the installed base," he said. "Instead, it starts a new life with a new owner and all of this is impacting shipment growth."
Because of the negative impact of phablets on smaller tablets in the 7-in. to 8-in. range, IDC predicted greater buyer interest in larger tablets with displays of more than 8 inches, even some with 11-in. displays or larger, like the new 12-in. Surface Pro 3, a 2-in-1 device.
Vendors will welcome sales of larger tablets because their average selling prices can be 50% higher than sub-8-in. tablets, said Ubrani.
Microsoft also will benefit from this expected interest in larger tablets because of the Surface Pro 3 and a general interest in Windows-based devices with their ability to run work-based productivity software.
IDC has said that Windows-based tablets, now forecast to take 5% of the tablet market for all of 2014, should more than double to 10.4% in 2018. Tablets running iOS are forecast to top 30% in 2014 and drop to nearly 28% in 2018. Android tablets, forecast to reach 64.4% of the tablet market in 2014, should decline to about 62% in 2018, IDC said.
While tablets in the 7-in. to 8-in. range made up 55% of all tablets shipped in 2013, that percentage is expected to fall to 44.5% in 2018, IDC said. Tablets from 8 in. to 11-in. made up 44% of the market in 2013, and will climb to nearly 49% in 2018. The 11-in. and larger tablets were less than 1% of the market in 2013 and will grow to 6.6% of the market by 2018.
Matt Hamblen covers mobile and wireless, smartphones and other handhelds, and wireless networking for Computerworld. Follow Matt on Twitter at @matthamblen or subscribe to Matt's RSS feed. His email address is email@example.com.