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SAN FRANCISCO — The outlook for the struggling personal computer industry is worse than was previously believed, according to market research firm IDC, which on Thursday cut its 2013 forecast for global PC shipments for at least the second time.

Worldwide shipments of PCs are likely to fall 9.7 percent this year as consumers continue to favor mobile gadgets, IDC said in a report.

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That is much worse than IDC's prediction in March that PC shipments would fall 1.3 percent this year and below its forecast in May of an 7.8 percent annual drop.

"The days where one can assume tablet disruptions are purely a First World problem are over," said Jay Chou, IDC senior research analyst, Worldwide Quarterly PC Trackers, in a statement.

The growing popularity of tablets and smartphones has thrown the PC industry into its longest downturn on record and IDC said it expects PC shipments to keep falling at least through next year.

China and other developing economies had been a source of healthy demand for PCs in the face of falling sales in the United States and Europe. But shipments in those countries are now set to decline in 2013 even more than in wealthy regions, IDC said.

Also on Thursday, IDC nudged lower its forecast for 2013 tablets, pointing to the growing use of smartphones with large screens as well as an expected demand for new categories of wearable devices such as smart watches.

Global tablet shipments are now expected to grow 57.7 percent from last year to 227.4 million units, instead of 229.3 million units, IDC said.