A U.S. manufacturing activity index rose to an 11-month high in December, Markit economics said Thursday. December's purchasing managers index rose from 54.7 in November -- at the time a 10-month high -- to 55, Markit said. The index indicates growth with numbers above 50. In a separate report, the Institute of Supply Management pegged the country's manufacturing PMI at 57, which indicates faster growth than Markit's estimate. On the other hand, ISM's data shows growth slowing, as their November index put the PMI at 57.3. Markit said their new orders index slid from 56.2 to 56.1. The new export orders index held steady at 51.4. Markit's employment index rose from 52.3 to 54. The backlog of work index indicated slightly higher growth at 52.8, up from November's 52. Input and output price indexes both rose, climbing to 59 and 55.6, respectively. "The upturn in the PMI in December rounds off one of the strongest quarters for manufacturing since the economy pulled out of recession," said Markit Chief Economist Chris Williamson said in a statement. "The goods producing sector is therefore on course to provide a firm boost to the economy in the fourth quarter, which we expect to see growing at an annualized pace of at least 3 percent," he said. "This tells us that business spending is picking up on the back of rising confidence, which adds to the sense that the recovery is being more self-sustaining," he said. ISM said 13 of 18 manufacturing sub-sectors showed growth in the month, including, in order of fastest growth to slowest, furniture production, plastics and rubber products, textile mills; apparel; computer and electronic; paper products; transportation equipment; primary metals; fabricated metal; wood products; printing; food, beverage and tobacco production and miscellaneous manufacturing. Non-metallic mineral products; machinery; chemical products; and electrical equipment and appliances showed declines in the month.