WASHINGTON (MarketWatch) -- U.S. private-sector firms shed 693,000 jobs in December, far worse than expected, according to the ADP employment index released Wednesday. Employment in the services sector fell by 473,000, while employment in the goods-producing sectors fell by 220,000. The methodology for the ADP index has been revised with the aim of making it a better fit with the government figures to be released on Friday. Economists currently expect nonfarm payrolls to have fallen by 500,000 in December.