Shares of insurance broker Willis Group Holdings Plc plunged 10.7 percent in New York trading yesterday, after fourth quarter profits fell by more than half from last year.Revenue declined and the third-largest broker, behind Aon and Marsh, missed analysts’ earnings estimates.Willis fell $4.15 to close on $34.52 in New York yesterday.Fourth-quarter net income dropped to $40 million from $98 million a year earlier, the London-based company said in a statement late on Tuesday. Operating profit was 46 cents a share, missing by two cents the average estimate of 15 analysts surveyed by Bloomberg.Organic revenue, which excludes the effect of currency fluctuations and acquisitions, slipped one percent. The drop was fuelled by declines in the UK and Ireland retail business and the North American operation that provides coverage on homes when borrowers fall behind on their payments.The slump “demonstrates the challenges that our business endured in the final months of the year and shows where we must improve in 2012”, chief executive officer Joe Plumeri said in the statement. “We’re obviously not satisfied.”