NEW YORK (AP) -- Shares of McDonald's Corp. fell more than 4 percent Friday after the fast-food giant reported a slowdown in some overseas markets and missed analysts' expectations on a key revenue measure.The company said revenue at stores open at least 13 months declined 0.3 percent in August in the region of Asia/Pacific, the Middle East and Africa. That marked the first monthly decline in that area since November 2009. The company didn't give many specifics on how individual countries fared but said a slowdown in Japan offset strength in China and Australia.Companywide, revenue at stores open at least 13 months rose 3.5 percent, the company's 100th consecutive month of growth by that metric. However, that missed analysts' expectations for a 4.9 percent rise.The figure climbed 3.9 percent in the U.S. and 2.7 percent in Europe, McDonald's largest market.The figures are a snapshot of money spent on food at both company-owned and franchised restaurants. They do not reflect McDonald's corporate revenue, which consists of revenue at company-owned stores plus fees and rents paid by franchisees. They are a key measure of a restaurant chain's operating performance, because they exclude the impact of recently opened or closed stores.Shares fell $3.58, or 4.04 percent, to close at $85.03 Friday.However, any slowdown in the emerging markets is particularly troubling because McDonald's, like many companies, is turning to fast-growing countries in those regions to fuel growth as U.S. customers get tapped out. Asia, the Middle East and Africa made up 22 percent of McDonald's revenue in the second quarter, up from 13 percent five years ago. The U.S. now accounts for 31 percent of McDonald's revenue, down from 34 percent five years ago.Analysts at Stifel Nicolaus and Sterne Agee lowered their estimates for McDonald's third-quarter and full-year earnings, citing the revenue numbers and the company's tax predictions.McDonald's said it expects its effective tax rate to be 33 to 34 percent in the third quarter, because of a noncash charge related to some foreign operations. It said it continues to expect its effective tax rate for the full year to be 31 percent to 32 percent, though that would still be higher than 2010's 29.3 percent.Some of the pressures on McDonald's are a result of its own success. A 3.5 percent increase would be the envy of many fast-food chains. McDonald's has consistently outperformed its peers throughout the recession and its aftermath, enticing loyal customers with low prices and luring new ones by trying to remake itself as a hip, healthy place to eat, with fancy coffee drinks, wireless access and remodeled restaurants.Analysts said Friday that the fast-food giant is poised to continue growing even as other fast-food chains struggle, thanks to its recognizable brand, low prices and adaptability to changing tastes.McDonald's said it tentatively plans to release results for the third quarter, which covers July through September, on Oct. 21.AP Business Writer Michelle Chapman in New York contributed to this story.