ByJohn S. McClenahen Initial claims for unemployment insurance plunged unexpectedly during the week ending Oct. 5. The number of claims fell 40,000 to 384,000, reports the U.S. Labor Department's Employment & Training Administration. The four-week running average for jobless claims also fell. It's now at 412,250, down some 12,500 from its previous mark. There's considerable reason, however, to believe that the dramatic decrease in the number of claims for the week ending Oct. 5 does not signal a major job market change for the better. Much of the reported 40,000 decrease apparently relates to statistical difficulties -- namely making the proper seasonal adjustments to raw data at the beginning of the calendar quarter. "It could be several weeks before claims give an accurate reading of job market trends," says Maury Harris, chief U.S. economist at UBS Warburg LLC, New York. Meanwhile, other Labor Department data show that both prices of goods and materials coming into the U.S. and the prices of those being exported increased in September. Led by higher prices for petroleum, the Import Price Index rose 0.7% in September, its sixth monthly gain. The petroleum price index, which has increased in eight of the last nine months, has risen 61.1% since December 2001. Led by higher prices for agricultural products, the U.S. Export Price Index rose 0.2% in September, the same as its August gain. However, the price index for capital goods exports, which account for nearly half of all U.S. exports, fell 0.2% in September.