Warren Buffett’s decision to leave the newspaper business is just the latest setback for an industry that has been suffering for years. An index of six U.S. newspaper stocks dropped 61% from the beginning of 2015 through Wednesday, according to data compiled by Bloomberg. The decline contrasted with a 50% gain in the Class B shares of Berkshire Hathaway Inc., Buffett’s company. Lee Enterprises Inc., which agreed Wednesday to purchase Berkshire’s papers for $140 million, is in the index. A.H. Belo Corp., Gannett Co., McClatchy Inc., E.W. Scripps Co. and Tribune Publishing Co. are also included.