Several US newspapers are about to offer advertisers deals based on results. If a series of ads does not result in at least a 10% increase in sales volume, the last ad in the series will be free.The initiative has been launched by the Newspaper National Network, which is owned by 25 major newspaper publishers and the Newspaper Association of America.Deals will be offered first to national marketeers that sell packaged goods like health and beauty aids, food, beverages and household products. It follows tests during the last two years involving eight packaged-goods brands sold by giant companies such as Campbell Soup, General Mills, PepsiCo and Procter & Gamble. All eight gained sales, the newspaper network said, with increases that ranged from 7% to 25%. The average was 16%.