Neilsen's PRISM media measurement in jeopardy

The leading media measurement service in the U.S., Neilsen Co. has suffered a major blow as the largest retailer in the U.S., Walmart, declined to go ahead with a comprehensive in-store measurement service called PRISM.According to a story in MediaDaily News, the complete system -- in which Walmart took part at the beta stage -- was scheduled to be rolled out this year and there were suggestions