Walmart has announced that it will not be a part of PRISM when Nielsen's experimental in-store marketing measurement tool goes live next year. Walmart was one of the original backers of the initiative, so their departure is a blow, but it is not really all that surprising, nor does it fatally wound PRISM.
Combined with Walmart's absence from syndicated data, this may seem to indicate a chronic inability to commit, but a more likely explanation is simply that Walmart feels that their competitors may gain more from having Walmart data in the mix than Walmart gains from being in the consortium -- the same reason they withhold their POS from the syndicators. Having been part of the pilot, Walmart now knows enough about how the new tool works to do the same thing on their own and make it part of RetailLink.
It makes perfect sense, though it is no doubt a disappointment to Nielsen, and will further complicate the lives of marketers who were looking forward to the new tool.
I was initially dismissive of PRISM, because I felt sales data was a better measure of the effectiveness of in-store marketing, but I came around as I appreciated better that PRISM's purpose is different (to measure brand-building) and should be seen as supplemental and complementary to sales measures, rather than as an attempt to supplant those measures.
While Walmart's defection means that PRISM measurements will be less comprehensive, that does not mean they will be without value. We will continue to look forward to PRISM's rollout and hope that it fulfills marketers' hopes.