A consortium of retailers and consumer suppliers are working with Nielsen Co., famous for its nonsensical television ratings system, to launch a large-scale study of consumer behavior in stores. The program is called PRISM, which stands for “Pioneering Research for an In-Store Metric,” and it uses infrared sensors and manual counting, as well as genetic clones of our loved ones, to monitor not just what we buy but how we go about buying it. “About 70% of final purchase decision are made at the shelf,” says a Procter & Gamble rep. “The store has always been important – we just didn’t know enough about it.”