An Iowa State University economist who tracks retail activity at the so-called “Big Box” stores like Wal-Mart, Target and K-Mart says those chains don’t always offer the lowest price on every item. Iowa State University economist Ken Stone says consumers tend to believe the slogans like “everyday low prices” but don’t really know the “going price” of very many things. Stone says research indicates consumers know the “going price” of about one percent of the items they purchase, things they buy with frequency like milk or dog food. Stone says, for example, Wal-Mart tracks competitors prices on what they call their “850 list” — the 850 most commonly-purchased items in their store. Wal-Mart managers have the authority to immediately lower prices on any of those items found to be selling cheaper in a competing store in the area. Stone says when you least expect it, Wal-Mart has much higher prices on infrequently purchased items. Stone says Wal-Mart’s prices on high-wattage light bulbs are much higher than local grocery stores in Iowa. Stone recently discovered a north central Iowa grocery store selling G-E soft white 150 watt light bulbs for $1.33. Wal-Mart’s standard price for the pack is $1.98.