- Mark Dolliver

A new research paper challenges the popular notion that unplanned purchases are the norm when people shop at the supermarket. According to a Knowledge@Wharton summary of the findings, such thinking has encouraged retailers to "to devote growing resources to in-store promotion -- for example, featuring certain products at the ends of aisles and in checkout lines to encourage impulse buying."

While not dismissing the importance of in-store marketing, the paper's authors -- Wharton marketing professor David R. Bell and a couple of overseas academics -- argue that some kinds of shoppers are more prone than others to making unplanned purchases and, as such, more susceptible to the influence of such marketing efforts.

The research is based on close observation of shopper behavior in the Netherlands, though Bell says the findings "can be applied generally to American retailers as well." (One caveat, though: Many Dutch shoppers walk to the grocery store, and walkers were less likely to make unplanned purchases than those who drive to the store, as Americans typically do.) "The most basic information the research revealed is that no unplanned buying was done on slightly more than 60 percent of all shopping trips," says the Knowledge@Wharton bulletin. "On the rest of the trips, the shoppers made an average of three unplanned purchases -- far fewer than previous research indicated."

The research also noted significant variations in the incidence of unplanned buying among different demographic cohorts. It found young, unmarried, upper-income adult households doing 45 percent more such buying than the overall average.

Conversely, "Households led by an older person and those that have larger families do 31 percent to 65 percent less spontaneous purchasing." Self-described "fast and efficient" shoppers are, predictably, far to the below-average end of the spectrum, making 82 percent fewer unplanned buys than the overall average. And what if the shopping trip itself is unplanned? Unplanned purchases go up 23 percent in such cases. But if the excursion is "a major or weekly trip," unplanned purchasing is 13 percent lower than the norm.