In-Store Slack: Pitt Researchers Find That Consumers Often Plan For Unplanned Purchases

Straying from the grocery list can yield some surprises in your shopping cart, but not necessarily in your wallet, according to University of Pittsburgh researchers and a coresearcher from Baylor University who have coauthored a new study.

The researchers found that shoppers often expect to buy a certain number of unplanned items, and most have a fairly accurate estimate as to how much they will spend on them. The study’s coauthors used the term “in-store slack” to describe the room shoppers leave in their budget for unplanned purchases.

The study, “Planning to Make Unplanned Purchases? The Role of In-Store Slack in Budget Deviation,” will be published in the August issue of the Journal of Consumer Research. It was written by Jeffrey Inman, associate dean for research and faculty, Albert Wesley Frey Professor of Marketing, and professor of business administration in Pitt’s Joseph M. Katz Graduate School of Business; Karen M. Stilley, postdoctoral fellow in the Katz School; and Kirk L. Wakefield, a professor and chair in the marketing department at Baylor University’s Hankamer School of Business.

The researchers conducted a field study at several grocery stores in Texas. Shoppers were asked what they intended to purchase, how much they expected to spend on the planned items, and how much they intended to spend total. After shopping, participants provided their receipts and answered questions about themselves and their purchases. More than 75 percent of the participants included room in their mental budgets for unplanned purchases.

“Shoppers in the study indicated that they employ this strategy both because they anticipate ‘forgotten needs’ as well as because they realize that they will encounter ‘unplanned wants’—with some respondents even explicitly indicating that they expected to make impulse purchases,” the authors wrote. The shoppers were remarkably accurate when predicting how much they would spend. The average budget deviation (actual spending minus planned spending) was only 47 cents.

The impact of in-store slack on household budget deviation depended on how many aisles the shopper visited and the shoppers’ level of impulsiveness.

For retailers, this research suggests that consumers who shop only specific aisles are not spending all of the money that they are mentally prepared to spend on the current trip, according to the authors. The fact that most consumers do not exceed their mental budgets despite making unplanned purchases suggests that different product categories function as substitutes (i.e., should I spend my in-store slack on ice cream or Parmesan cheese?). Therefore, the researchers believe future research should further examine whether in-store stimuli may simply serve to redirect what items consumers purchase rather than generate incremental spending.