Researchers say 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 use the term "in-store slack" to describe the room shoppers leave in their budget for unplanned purchases.
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, associate professor and chair of the marketing department at Baylor University's Hankamer School of Business, "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."
To reach the conclusion, 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 write. 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. "Less impulsive individuals who shop most aisles tend to spend the money available from in-store slack but don't exceed their overall budgets. In contrast, in-store slack leads to overspending for highly impulsive individuals who shop most aisles," the authors explain.