Unplanned purchases: Why does that Snickers bar looks better the longer you shop?

June 2, 2015, American Marketing Association

You go to the grocery store to buy a pound of ground beef and a can of tomato sauce. You walk out with the ground beef, the sauce, and a bag of chocolate-covered almonds, a silicon spatula, and the latest celebrity magazine. What happened? According to a new study in the Journal of Marketing, what and when you purchased determined the array of items you eventually bought.

"Shoppers enter the planning to buy certain things, but are tempted to buy unplanned items," write authors Timothy J. Gilbride (University of Notre Dame), Jeffrey Inman (University of Pittsburgh), and Karen Melville Stilley (Market Rise Consulting). "Over the course of the shopping trip, the tendency to buy unplanned items increases. As shoppers spend more on planned items, the tendency to purchase unplanned items goes up. Depending on the shopper's budget, the later an unplanned purchase is made, the more likely the next purchase will be unplanned. The likelihood of an unplanned purchase can be as much as 9.6% higher toward the end of the trip."

What sets the current study apart is the way it treats the likelihood of unplanned purchases. In other studies, a shopper's tendency to make an unplanned purchase remains the same throughout the shopping trip. The current study allows that tendency to change as the trip unfolds. Four hundred customers at two grocery stores were approached upon entry and asked how much they expected to spend on planned purchases, and how much they expected to spend overall. Respondents used a handheld scanner to scan the barcode of each item as they placed it into their cart to record the order in which items were selected.

Results showed that shoppers behaved according to one of two theories. One set of shoppers with small budgets (less than $64), behaved consistent with so-called self-regulation theory: an unplanned purchase decreased the probability that the next purchase would be unplanned. However, as the shopping trip progressed, the opposite became true. Medium-budget shoppers (those with budgets between $64 and $109) made purchases consistent with what is known as cuing theory: an unplanned increased the probability that the next item would be unplanned, and the probability only increased during the trip.

"Retailers should consider offering unplanned items to later in their trips, or promoting apps that keep track of shopping and allow the retailer to make targeted suggestions. Consumers, too, should be aware that their urge to make unplanned purchases grows as a shopping trip unfolds, and that using a mental budget or app could help them avoid an unexpectedly large bill while still enjoying a certain amount of impulse buying," the authors conclude.

Explore further: What is in-store slack? Consumers often plan for unplanned purchases

More information: Timothy J. Gilbride, J. Jeffrey Inman, and Karen Melville Stilley. "The Role of Within-Trip Dynamics in Unplanned Versus Planned Purchase Behavior." Forthcoming in the Journal of Marketing.

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