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We looked at whether, when, and how grocery shoppers keep track of their in–store spending in order to determine if how consumers stay within their budgets. We conducted a field study of 293 shoppers at two Atlanta supermarkets, one of which was in an area with a 35.7% poverty rate and one with a 14.3% poverty rate.
We found that shoppers in the lower–income area are more likely to keep track of their spending and identified three tracking strategies: mental computation, calculators, and shopping lists.
A laboratory study of 126 undergraduates was conducted in which participants were asked to estimate the total price of a shopping basket. Four different price–ending conditions were used to determine how price–endings influenced estimation behavior. We found that most participants relied on computation estimation strategies, which were more successful than exact calculations except in the case where shoppers consistently rounded up price–endings > $0.51. In a second laboratory study of 209 undergraduates, we examined the effect of motivation and estimation experience on estimation behavior and performance. Half of the participants were given a cash incentive of up to $5 based on the accuracy of their estimates. The rest of the procedure was identical to the first laboratory study. We found that more motivated shoppers are more inclined to calculate the exact total basket price, although this causes their estimates to be less accurate.
Thus, trying to motivate a shopper to be more accurate is likely counterproductive and increases bias. However, motivation does improve performance among more experienced shoppers compared to less experienced shoppers. A second supermarket study confirmed that budget shoppers are twice as likely to track their in–store spending than those who shop without a budget. Overall, we conclude that price–endings influence estimation behavior and performance and that motivated shoppers try harder, but do worse.
Van Ittersum, Koert, Joost M.E. Pennings, and Brian Wansink (2010). Trying Harder and Doing Worse: How Grocery Shoppers Track In–Store Spending. Journal of Marketing, 74(2), 90-104. doi: http://dx.doi.org/10.1509/jmkg.74.2.90