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An Anchoring and Adjustment Model of Purchase Quantity Decisions

Wansink, Brian, Robert J. Kent, and Stephen J. Hoch (1998). An Anchoring and Adjustment Model of Purchase Quantity Decisions. Journal of Marketing Research, 35(1), 71–81.

Numerical signs, such as "2 for $2" or "Limit 12 per person" make you spend twice as much as you planned. Studies conducted by researchers at the Food and Brand Lab found that certain promotions have great effect on the number of goods purchased. The four studies spanned 89 supermarkets and thousands of consumers. The findings were published in the Journal of Marketing Research* .

The research indicates that promotions that utilized multi–unit pricing ("3 for $3"), purchase limits ("Limit 12/person") and suggestive selling ("Buy 10 for your freezer") all doubled the amount consumers purchased – and such promotions can be found throughout grocery stores across the country.

When most people buy products, they buy one or two at a time. They decide on a low number (like one or two), then buy more if the product's on sale. When promotions suggest high numbers ("Buy 12 so you don't run out!"), people shift their reference point to the higher number, and buy more.

"All three types of promotions increase purchase amounts from 30% to 105% of what the consumer would normally plan on buying," said Dr. Brian Wansink, director of the Cornell Food and Brand. "But, consumers can counteract these promotions. They can write their purchase amounts on their shopping lists and stick to it. "

Wansink said that consumers should always be aware of what is really being offered and he offered some "words of wisdom" to consumers.

  • Be aware of what the advertisements and deals really mean for you, know how much you're actually saving and remember that smaller numbers don't always mean a better deal – but neither do the big numbers.
  • Lower limits (two per visit) make consumers buy the product more often while high limits (12 per person) increase the amount of the sale for that visit.
  • Suggestive selling (Grab six for studying) is not a sale. They're just promoting the product.

Wansink said the more aware consumers are, the less likely they are to find themselves with a cabinet full of unneeded and unwanted products.

Download a pre-print version of this article here. Reprinted with permission from Journal of Marketing Research, published by the American Marketing Association.

*The study was conducted at the University of Illinois, former location of the Cornell Food and Brand Lab.