Something Doesn’t Add Up: How marketers can take advantage of consumers’ innumeracy

The Economist:

WHEN retailers want to entice customers to buy a particular product, they typically offer it at a discount. According to a new study to be published in the Journal of Marketing, they are missing a trick.
A team of researchers, led by Akshay Rao of the University of Minnesota’s Carlson School of Management, looked at consumers’ attitudes to discounting. Shoppers, they found, much prefer getting something extra free to getting something cheaper. The main reason is that most people are useless at fractions.
Consumers often struggle to realise, for example, that a 50% increase in quantity is the same as a 33% discount in price. They overwhelmingly assume the former is better value. In an experiment, the researchers sold 73% more hand lotion when it was offered in a bonus pack than when it carried an equivalent discount (even after all other effects, such as a desire to stockpile, were controlled for).

Related: Math Forum.