Retail web sites that have a field to enter a discount code at checkout are driving away customers who are ready to make a purchase but do not have a discount code, according to new research from the Owen Graduate School of Management at Vanderbilt University.

“Our study revealed a shopper will not bother to complete the purchase because he or she believes there is a perceived inequality or injustice that someone else is getting a better deal than they are,” says Mikhael Shor, Owen-Vanderbilt assistant professor of economics and co-author of the study along with Richard L. Oliver, professor of management. “It`s a question of haves versus have-nots.”

Shor devised a test in which consumers searched for then placed a product into a shopping cart at the fictitious ToyMart.com. Of customers who had a discount code, 76% bought the product. For those who did not have a discount code, only 19% bought.

Shor says online discounts remain a mystery to most consumers because they do not know how to obtain promotion codes, let alone how to use them, thus deterring purchases. The study also says consumers also have no idea how the coupons are distributed.

The Owen-Vanderbilt study also saw a direct correlation between a consumer’s belief that searching for online coupons is worth the time, and the technical expertise of the shopper. “Unlike traditional coupons, the time involved in searching for promotion codes varies greatly with the skill of the computer user,” Oliver says.

“Many web sites are now devoted to locating online coupons, and codes are clearly visible in summaries provided by search engines, a location familiar to regular Internet users,” he said. However, Shor believes that most companies could not consistently deliver promotion codes to targeted markets successfully, given the availability of the codes on multiple web sites, which are outside retailers’ control.