Supermarket Scanner Accuracy Checks Out 

People often don't trust supermarket scanners to ring up correct prices. But a researcher in the College of Agricultural Sciences says when it comes to being cheated, you'll never guess who the loser frequently is. An analysis of data from almost 400 supermarkets participating in the Pennsylvania Scanning Certification Program (SCP) revealed that, while there are both overcharges and undercharges in most stores, shoppers were more likely to be undercharged on a scanned item than to be overcharged, says Drew Hyman, professor of public policy and community systems.

"People assume they'll be overcharged when errors are made," Hyman says. "But when we look at errors made in the stores inspected in the last year, we find that 54 percent of the errors are undercharges, 27 percent are overcharges, and 17 percent are items with no price." Hyman says research reveals that the average consumer paid 17 cents less per mismarked item than they would have paid if the prices had been accurate.

"When we look at the composition of errors," Hyman explains, "there's a higher percentage of errors in sale items, frozen foods, and in the health-and-beauty-care section, where they have many items and it's hard to clearly label them. Another area to watch is direct-delivery items such as snacks and potato chips, stocked by someone who's not a store employee. If they don't communicate to the store any changes in prices or sale items, the price in the computer will be incorrect."

While these figures are only for participants in the SCP, other studies show that most Pennsylvania supermarkets typically follow the same pattern: mistakes are more likely to help the shopper's budget than the supermarket's. "Other studies have shown similar results -- errors in almost all cases don't come from the electronics or because someone's trying to cheat you," Hyman says. "Scanners themselves tend to be very accurate. A lot of the errors are due to mispriced tags on items and incorrectly entered prices in the computer that interacts with the scanner, rather than the scanner itself. The errors tend to come outside of the equipment."

Hyman says the Scanning Certification Program checked about 80,000 items -- about 200 items per store -- and discovered that the most common sources of errors are human, not mechanical. For instance, an employee may forget to enter an item's sale price into the computer; when the item is scanned, the old, non-sale price comes up. Errors also are made when a supermarket chain downloads the current prices for items from a computer at the chain's regional office. They even can come from shoppers removing or switching price tags in the aisles.

Hyman tells shoppers to expect an occasional error. The average supermarket's prices are more than 95 percent accurate, and SCP participants average more than 98 percent accuracy. But with most supermarkets stocking between 30,000 and 40,000 items, and bigger facilities exceeding 75,000, mistakes are inevitable. So pay attention at the check-out counter.

The Scanning Certification Program is an independent quality-control system founded in 1991 by a coalition of Pennsylvania food merchants, concerned consumers, labor union representatives, and state regulators. In addition to the independent certification process, it provides an educational program for employees and clear strategies for managers to improve the store's accuracy rating.

"The program is completely voluntary," Hyman says. "It's a good tool to help managers understand what's happening in their store and to assure consumers that they aren't being overcharged. We try to have something in the program that benefits all sides."

Percentage of pricing errors at the supermarket checkout.

For those who yearn for the "good old days" of hand-checking, Hyman says research in the field presents a sobering fact: hand-checking into a cash register typically had an 11 percent error rate, compared to today's 4.5 percent national average for scanning and the 1.5 percent average error rate of SCP participants.

-- Gary Abdullah