"People focus their pouring attention on the height of the liquid they are pouring and insufficiently compensate for its width," explains Koert van Ittersum, an assistant professor of marketing at Georgia Tech College of Management.
Even educating people about this human perceptual tendency and encouraging them to be careful doesn't eliminate alcohol over-pouring, find van Ittersum and Brian Wansink, a professor of marketing, applied economics and nutrition science at Cornell University in the study, "Reducing Alcohol Over-pouring and Underreporting."
They consider their findings relevant to policymakers and law-enforcement officials who want to increase public safety, groups wanting to promote responsible drinking and decrease alcohol abuse, and people in the hospitality industry who want to cut costs (via serving size) without decreasing customer satisfaction.
"If short tumblers lead people - even bartenders - to pour more alcohol than highball glasses, then there are two easy solutions," van Ittersum says. "Either use tall glasses or ones with alcohol-level marks etched on them as is done in some European countries."
The researchers conducted their study using 198 students of legal drinking age at the University of Illinois at Urbana-Champaign who poured mock mixed drinks into both tall and short glasses from liquor bottles filled with water or tea instead of alcohol. Study subjects also included eighty-two bartenders in Philadelphia who had an average of 6.3 years of bartending experience.
Even 10 rounds of practice didn't make close to perfect for students involved in the study. More career experience led bartenders to pour less alcohol into shorter glasses, but they still over-poured. "This tendency is not sufficiently reduced by education, practice, concentration, or experience," van Ittersum says.