Glass shapes that make us drink too much

Researchers from Cornell University and the Georgia Institute of Technology have shown that people pour 20-30 percent more alcohol into short, wide glasses than into tall, narrow ones of the same volume. So, as New Year's Eve is coming, remember to use only tall glasses for your party!!!

Some people think that a glass is half empty while others see it as half full. But one thing is sure: some glasses are fuller than others. According to the British Medical Journal (BMJ), researchers from Cornell University and the Georgia Institute of Technology have shown that short glasses are more likely to lead to over-indulgence. In fact, people pour 20-30 percent more alcohol into short, wide glasses than into tall, narrow ones of the same volume. The researchers obtained similar results with students and professional bartenders. So, as New Year's Eve is coming, remember to use only tall glasses for your party!!!

This study has been conducted by Brian Wansink from Cornell University and Koert van Ittersum his colleagues at the Georgia Institute of Technology. And the researchers don't think the reason for overpouring has anything to do with education, practice, or experience, as they say in Cornell University news release.

The reason for the difference, Wansink speculates, is the classic vertical-horizontal optical illusion: People consistently perceive equally sized vertical lines as longer than horizontal ones.
"People generally estimate tall glasses as holding more liquid than wide ones of the same volume," Wansink said. "They also focus their pouring attention on the height of the liquid they are pouring and insufficiently compensate for its width."

Below is a photograph on one of the researchers in front of two glasses. But which one contains the most liquid? (Credit: Brian Wansink and Koert van Ittersum).

Which glass contains the most liquid?

This study involved 198 college students from the University of Illinois at Urbana-Champaign and 95 Philadelphia bartenders. Here are some details about the study provided by the BMJ.

Both students and bartenders poured more into short, wide glasses than into tall, slender glasses. Among students, practice reduced the tendency to overpour into tall glasses, but not into short, wide glasses. Most students also believed that the tall glasses held more.
Despite an average of six years of experience, bartenders poured 20.5% more into short, wide glasses than tall, slender ones. Paying careful attention reduced but did not eliminate the effect.

The following diagram shows that these professional bartenders pour more alcohol in short wide glasses than in tall and slender ones (Credit: Brian Wansink and Koert van Ittersum).

Pouring by bartenders into glasses of different shapes

This research work has been published by the British Medical Journal under the name "Shape of glass and amount of alcohol poured: comparative study of effect of practice and concentration" (Vol. 331, Issue 7531, Pages 1512 - 1514, December 24, 2005). Here are two links to the abstract and the full paper (PDF format, 4 pages, 119 KB). The illustrations above have been extracted from this document.

After reading this paper, a question remains: what to do to avoid overpouring alcohol? The researchers suggest to avoid wide glasses and to use instead tall, narrow glasses or ones on which the alcohol level is marked.

Please don't forget their advise for New Year's Eve!!!

Sources: British Medical Journal news release, via EurekAlert!, December 22, 2005; and various web sites

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