The Deceptive Glass

ByABC News

Dec. 28, 2005 — -- New Year's Eve rolls around, and although you know you've already overdone it this holiday season, you settle down with your squeeze and pour a couple glasses of bubbly. This time you swear you're not going to pour too much.

But will you get it right?

That may well depend on the glass you use, according to new research.

If you pour champagne into a tall, slender glass, you'll probably serve yourself less than if you pour it into a short, fat glass. But the human mind plays tricks, so you'll almost surely think it's the other way around.

Brian Wansink, professor of marketing, applied economics and nutritional science at Cornell University, has spent years studying how the shape of containers influences our consumption, and he has weighed in with a new study just in time for New Year's celebrations.

In the study, published in the current issue of the British Medical Journal, Wansink and Koert van lttersum, assistant professor of marketing at Georgia Institute of Technology, demonstrate that even professional bartenders get the amount wrong much of the time, although their expertise improves with experience.

Three separate studies yielded similar conclusions, regardless of the beverage. Teenagers concerned about their health poured less fruit juice when they were given tall, slender glasses than when they were given short, squat tumblers, although they believed the opposite was true.

What is at work here is how we measure quantities in the mind's eye, Wansink says. We tend to rely more on a vertical than a horizontal measurement, so it appears at first that a taller glass holds more than a shorter one, even if the short glass is wider. "Elongation," to use the researchers' word, is the trickster here.

Misgauging quantity isn't just a problem for bartenders. It concerns health-care professionals, fitness advocates, parents and anyone else who wants to take precautions during this hazardous season. It's easy to drink too much this time of the year, and the scientific results that Wansink and others have so carefully acquired are probably somewhat compromised by the fact that many drinkers have become very skilled at getting more than they should.

So there's more here at work than the shape of the glass. The research shows that sometimes we pour more than we think.

In the first of three experiments, 94 teenagers (average age, 15) who attended a summer camp that emphasized health and physical fitness were randomly given juice glasses of different shapes when they entered the cafeteria. Researchers later measured how much the kids had poured, and asked them how much they thought they had poured.

It turned out that those who had been given short, wide glasses poured 74.37 percent more than those who where given tall, slender glasses, "but they perceived themselves as having poured less," the study said.

But regardless of how much they thought they had poured, 97 percent finished the drink, so the short, fat glasses led to more consumption, even though the participants thought they had drunk less.

The second part of the study showed, however, that our judgment improves as we get older, at least when it comes to estimating how much we pour. For this phase, 89 adults, mostly male, who'd attended a weekend camp on jazz improvisation were tested in a cafeteria setting similar to the one used for the teenagers. Ages ranged from 16 to 82, with an average age of 37.2.

As with the teenagers, adults who were given short, fat glasses poured more juice than those who were given tall, slender glasses, but the difference in the numbers was not as dramatic. Adults poured only 19.44 percent more into the short glasses, compared with 74.37 percent more for the teenagers.

But the adults, too, were fooled when it came to estimating how much they had actually poured.

"Of those given short glasses, 79 percent underestimated how much they'd poured compared with 17 percent of those given tall glasses," the study said.

So those with the squat glasses consumed more, even though they believed otherwise.

For the final phase of the study, the researchers called on the pros. And it turned out that bartenders were a lot better at guessing the correct amounts, but even they could get the quantity wrong.

The researchers divided some 45 Philadelphia bartenders into two groups, with one group given tall, slender glasses and the other given short, fat glasses, and asked them to pour exactly 1.5 ounces of alcohol, supplied by the researchers, into the glasses. They also divided the participants into two categories: those with less than five years' experience (2.1 years average) and those with more than five (9.4 years average).

"Despite an average of 5.1 years of experience, bartenders were biased by the elongation of the glasses into which they poured," the study said. "On average, bartenders poured 27.16 percent more into short, wide glasses than into tall, slender glasses."

But that error diminished considerably with more years on the job.

"This tendency was less apparent -- yet still not eliminated -- with more experienced bartenders, who poured an average of 0.15 ounces more into the short glasses than the tall glasses," the study said. And this may come as a surprise to barflies, but "in no case" did the bartenders pour less than 1.5 ounces.

Similar results were found in additional studies including college students and bartenders who were asked to take more time and to pour several times. They still poured too much into short glasses.

The studies all suggest that even when cold sober, those who imbibe can fool themselves.

"People pour more into short glasses than taller glasses, yet they believe the opposite is true," the study concluded.

That would suggest that using tall, slender glasses would reduce consumption, but there's undoubtedly a lot more at work here than just the shape of the glass, especially when it comes to pouring booze.

Maybe the bottom line is more basic. Be careful, be safe, and stay away from short, fat glasses.

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