The developmental psychologist Jean Piaget developed several tasks to show how very young children were different from older kids. One of the most surprising is the “conservation” task: a 5-year-old, who talks clearly and appears quite bright, will watch water being poured from a short, wide glass into a tall, slender one. She will say that the tall glass has “more” water. A 7-year-old won’t make the same mistake.
Surely, then, adults are aware that short, fat glasses have deceptively large volumes, right? Not according to a recent article in BMJ. Brian Wansink and Koert van Ittersum asked 198 college students to pour shots of “liquor” (actually just dyed water) from a bottle into either short and wide or tall, slender glasses. They were allowed to practice pouring into a standard shot glass first. Here are the results:
The dotted line represents the volume of a shot. While more practice did reduce the volume of liquor poured, it did nothing to reduce the disparity between tall, wide, and short, slender glasses. College students, of legal drinking age, were making the same mistake as Piaget’s 5-year-olds.
College students, however, aren’t generally professional bartenders. Perhaps with years of experience, a bartender can accurately compensate for the width of a glass. Wansink and van Ittersum next offered actual bartenders $4 to try their skill at the task. These bartenders averaged 6.3 years’ experience. Here are their results:
Even bartenders made the same mistake as five-year-olds, pouring more liquid into the short, wide glasses than the tall, narrow ones. The bartenders weren’t offered practice trials, but they were more accurate than college students, and did even better when the experimenter told them to “please take your time” before pouring. However, even when taking care, they still poured significantly more liquor into short, wide glasses than tall, narrow ones.
Wansink and van Ittersum suggest that studies of alcohol consumption should take the shape of the glasses used into account when analyzing the data. Drinkers who favor tumblers over highball glasses may be consuming significantly more. And, if you’re trying to watch how much you drink, you might consider switching to taller, narrower glasses — or precisely measuring out each portion.
Note: The New York Times recently published an article highlighting more of Wansink’s research on how much we think we’re consuming versus what we really do consume. Fascinating stuff.
Wansink, B., & van Ittersum, K. (2005, 24-31 December). Shape of glass and amount of alcohol poured: Comparative study of effect of practice and concentration. BMJ, 331, 1512-1514.