Thursday, 5 January 2006

Beware short, wide glasses

If your New Year’s resolution is to drink less, you may find it useful to know that because of perceptual biases, people tend to pour more liquid into short, wide glasses – ‘tumblers’ – than they pour into tall, elongated, ‘highball’ glasses.

Brian Wansink and Koert van Ittersum at Cornell University asked 198 students to pour a shot (44.3 ml) of whiskey, rum, gin or vodka from a full bottle into a glass. The bottles were real, but they actually contained water or tea. The students who poured into short, wide glasses, poured 30 per cent larger shots than the students asked to pour into tall glasses. Moreover, when asked to estimate the capacity of the glasses, the students estimated the tall glass held an average of five per cent more liquid, even though the glasses’ true capacity was actually equivalent. Students who poured into tall glasses were more accurate if they’d been given 10 practice pours with a shot glass, but practice did not improve the accuracy of the students pouring into short, wide glasses.

In a follow-up study, the researchers repeated the procedure with 86 experienced bartenders to see if they too were prone to this bias. Despite their experience, the bartenders poured an average of 20.5 per cent larger shots into short, wide glasses than into tall, slim ones.

The researchers said “If short tumblers lead even bartenders to pour more alcohol than tall highball glasses, the way to better control alcohol consumption is to use tall glasses or to use glasses with the alcohol level marked on them – and to realise that, when alcoholic drinks are served in a short wide glass, two drinks are actually equal to two and a half”.
Wansink, B. & van Ittersum, K. (2005). Shape of glass and amount of alcohol poured: comparative study of the effect of practice and concentration. BMJ, 331, 1512-1514.

Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.

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