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How good are we at judging how much we have drunk? Researchers enrolled a random sample of 160 healthy adult volunteers who drink socially but are not alcoholics. A computer task was designed to measure perceptual judgment of the fullness of a glass. Each participant completed the task twice, once when the glass shown was straight and once when the glass shown was curved. For each glass, the full volume was measured on a scale of 60 so that 30 corresponded to the true half. Here are the ndings in summary format: Variable Count Mean StDev Straight 160 28 l . 50 Curved 160 21 3.05 Diff S-C 160 7 2.85 To test whether people can correctly assess the true half of a straight glass, nd the test statistic A 2: 31.07 m t=31.07