Intuitive t tests: lay use of statistical information.

Normatively, a statistical pairwise comparison is a function of the mean, standard deviation (SD), and sample size of the data. In our experiment, 203 undergraduates compared product pairs and judged their confidence thatone product was better than the other. We experimentally manipulated (within subjects) theaverage productratings, the number of raters (sample size), and the SD of the ratings. Each factor had two levels selected, so that the same change in statistical power resulted from moving from the low to the high level. We also manipulated (between subjects) whether subjects were given only the product rating data as summarized in a statistical format orthe summariesplus the raw ratings. Subjects gave the most weight to mean product ratings, less weight to sample size, and very little weight to SD. Providing subjects with raw data did not increase their use of sample size and SD, as predicted.