A long history of psychology research has demonstrated that memory is usually improved by studying material on multiple occasions rather than one time only. This effect is commonly known as distributed practice, or spacing effects. In a recent paper examining this effect, Cepeda et al. (2008) looked at the influence of different delays or gaps between study sessions. The results suggest that optimal long-term memory occurs when the study periods are spaced one to three weeks apart. In one part of the study, a group of participants studied a set of obscure trivia facts one day, returned the next day for a second study period, and then was tested five weeks later. A second group went through the same procedure but had a one-week gap between the two study sessions. The following data are similar to the results obtained in the study. Do the data indicate a significant difference between the two study conditions? Test with α = .05, two-tailed.

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One-Day Gap between Study Sessions n = 20 M = 26.4 SS = 395 One-Week Gap between Study Sessions n = 20 M = 29.6 SS = 460