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CHAPTER 4 104 Table 1. Also, no pre-test differences were found on any of the dependent variables, largest F (2,86) = 2.54, p = .09. To check whether the manipulation was effective, we examined whether the amount of items participants checked (Checklist) changed from pre- to post-test, and whether the experimental and monitor group differed in scores on the Checklists they filled in each day during the week between the pre- and post-test. Overall, there was a pre- to post-test increase in the amount of items checked, F (1,86) = 82.18, p < .001, η p ² = .49, which differed between conditions, F (2,86) = 146.58, p < .001, η p ² = .77, see Table 1. The effect of Condition was also significant, F (2,86) = 42.13, p < .001, η p ² = .50. Planned comparisons showed an increase in the experimental group, t (29) = 13.42, p < .001, d = 2.92; a decrease in the monitor group, t (28) = 3.49, p = .002, d = 0.44; and no change in the control group, t (29) = 1.30, p = .20. This change in Checklist scores differed between the experimental and monitor group, t (44.30) = 13.47, p < .001, d = 3.47; the experimental and control group, t (38.66) = 12.89, p < .001, d = 3.33; and there was a trend for a difference between the monitor and control group, t (57) = 1.89, p = .05, d = 0.51. On each day during the week between the pre- and the post-test, participants in the experimental group ( M = 74.42, SD = 18.34) checked more items than participants in the monitor group ( M = 18.24, SD = 13.86), t (57) = 13.24, p < .001, d = 3.45. No participants were excluded from analyses because of giving socially desirable answers when filling in the daily Checklists. A low percentage of socially desirable answers was reported by participants in both the experimental ( M = 22.47%, SD = 24.22) and monitor group ( M = 10.31%, SD = 11.84), and they indicated to have performed most of the checking behavior that they had filled in on the daily Checklists (experimental group M = 89.37%, SD = 8.41; monitor group M = 91.34%, SD = 14.70).