Evaluation of Family Preservation and Reunification Programs: Final Report - Volume Two. 1.2.2 Sample Size


Each site was evaluated separately. We initially set a goal of 500 cases in each site, about 250 in each group. To detect a difference of 15 percentage points between the experimental and controls groups in such characteristics as placement rates with a probability of 0.8 (directional hypothesis, centered on 50%) we would require a total of about 275 cases in both groups. We set our goal higher in order to be able to do some subgroup analyses with adequate power. Initially we hoped to enroll 500 families in each site over a one-year period. However, the sample accumulation in sites in this report, Kentucky, New Jersey, Tennessee, and Philadelphia was slower than expected. A 349-case sample size was achieved in Kentucky after enrolling families for two years. In New Jersey, 442 net cases were enrolled over an 18-month period and in Tennessee, 147 net cases were enrolled over a 21-month period. In Philadelphia, we obtained a sample of 353 cases over a 26-month period.

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