 NCEE 2008-4026August 2008 List of Tables

Table 7.1.  Required School Sample Sizes to Detect Target Effect Sizes, for Various RD Designs

Assumes a Two-Tailed Test, a Value of .15 for the Intraclass Correlations, the Cutoff Score Is at
the Center of the Normal Score Distribution and a Balanced Allocation of the Research Groups
Unit of Treatment Assignment: Other
Fixed or Random Effects
Number of Schools Required to Detect an
Impact in Standard Deviation Units of:
.20 .25 0.33
I: Students Within Sites (Schools or Districts): Site Effects Fixed
R2 = 0 39 25 14
R2 = .2 31 20 12
R2 = .5 20 13 7
R2 = .7 12 8 4
II: Classrooms Within Schools: Fixed School Effects
R2 = 0 141 90 52
R2 = .2 113 72 41
R2 = .5 71 45 26
R2 = .7 42 27 16
III: Schools: Within Districts: No Random Classroom Effects
R2 = 0 357 229 131
R2 = .2 286 183 105
R2 = .5 179 114 66
R2 = .7 107 69 39
IV: Students Within Schools: Random Site Effects
R2 = 0 63 40 23
R2 = .2 50 32 18
R2 = .5 31 20 12
R2 = .7 19 12 7
V: Classrooms Within Schools: Random School Effects
R2 = 0 165 105 61
R2 = .2 132 84 48
R2 = .5 82 53 30
R2 = .7 49 32 18
VI: Schools Within Districts: Random Classroom Effects
R2 = 0 459 294 169
R2 = .2 367 235 135
R2 = .5 230 147 84
R2 = .7 138 88 51
Note: See the text for formulas and other assumptions underlying the calculations. The figures assume that the assignment scores are normally distributed.