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Table 2 Sample size calculations (calculated using PowerUp!a)

From: Whole School SEND (WSS) Review: study protocol for a two-arm pragmatic parallel cluster randomised controlled trial in 160 English secondary schools

  All pupils SEND pupils FSM pupils
Minimum Detectable Effect Size (MDES) 0.19 0.20 0.19
Pre-test / post-test correlations
 Level 1 (pupil) 0.70 0.70 0.70
 Level 2 (class) n/a n/a n/a
 Level 3 (school) 0.32 0.32 0.32
Intracluster correlations (ICCs)
 Level 2 (class) n/a n/a n/a
 Level 3 (school) 0.20 0.20 0.20
Alpha 0.05 0.05 0.05
Power 0.80 0.8 0.8
One-sided or two-sided? Two Two Two
Average cluster size 180 25 42
Number of schools
 Intervention 80 80 80
 Control 80 80 80
 Total 160 160 160
Number of pupils
 Intervention 14,400 2000 3360
 Control 14,400 2000 3360
 Total 28,800 4000 6720
  1. aPowerUp! https://www.causalevaluation.org/power-analysis.html