1. Statistical Analysis of the Regression Point Displacement Design (RPD)

2. Statistical Requirements
N(n=1) O X O
N O O
Pre-post
Two groups, but one group has n=1
Dummy-code treatment variable
Analysis of Covariance model

3. RPD Example . 7 1 . 6 Y . 5 . 4 . 3 . 3 . 4 . 5 . 6 . 7 . 8 X

4. Regression Model for Analysis of Covariance
yi = 0 + 1Xi + 2Zi + ei
where:
yi = outcome score for the ith unit
0 = coefficient for the intercept
1 = pretest coefficient
2 = mean difference for treatment
Xi = covariate
Zi = dummy variable for treatment (0 = control, 1= treatment[n=1])
ei = residual for the ith unit

5. RPD Example The regression equation is Y = 0.0120 + 0.784 X - 0.0199 Z
Predictor Coef Stdev t-ratio p
Constant X Z
s = R-sq = 72.6% R-sq(adj) = 70.6%

6. RPD Example . 7 1 . 6 Y . 5
2= . 4 . 3 . 3 . 4 . 5 . 6 . 7 . 8 X