Table 1.

Reliable change scores and their formulae.

Reliable change score	Formula
RCI	zRCI = (T2 −T1)− (M2 − M1)/SED  SED = √[(S1√1 − r12)2 + (S2√1 − r12)2]
“simple” SRB	T2′ = c + bT1  zSRB = T2 − T2′/SEE
“complex” SRB	T2′ = c + bT1 + other variables in the model  zSRB = T2 − T2′/SEE

Note. RCI = reliable change index; SRB = standardized regression-based model; T₁ = score at Time 1; T₂ = score at Time 2; S₁ = standard deviation at Time 1; S₂ = standard deviation at Time 2; r₁₂ = correlation between Time 1 and 2 scores; M₁ = control group mean at Time 1; M₂ = control group mean at Time 2; SED = standard error of the difference; b = slope of the regression model (beta coefficient for T₁); c = intercept of the regression model (constant); SEE = standard error of the estimate of the regression model; T₂′ = predicted score at Time 2 based on regression model.