 Reliable change index

A change score scaled by its expected measurement error. With equal marginal standard deviation $s$, reliability $r$ and independent measurement errors at the two assessments, the difference has error standard deviation $s\sqrt{2(1-r)}$, givingA conventional normal-error criterion compares its magnitude with 1.96. The assumptions and instrument-specific reliability matter; reliable change is not itself diagnostic remission or proof that treatment caused the change.