Bond criticized the base-free measure of change proposed by Tucker, Damarin, and Messick by pointing to an incorrect derivation which is here viewed instead as a correct derivation entailing an inadequately specified tacit assumption. Bond's revision leads to estimates of the correlation between initial position and change which are negatively biased by correlated errors, whereas the original approach, with the tacit assumption properly denoted, leads to unbiased values.

Tucker, Damarin and Messick proposed a “base-free” measure of change which involves the computation of residual scores that are uncorrelated with true scores on the pretest. The present note discusses this change measure and demonstrates that, because of an incorrect derivation by the authors, properties they attribute to α (the coefficient for the regression of true scores from the second testing on true scores from the first testing) are, in fact, properties of b, the ordinary regression coefficient. A correct derivation of the initial position—change correlation in terms of α is obtained, and Tucker et al.'s discussion of the “law of initial values” is reconsidered.