Toward a reconceptualization of the law of initial value.

The traditional model of the law of initial value (LIV), "the higher the initial value, the smaller the response to function-raising, the larger the response to function-depressing stimuli" (Wilder, 1967, p. viii), is critically reviewed. Statistically, the usage of rDX, bDX, and bYX as the indices of LIV contains a spurious X(Y-X) effect. Moreover, defining initial value as a synonym of baseline is too narrow to cover an organism's various states. The parameter of structural relationship beta e value and a null hypothesis test (beta e = 1) are recommended to examine initial-value dependency for different levels of initial value and trends of change. Data suggest that LIV should be revised as follows: The higher the initial value, the greater the organism's following reactivity, although a tendency to reversed responses may occur when the initial value reaches its upper extremity. Both phenomena are probably due to constitutional and homeostatic mechanisms, respectively.