This paper traces the conceptual foundations of the Brunswik based Social Judgment Theory. The historical transition from measurement through probability of responding (i.e., a constancy ratio) to measurement via correlations is documented. It is shown that there are substantive limitations with the correlation approach for the idiographic analysis of human perception or decision-making. Instead, the constancy ratio developed originally by Brunswik as well as the measurement of the probability of accuracy in responding are better suited to the analysis of human responding under conditions of uncertainty and complexity. These measures are relevant for the development of psychological laws of individual responding. It was concluded that focusing on the probability of individual responses to situations through analysing the pattern of responding intensively is more consistent with the original approach of Brunswik.