Choice reaction times and response probabilities are analyzed in terms of a random walk decision process. The theory of relative judgment which gives rise to this analysis assumes that a presented stimulus is compared by the subject to an internal psychological standard or referent. Discrepancies between the stimulus and the referent are accumulated until one or the other of two response thresholds is exceeded. Results from three experiments are examined in detail. In each experiment a particular feature of the theory is tested and shown to be supported by the data. Methods of estimating the two parameters of the theory are given and an appendix presents a summary of theoretical results.