Distinguishing Between Random and Nonrandom Events

Abstract

Subjects judged whether binary strings had been generated by a random or a nonrandom process. Half of the strings were generated by a Bernoulli process with p = .5. The other half were generated by either a repetition-biased process or an alternation-biased process. Subjects were (a) not informed about the nonrandom process, (b) informed about the qualitative nature of the process, or (c) given accurate feedback after each trial about the generating process. The data show that subjects equate long runs and symmetry with nonrandomness, and high rates of alternation with randomness, making them less successful in detecting alternation-biased processes. The data also show that performance can be improved by instructions or feedback. A second experiment using statistically sophisticated subjects showed that although they perform better than naive subjects, their data are similar qualitatively. We interpret these results in terms of whether the subject must perform the task in a null hypothesis mode or a maximum likelihood mode. © 1987 American Psychological Association.