A re-examination of “bias” in human randomness perception

Human randomness perception is commonly described as biased. This is because when generating random sequences humans tend to systematically under- and over-represent certain subsequences relative to the number expected from an unbiased random process. In a purely theoretical analysis we have previously suggested that common misperceptions of randomness may actually reflect genuine aspects of the statistical environment, once cognitive constraints are taken into account which impact on how that environment is actually experienced (Hahn & Warren, Psychological Review, 2009). In the present study we undertake an empirical test of this account, comparing human-generated against unbiased process-generated binary sequences in two experiments. We suggest that comparing human and theoretically unbiased sequences using metrics reflecting the constraints imposed on human experience provides a more meaningful picture of lay people’s ability to perceive randomness. Finally we propose a simple generative model of human random sequence generation inspired by the Hahn & Warren account. Taken together our results question the notion of bias in human randomness perception.