Goodie, A. S., & Fantino, E. (1999).
Base rates versus sample accuracy: Competition for control in human matching to sample.
Journal of the Experimental Analysis of Behavior,
71, 155-169.
People often place undue weight on specific sources of
information (case cues) and insufficient weight on more
global sources (base rates) even when the latter are
highly predictive, a phenomenon termed base-rate neglect.
This phenomenon was first demonstrated with paper-and-pencil
tasks, and also occurs in a matching-to-sample procedure in which
subjects directly experience case sample (cue) accuracy and base
rates, and in which discrete, nonverbal choices are made. In two
nonverbal experiments, subjects were exposed to hundreds of
trials in which they chose between two response options that were
both probabilistically reinforced. In Experiment 1, following one
of two possible samples (the unpredictive sample), either
response was reinforced with a .5 probability. The other sample
(predictive) provided reinforcement for matching on 80% of the
trials in one condition but in only 20% of the trials in another
condition. Subjects' choices following the unpredictive sample
were determined primarily by the contingencies in effect for the
predictive sample: If matching was reinforced following the
predictive sample, subjects tended to match the unpredictive
sample as well; if countermatching the predictive sample was
generally reinforced, subjects tended to countermatch the
unpredictive sample. These results demonstrate only weak control
by base rates. In Experiment 2, base rates and sample accuracy
were simultaneously varied in opposite directions to keep one set
of conditional probabilities constant. Subjects' choices were
determined primarily by the overall accuracy of the sample, again
demonstrating only weak control by base rates. The same pattern
of choice occurred whether this pattern increased or decreased
rate of reinforcement. Together, the results of the two
experiments provide a clear empirical demonstration of base-rate
neglect.
Key words: matching to sample, base-rate neglect, base rates,
sample accuracy, choice, key press, adult humans