A critique is offered of the theory by M. Oaksford and N. Chater (1994
) of rational analysis in P. C. Wason's (1966) selection task. That th
eory turns on the idea that participants choose among different cards
according to the amount of information they expect to gain; however, O
aksford and Chater have chosen a measure of information (the Shannon-W
iener measure) that is irrelevant to the question actually put to the
participants. Consequent to that choice, certain assumptions and param
eter values are dictated by the rank order of selection frequencies th
at the theory seeks to match. Those relationships are picked out, and
the mathematical assumptions are identified and transposed into their
psychological equivalents. Those psychological equivalents are (a) mor
e in number than the results to be explained and (b) psychologically i
mplausible. Finally, a correct Bayesian analysis of the selection task
is shown to confirm the prescription of propositional logic.