A model of informal reasoning under conditions of uncertainty, the outcome
approach, was developed to account for the nonnormative responses of a
subset of 16 undergraduates who were interviewed. For individuals who
reason according to the outcome approach, the goal in questions of uncertainty
is to predict the outcome of an individual trial. Their predictions take
the form of yes-no decisions on whether an outcome will occur on a particular
trial. These predictions are then evaluated as having been either right or
wrong. Their predictions are often based on a deterministic model of the
situation. In follow-up interviews using a different set of problems, responses
of outcome-oriented participants were predicted. In one problem, their
responses were at variance both with normative interpretations of probability
and with the "representativeness heuristic" (Kahneman & Tversky, 1972).
Although the outcome approach is inconsistent with formal theories of
probability, its components are logically consistent and reasonable in the
context of everyday decision making.