The use of intuitive heuristics (e.g. representativeness and availability) has been put forward as an explanation for people's assignment of probabilities (Tversky and Kahneman, 1971). This phenomenon is seen as robust since experts as defined by education (professional psychologists), despite advanced training in statistics and methodology, rely on the same heuristics as novices (lay people). Both experts and novices as defined by education were studied in a series of experiments and further classified as experts and novices according to their probability knowledge base, prior to receiving (or not) a brief (15-minute) training session. Immediately following training, subjects completed a probability test which consisted of ten Tversky and Kahneman (e.g. 1974) problems. The training significantly increased the number of problems correctly solved on the probability test and eliminated the experthovice education classification. The results of a follow-up test 5 weeks after the experiment indicated that the training group maintained its superior performance. It is proposed that failure to use proper methods of probability assignment may not be due to intrinsic human inference biases or heuristics, but is a result of a minimal probability knowledge base.
'Three criteria must be satisfied for a system to be random. First, the event must be repeatable under essentially constant conditions. Second, the relative frequency of the event is seen to converge or approach a limit as the number of repetitions increases. The third criterion is that no rule can be formulated to predict a future outcome of the system. Most games of chance satisfy these three criteria.