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Twenty‐five adults were administered two tasks involving the data of 12,2X2 matrices. In the first, subjects were invited to make decisions on the basis of data which was presented as involving causal, one‐way relationships. Four groups of subjects were distinguished in the level of their operational thinking. In task 2 the subjects were invited to make judgements on identical data, but presented as involving two‐way noncausal relationships. Results showed changes in the level of thought: subjects employing concrete operations in task 1 regressed to lower levels of thought; subjects employing transitional formal thought in task 1 advanced to fully formal thought in task 2. It was concluded that the first task imposed a ceiling effect on the thought levels of the latter subjects. Results showed that the level of thought employed was a function of the frequency of the data in the cells of the matrices and that the emergence of illogical thought was related to task difficulty.

Two hundred subjects made decisions based on the data of two binary variables, ethnic origin and employment status. They were asked to specify the information necessary and sufficient for making the decision before doing so. Variables studied were: (1) Type of question. Five questions were used, four of which focused on one of the four instances involved (e.g., Which information is necessary to find out ifthere is a connection between Asian immigrants and unemployment?). Question five was unbiased. (2) Type of variable. Half of the subjects found two symmetric variables, and half found one symmetric and one asymmetric variable. (3) Level of correlation. Five different correlations were used, three favoring Asians, one favoring Europeans, and one representing a zero correlation. Subjects made logical decisions that were not influenced by any of the experimental conditions. The selection of information before and after making choices was influenced by all variables except level of correlation. The biased questions produced deviations from normative reasoning; the two symmetrical variables and the process of making decisions encouraged normative reasoning.