The impact of presentation format on causal inferences

The impact of the presentation format of covariation information on causal judgements was examined in a fictitious virus-disease causal induction task. Six different judgement conditions were created by crossing two levels of virus-disease covariation (0, .5) with three levels of disease base rate (.25, .5, .75). The covariation information was presented differently to three groups of participants. In a first group, it was presented in propositional format summarising the frequencies of the four patient types, namely patients with or without the virus who either did have or did not have the disease. In a second group the same information was presented in a 2×2 table with the cell frequencies represented in terms of countable objects (the presence/absence of virus/disease was shown as schematic faces that varied in expression and colour). In a third group the covariation information was presented in terms of a cumulative frequency tree with the two main branches representing the frequencies of patients with and without the disease which further decomposed into subgroups of those with and without the virus. The ability to discriminate between the levels of covariation was poorest in Group 1; it was significantly improved in Group 2, and was best in Group 3. These results suggest that the format with which covariation information is presented to reasoners exerts a significant influence on causal judgements.