Illusory correlations

While our species name, Homo sapiens, implies we are “wise”, we are not always rational thinkers. As your study of the Cognitive Approach has shown, we are subject to biases in thinking and decision-making. One such bias is a tendency to identify correlations where there are none. This tendency was investigated by Hamilton and Gifford (1976). Hamilton and Gifford introduced their participants to two groups, one large Group A (which was made up of 26 people) and one small Group B (which was made up of 13 people). So, the participants read about 39 individuals, one at a time. They were informed about each individual’s group membership and about a behaviour performed by that individual. For example, they read “Bruce, a member of Group A, did volunteer work for a church” or “Joe, a member of Group B, made his friend very uncomfortable by his sarcastic remarks”. The behaviours that the group members performed were either positive, helpful behaviours or negative, hurtful behaviours.

The information about the group members was created such that Group A was twice as big as Group B (that is 26 members versus 13 members) and positive behaviours were more than twice as common than negative ones. Said differently, the ratio of positive to negative behaviours was identical for both groups. Have a look at the table below and focus for now on the columns labelled ‘Actual’. That is the actual ratio of helpful to hurting behaviours was identical for both groups (i.e. 9:4).