CONJUNCTION ERRORS IN THE PREDICTION OF REFERENDUM OUTCOMES - EFFECTSOF ATTITUDE AND REALISM

Most studies of so-called 'conjunction' errors in probabilistic thinki ng have asked people to estimate the probabilities of hypothetical, or fictional events. In a previous study, we found conjunction errors to occur, although less frequently, in a real-life prediction task (conc erning Norway's chances in three upcoming World Cup soccer games). In the present study, Norwegian voters were asked to evaluate the chances of a final YES or NO to the European Union in the 1994 referendums in Finland, Sweden, and Norway, separately and in combination. Despite t he familiarity of the issue, a large majority committed conjunction er rors, e.g. by rating YES in both Sweden and Norway equally or more lik ely than YES in Norway. The results indicate that conjunction errors a re not reduced by realism and familiarity, at least not for events tha t are seen as causally determined. They are, however, affected by outc ome valence. We found as predicted fewer conjunction errors with negat ive than with positive events. Pro-EU subjects committed fewest errors with NO-conjunctions, whereas anti-EU subjects produced fewer errors with YES-conjunctions.