The odd-even effect in addition: an analysis per problem type.

The odd-even effect is a well documented finding in the literature on mental arithmetic, at least for multiplication. It implies that false answers with the same parity as the correct answer are rejected more slowly than false answers with a different parity. For addition, this effect is not so well documented. The study by Krueger and Hallford (1984) is the only one that investigated odd-even effects for addition. However, they did not investigate odd-even effects per problem, even though there are indications that problem type can modulate odd-even effects for multiplication (Lemaire & Reder, 1999). Therefore, we wanted to get more insight into odd-even effects for addition by investigating odd-even effects per problem type. Our results extended the findings of Krueger and Hallford. First of all, we found an interaction between split and problem type. The most important and new result of present study, however, was a strong parity effect for E + E problems. We discuss our results in terms of two alternative explanations for odd-even effects, namely use of a parity rule on the one hand and familiarity with even outcomes on the other.