The odd-even effect in multiplication: Familiarity with even numbers or a parity rule after all?

This study investigated two possible explanations for the odd-even effect in simple arithmetic. This effect is well documented for multiplication. and implies that an incorrect proposed answer in a verification task is rejected faster if the parity of that answer is different from the parity of the correct answer. The explanation based on the parity rule (Krueger. 1986) contends that subjects (implicitly) use the information that the parity, of incorrect and correct answers diverge. The second explanation is based on familiarity with even numbers (Lochy, Seron, Delazer, & Butterworth. 2000). Three fourths of the possible products have indeed an even outcome. so that. according to the familiarity hypothesis, rejecting a wrong even answer is more difficult than rejecting a wrong odd answer. In this study, we conducted a straightforward test of both accounts by presenting as many even as odd incongruent/coagruent answers. A main congruency effect which did not inter-act with problem type was found. The congruency effect on 0 x 0 problems. however. was not significant. The study concludes that (1) the evidence arguers against the familiarity hypothesis: (2) the parity rule cannot be generalized to all problem types but is restricted to certain types of problems: and (3) the findings on problems with two odd multipliers leave the possibility for a limited familarity with even numbers.