TY - JOUR

T1 - Improving tests of theories positing interaction

AU - Berry, William D.

AU - Golder, Matt

AU - Milton, Daniel

PY - 2012/7

Y1 - 2012/7

N2 - It is well established that all interactions are symmetric: when the effect of X on Y is conditional on the value of Z, the effect of Z must be conditional on the value of X. Yet the typical practice when testing an interactive theory is to (1) view one variable, Z, as the conditioning variable, (2) offer a hypothesis about how the marginal effect of the other variable, X, is conditional on the value of Z, and (3) construct a marginal effect plot for X to test the theory. We show that the failure to make additional predictions about how the effect of Z varies with the value of X, and to evaluate them with a second marginal effect plot, means that scholars often ignore evidence that can be extremely valuable for testing their theory. As a result, they either understate or, more worryingly, overstate the support for their theories.

AB - It is well established that all interactions are symmetric: when the effect of X on Y is conditional on the value of Z, the effect of Z must be conditional on the value of X. Yet the typical practice when testing an interactive theory is to (1) view one variable, Z, as the conditioning variable, (2) offer a hypothesis about how the marginal effect of the other variable, X, is conditional on the value of Z, and (3) construct a marginal effect plot for X to test the theory. We show that the failure to make additional predictions about how the effect of Z varies with the value of X, and to evaluate them with a second marginal effect plot, means that scholars often ignore evidence that can be extremely valuable for testing their theory. As a result, they either understate or, more worryingly, overstate the support for their theories.

UR - http://www.scopus.com/inward/record.url?scp=84864479679&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84864479679&partnerID=8YFLogxK

U2 - 10.1017/S0022381612000199

DO - 10.1017/S0022381612000199

M3 - Article

AN - SCOPUS:84864479679

VL - 74

SP - 653

EP - 671

JO - Journal of Politics

JF - Journal of Politics

SN - 0022-3816

IS - 3

ER -