Title:      The Importance of Fully Testing Conditional Theories
Positing Interaction

Authors:    Matt Golder, William Berry, Daniel  Milton

Entrydate:  2009-07-10 21:00:23

Keywords:   

Abstract:   In recent years, it has become common for political
scientists to present marginal effect plots when interpreting
results from interactive models. This has led to a dramatic
improvement in the quality of research testing conditional
theories. The typical practice is to (i) view one of the
variables expected to interact, say Z, as the conditioning
variable, (ii) offer a hypothesis about how the marginal effect
of the other variable, X, is conditional on the value of Z, and
(iii) construct a plot of the relationship between Z and the
estimated marginal effect of X. All interactions are symmetric,
though; when the effect of X is conditional on Z, the effect of
Z must be conditional on X. In this paper, we illustrate that
the failure of scholars to provide a second hypothesis about how
the marginal effect of Z is conditional on the value of X,
together with the corresponding marginal effect plot, means that
scholars often subject their conditional theories to
substantially weaker empirical tests than their data allow. The
result is that much of the existing literature either
understates or, more worryingly, overstates the empirical
support for the conditional theories that political scientists
have posited.

http://polmeth.wustl.edu/retrieve.php?id=913

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