Approximately one-third of international business (IB) articles include conditional hypotheses, yet the vast majority risk errors in testing or interpreting the results. Scholars typically restrict their empirical analysis to the coefficient of the interaction term in the regression, exposing themselves to the hazard of overstating or understating results. To mitigate the risk of misstating, we advocate that IB scholars also evaluate the statistical significance of the marginal effect of the primary independent variable over the range of values of the moderating variable. We demonstrate that overstating results can occur when the interaction term coefficient is statistically significant but the marginal effect is not significantly different from zero for some value(s) of the moderating variable. Understating can occur when the interaction term coefficient is not statistically significant, but the marginal effect is statistically different from zero for some value(s) of the moderating variable. In this article, we describe, using simulated data, these two possibilities associated with testing conditional hypotheses, and offer practical guidance for IB scholars.
In “Understating and Overstating Interaction Results in International Business Research,” we identify two important questions for scholars with conditional hypotheses. Question 1 asks whether there is a statistically discernible difference between the marginal effect of a primary explanatory variable across different values of the moderating variable. Question 2 asks if the marginal effects of the primary explanatory variable statistically different from zero, for one, both, or neither level of the moderating variable. We advocate that scholars assess both questions. (Rarely, there may be theoretical reason to only answer Question 1 or Question 2.)
Understating may occur if researchers discard a conditional hypothesis based on obtaining a non-significant coefficient on the interaction term (Question 1), because they may miss seeing a statistically significant non-zero marginal effect of the primary explanatory variable for some value(s) of the moderating variable (Question 2). Overstating may occur if researchers go no further than to report a statistically significant interaction coefficient when, simultaneously, the marginal effect of the primary explanatory variable for one or more values of the moderating variable is not different from zero.
In the JWB article, we propose the following recommendations for scholars.
1. State the conditional hypothesis so as to clearly articulate whether marginal effects (i.e., relationships between the primary explanatory variable and the dependent variable) differ from one another for any two values of the moderating variable (Question 1) and/or whether a marginal effect differs from zero for any specific value of the moderating variable (Question 2).
2. Properly specify the regression model by including the primary explanatory variable X and moderating variable Z, the interaction term XZ, and all relevant control variables (e.g., Equation 1).
Y = β0 + β1X + β2Z + β3XZ + controls
3. Answer Question 1 by evaluating the statistical significance of to ascertain whether the marginal effects are different from each other.
a. Recognize that a statistically significant provides evidence that marginal effects are discernibly different from one another.
b. Recognize that a statistically non-significant provides evidence that marginal effects are not discernibly different from one another.
4. Answer Question 2 by evaluating whether the marginal effects ( = β1 + β3Z ) are statistically different from zero.
a. For a dichotomous moderating variable Z, create a table of marginal effects similar to Table 3. See Files 1 and 2 below.
b. For a continuous moderating variable Z, create a figure similar to Figure 1 or 2, in which a confidence interval is constructed around the marginal effect line over the entire range of the moderating variable. See Files 1 and 3 below.
5. Report both the statistical significance of the coefficient estimate for (Question 1) and the range of values of the moderating variable Z and percentage of observations for which marginal effects attain statistical significance (Question 2).
6. Discuss the level of support (e.g. full, partial, none) for the conditional hypothesis given the statistical results of both questions.
All Stata code to replicate the data, tables, and graphs presented in this paper is available here.
File 1: .do file to replicate the independent variables generated for the simulation analysis.
File 2: .do file to replicate data generating process for dependent variables in the simulation analysis, and results from regressions and marginal effects.
File 3: .do file to replicate figures with embedded histograms for exploring marginal effects over range of values of Innovation. ** These commands are extensions of earlier code made available by Matt Golder.
Interaction Articles Cited in Article:
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