handout - Daina Chiba

3.4 Plotting Substantive Effects: When X is a Discrete Variable...
If the regressor of your interest takes only a limited number of discrete values (for example,
0 or 1), then consider using histograms instead of line plots. An example of histogram
representation of substantive effects are shown in Figure 2. To produce this figure, run the
R code under section 3.4 and you will obtain (output/figs/subeff2.pdf)
Frequency
0 100 200 300 400
Noncontiguous dyads
Contiguous dyads
0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07
Probability of MID Onset
Figure 2: The effect of geographic contiguity on the probability of MID onset
The figure illustrates the effect of contiguity on the probability that a pair of states experience militarized
interstate disputes between one another. The black histogram located to the left shows the distribution
of predicted probability of MID onset for dyads that do not share a geographic border, whereas the gray
histogram to the right shows that for contiguous dyads. All the covariates other than the contiguity variable
is held at their median (binary variables) or mean (continuous variables) values. Uncertainty estimates are
obtained by resampling 1000 draws of β coefficients from the sampling distribution reported in Figure 4.
17