Margins plots
New in Stata 12 is the marginsplot command, which makes it easy to
graph statistics from fitted models. marginsplot graphs the results
from margins,
and margins itself can compute functions of
fitted values after almost any estimation command, linear or nonlinear.
Suppose we’ve just fit a two-way ANOVA of systolic blood pressure on
age group, sex, and their interaction. We can estimate the response for
each cell with margins:
To study the interaction it would be nice to see a graph. In Stata 12 we no
longer have to construct the graph manually; we can instead just type
marginsplot:
marginsplot automatically chooses the y-variable and x-variable and
adds confidence intervals. We don’t have to stick with the defaults,
though: marginsplot includes a rich set of options for changing axis
definitions, labels, curves, confidence intervals, and more.
marginsplot also supports the new features of the margins
command, including the contrast operators.
Let’s contrast women with men in each age group and plot the
contrasts:
We see that systolic blood pressure is lower in younger women than in
younger men. But among the old, the relationship is reversed, and women
have higher blood pressure than men.
marginsplot works with nonlinear models, too. Suppose we've fit
a logistic regression, modeling the probability of high blood pressure
as a function of sex, age group, body mass index, and their interactions.
marginsplot can contrast women with men on the probability scale:
. quietly margins r.sex, at(bmi=(10(1)65))
. marginsplot, xlabel(10(10)60) recast(line) recastci(rarea)
Variables that uniquely identify margins: bmi
We’ve only scratched the surface—anything that margins
can compute, marginsplot can graph.
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See
New in Stata 12
for more about what was added in Stata Release 12.
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