= R emmeans =

'''emmeans''' is a package for calculating estimated marginal means.

<<TableOfContents>>

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== Installation ==

[[R/InstallingPackages|Install]] the `emmeans` package.

{{{
install.packages('emmeans')
}}}

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== Usage ==

Given a model fit by e.g., [[R/BuiltinFunctions/Lm|lm]], try:

{{{
emmeans(mod, specs = ~ treatment)
}}}

The `specs` option specifies the marginal means to calculate.
 * Can instead pass a vector of variable names, as in `specs = c("foo", "bar", "baz")`
 * If a specified variable is continuous, one marginal mean is calculated at the mean.
 * If a specified variable is a factor, a marginal mean is calculated for each level.

If the sample should be split by some group variable before calculating marginal means, for example because the model estimated the interaction of a treatment and the group identifier, then try:

For e.g. a [[Statistics/AnalysisOfVariance#Two-way_ANOVA|two-way ANOVA]], it's often desirable to calculate the marginal means for one factor holding the second factor constant. Try:

{{{
mod <- lm(y ~ factor1 * factor2, data=df)

emmeans(mod, specs = ~ factor1 | factor2)
#or
emmeans(mod, specs = ~ factor1, by="factor2")
}}}

Calculate pairwise comparisons as:

{{{
pairs(emmeans(mod, specs = ~ treatment))
}}}

The `adjust` option determines what adjustments are applied to test statistics. If unset, by default [[Statistics/TukeysRangeTest|Tukey's adjustment]] is used. Alternative options are `"none"` and `"bonferroni"`.

`pairs` returns an object that can be passed to the [[R/BuiltinFunctions/Plot#emmeans|plot]] function.



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