Estimated Marginal Means, aka Least-Squares Means


License
GPL-2.0+

Documentation

R package emmeans: Estimated marginal means

Note: emmeans is a continuation of the package lsmeans. The latter will eventually be retired.

Features

Estimated marginal means (EMMs, previously known as least-squares means in the context of traditional regression models) are derived by using a model to make predictions over a regular grid of predictor combinations (called a reference grid). These predictions may possibly be averaged (typically with equal weights) over one or more of the predictors. Such marginally-averaged predictions are useful for describing the results of fitting a model, particularly in presenting the effects of factors. The emmeans package can easily produce these results, as well as various graphs of them (interaction-style plots and side-by-side intervals).

  • Estimation and testing of pairwise comparisons of EMMs, and several other types of contrasts, are provided. There is also a cld method for display of grouping symbols.

  • Two-way support of the glht function in the multcomp package.

  • For models where continuous predictors interact with factors, the package's emtrends function works in terms of a reference grid of predicted slopes of trend lines for each factor combination.

  • Vignettes are provided on various aspects of EMMs and using the package. See the CRAN page

Model support

  • The package incorporates support for many types of models, including standard models fitted using lm, glm, and relatives, various mixed models, GEEs, survival models, count models, ordinal responses, zero-inflated models, and others. Provisions for some models include special modes for accessing different types of predictions; for example, with zero-inflated models, one may opt for the estimated response including zeros, just the linear predictor, or the zero model. For details, see vignette("models", package = "emmeans")

  • Various Bayesian models (carBayes, MCMCglmm, MCMCpack) are supported by way of creating a posterior sample of least-squares means or contrasts thereof, which may then be examined using tools such as in the coda package.

  • Package developers may provide emmeans support for their models by writing recover_data and emm_basis methods. See vignette("extending", package = "emmeans")

Versions and installation

  • CRAN The latest CRAN version may be found at https://CRAN.R-project.org/package=emmeans. Also at that site, formatted versions of this package's vignettes may be viewed.

  • Github To install the latest development version from Github, install the newest version (definitely 2.0 or higher) of the devtools package; then run

devtools::install_github("rvlenth/emmeans", dependencies = TRUE, build_opts = "")

### To install without vignettes (faster):
devtools::install_github("rvlenth/emmeans")

Note: If you are a Windows user, you should also first download and install the latest version of Rtools.

For the latest release notes on this development version, see the NEWS file