R: Interaction-style plots for estimated marginal means

emmip {emmeans} | R Documentation

## Interaction-style plots for estimated marginal means

### Description

Creates an interaction plot of EMMs based on a fitted model and a simple formula specification.

### Usage

    emmip(object, formula, ...)

    ## Default S3 method:
    emmip(object, formula, type, CIs = FALSE,
      engine = get_emm_option("graphics.engine"), pch = c(1, 2, 6, 7, 9, 10,
      15:20), lty = 1, col = NULL, plotit = TRUE, ...)

### Arguments

`object` | An object of class `emmGrid`, or a fitted model of a class supported by the emmeans package
`formula` | Formula of the form `trace.factors ~ x.factors | by.factors`. The EMMs are plotted against `x.factor` for each level of `trace.factors`. `by.factors` is optional, but if present, it determines separate panels. Each element of this formula may be a single factor in the model, or a combination of factors using the `*` operator.
`...` | Additional arguments passed to `emmeans` (when `object` is not already an `emmGrid` object), `ggplot`, or `xyplot`.
`type` | As in `predict.emmGrid`, this determines whether we want to inverse-transform the predictions (`type = "response"`) or not (any other choice). The default is `"link"`, unless the `"predict.type"` option is in force; see `emm_options`.
`CIs` | Logical value. If `TRUE`, confidence intervals are added to the plot (works only with `engine = "ggplot"`)
`engine` | Character value matching `"ggplot"` (default) or `"lattice"`. The graphics engine to be used to produce the plot. These require, respectively, the ggplot2 or lattice package to be installed.
`pch` | The plotting characters to use for each group (i.e., levels of `trace.factors`). They are recycled as needed.
`lty` | The line types to use for each group. Recycled as needed.
`col` | The colors to use for each group, recycled as needed. If not specified, the default trellis colors are used.
`plotit` | Logical value. If `TRUE`, the plot is displayed. Otherwise, one may use the `"lattice"` attribute of the returned object and print it, perhaps after additional manipulation.

### Value

If `plotit = FALSE`, a `data.frame` (actually, a `summary_emm` object) with the table of EMMs that would be plotted. The variables plotted are named `xvar` and `yvar`, and the trace factor is named `tvar`. This data frame has an added `"labs"` attribute containing the labels `xlab`, `ylab`, and `tlab` for these respective variables. The confidence limits are also included, renamed `LCL` and `UCL`.

If `plotit = TRUE`, the function returns an object of class `"ggplot"` or a `"trellis"`, depending on `engine`.

### Details

If `object` is a fitted model, `emmeans` is called with an appropriate specification to obtain estimated marginal means for each combination of the factors present in `formula` (in addition, any arguments in `...` that match `at`, `trend`, `cov.reduce`, or `fac.reduce` are passed to `emmeans`). Otherwise, if `object` is an `emmGrid` object, its first element is used, and it must contain one estimate for each combination of the factors present in `formula`.

### Note

Conceptually, this function is equivalent to `interaction.plot` where the summarization function is thought to return the EMMs.

### See Also

`emmeans`, `interaction.plot`

### Examples

    #--- Three-factor example
    noise.lm = lm(noise ~ size * type * side, data = auto.noise)

    # Separate interaction plots of size by type, for each side
    emmip(noise.lm, type ~ size | side)

    # One interaction plot, using combinations of size and side as the x factor
    emmip(noise.lm, type ~ side * size)

    # One interaction plot using combinations of type and side as the trace factor
    emmip(noise.lm, type * side ~ size)

    # Individual traces in panels
    emmip(noise.lm, ~ size | type * side)

[Package emmeans version 1.1.3 Index]