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Reference line at null effect for forest plots

Source: R/geom-forest-ref.R
geom_forest_ref.Rd

geom_forest_ref() draws a vertical reference line at the null effect value — typically 0 for difference measures (MD, SMD) or 1 for ratio measures (RR, OR, HR). The line indicates where no treatment effect exists.

Usage

geom_forest_ref(
  mapping = NULL,
  data = NULL,
  ...,
  xintercept = 0,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE
)

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

The data to be displayed in this layer. There are three options:

If NULL, the default, the data is inherited from the plot data as specified in the call to ggplot().

A data.frame, or other object, will override the plot data. All objects will be fortified to produce a data frame. See fortify() for which variables will be created.

A function will be called with a single argument, the plot data. The return value must be a data.frame, and will be used as the layer data. A function can be created from a formula (e.g. ~ head(.x, 10)).

...

Other arguments passed on to ggplot2::layer().

xintercept

X-axis intercept for the reference line. Default: 0 (null effect for difference measures).

na.rm

If FALSE (default), missing values are removed with a warning. If TRUE, missing values are silently removed.

show.legend

logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

Value

A ggplot2 layer.

Aesthetics

geom_forest_ref() understands the following aesthetics:

  • colour — line colour (default: "gray50")

  • linewidth — line width (default: 0.5)

  • linetype — line type (default: "dashed")

  • alpha — transparency (default: 0.8)

Examples

library(ggplot2)
df <- data.frame(
  study = c("Study 1", "Study 2"),
  estimate = c(0.5, 0.8),
  lower = c(0.2, 0.6),
  upper = c(0.8, 1.0),
  weight = c(1, 2)
)
ggplot(df, aes(y = study, x = estimate, xmin = lower,
               xmax = upper, weight = weight)) +
  geom_forest_ref(xintercept = 0) +
  geom_forest_ci()