Plot an Effect Against a Moderator

It plots an effect, direct or indirect, against a moderator, with confidence band if available.

Usage

plot_effect_vs_w(
  object,
  w = NULL,
  w_label = NULL,
  effect_label = NULL,
  add_zero_line = TRUE,
  always_draw_zero_line = FALSE,
  line_linewidth = 1,
  line_color = "blue",
  shade_the_band = TRUE,
  draw_the_intervals = TRUE,
  band_fill_color = "lightgrey",
  band_alpha = 0.5,
  intervals_color = "black",
  intervals_linetype = "longdash",
  intervals_linewidth = 1,
  zero_line_color = "grey",
  zero_line_linewidth = 1,
  zero_line_linetype = "solid",
  line_args = list(),
  band_args = list(),
  intervals_args = list(),
  zero_line_args = list()
)

Arguments

object

The output of cond_indirect_effects().

w

The name of the moderator. Must be present in object. If NULL, the default, and object has only one moderator, then it will be set to that moderator. Because this function currently only supports a path with only one moderator, this argument can be left as NULL for now.

w_label

The label of the horizontal axis. If NULL, the default, it will be paste0("Moderator: ", w).

effect_label

The label of the vertical axis. If NULL, the default, it will be generated from the path.

add_zero_line

Whether a horizontal line at zero will be drawn. Default is TRUE.

always_draw_zero_line

If FALSE, the default, then the line at zero, if requested will be drawn only if zero is within the range of the plot. If TRUE, then the line at zero will always be drawn.

line_linewidth

The width of the line of the effect for each level of the moderator, to be used by ggplot2::geom_line(). Default is 1. Always overrides the value of line_args.

line_color

The color of the line of the effect for each level of the moderator, to be used by ggplot2::geom_line(). Default is "blue". Always overrides the value of line_args.

shade_the_band

If TRUE, the default, a confidence band will be drawn as a region along the line if confidence intervals can be retrieved from object.

draw_the_intervals

If TRUE, the default, two lines will be drawn for the confidence intervals along the line if they can be retrieved from object.

band_fill_color

The color of of the confidence band, to be used by ggplot2::geom_ribbon(). Default is "lightgrey". Always overrides the value of band_args.

band_alpha

A number from 0 to 1 for the level of transparency of the confidence band, to be used by ggplot2::geom_ribbon(). Default is .50. Always overrides the value of band_args.

intervals_color

The color of the lines of the confidence intervals, to be used by ggplot2::geom_line(). Default is "black". Always overrides the value of intervals_args.

intervals_linetype

The line type of the lines of the confidence intervals, to be used by ggplot2::geom_line(). Default is "longdash". Always overrides the value of intervals_args.

intervals_linewidth

The line width of the lines of the confidence intervals, to be used by ggplot2::geom_line(). Default is 1. Always overrides the value of intervals_args.

zero_line_color

The color of the line at zero, to be used by ggplot2::geom_line(). Default is "grey". Always overrides the value of zero_line_args.

zero_line_linewidth

The line width of the line at zero, to be used by ggplot2::geom_line(). Default is 1. Always overrides the value of zero_line_args.

zero_line_linetype

The line type of the line at zero, to be used by ggplot2::geom_line(). Default is "solid". Always overrides the value of zero_line_args.

line_args

A named list of additional arguments to be passed to ggplot2::geom_line() for the line of the effect against moderator. Default is list().

band_args

A named list of additional arguments to be passed to ggplot2::geom_ribbon() for the confidence band. Default is list().

intervals_args

A named list of additional arguments to be passed to ggplot2::geom_line() for the lines of confidence intervals. Default is list().

zero_line_args

A named list of additional arguments to be passed to ggplot2::geom_line() for the line at zero. Default is list().

Value

A ggplot2 graph. Plotted if not assigned to a name. It can be further modified like a usual ggplot2 graph.

Details

It receives an output of cond_indirect_effects() and plot the effect against the moderator. The effect can be an indirect effect or a direct effect.

It uses the levels of the moderator stored in the output of cond_indirect_effects(). Therefore, the desired levels of the moderator to be plotted needs to be specified when calling cond_indirect_effects(), as illustrated in the example.

Currently, this function only supports a path with exactly one moderator, and the moderator is a numeric variable.

See also

cond_indirect_effects()

Examples

dat <- data_med_mod_a
lm_m <- lm(m ~ x*w + c1 + c2, dat)
lm_y <- lm(y ~ m + x + c1 + c2, dat)
fit_lm <- lm2list(lm_m, lm_y)
# Set R to a large value in real research.
boot_out_lm <- do_boot(fit_lm,
                       R = 50,
                       seed = 54532,
                       parallel = FALSE,
                       progress = FALSE)

# Compute the conditional indirect effects
# from 2 SD below mean to 2 SD above mean of the moderator,
# by setting sd_from_mean of cond_indirect_effects().
# Set length.out to a larger number for a smooth graph.
out_lm <- cond_indirect_effects(wlevels = "w",
                                x = "x",
                                y = "y",
                                m = "m",
                                fit = fit_lm,
                                sd_from_mean = seq(-2, 2, length.out = 10),
                                boot_ci = TRUE,
                                boot_out = boot_out_lm)
p <- plot_effect_vs_w(out_lm)
p

# The output is a ggplot2 graph and so can be further customized
library(ggplot2)
# Add the line for the mean of w, the moderator
p2 <- p + geom_vline(xintercept = mean(dat$w),
                     color = "red")
p2