iMediate (version 0.5.5)

figure.relative.power: Contour Plot of Relative Power: Mediated Effect versus Total Effect, Mediated Effect versus Direct Effect

Description

Contour plot of relative power of mediated effect versus total effect in the absence of direct effect and relative power of mediated effect versus direct effect when \(ab=c'\).

Usage

figure.relative.power(comparison = "mediated2main", n = 100,
  sig.level = 0.05, grid.size = 0.01)

Arguments

comparison

a character string specifying the relative power to be plotted. One of "mediated2main" (default) and "mediated2direct". "mediated2main" requests the log of power ratio for the mediated effect versus the main effect assuming there is no direct effect (\(c'=0\)). "mediated2direct" requests the log of power ratio for the mediated effect versus the direct effect assuming \(ab=c'\)

n

sample size

sig.level

significance level used for the test of the mediated effect

grid.size

grid size for \(a^2\) and \(b^2\)

Value

A plot generated using package plotly

Details

Basic three-factor mediation model is assumed. Coefficients are standardized such that the variances of treatment, mediator, and outcome are equal to 1. Note that the y-axis is \(a^2\) and the x-axis is \(b^2\). The default axes labels from R function plot_ly are switched in order to make them correct.

References

Wang, K. (2018) Understanding power anomalies in mediation analysis. Psychometrika 83 (2), 387-406.

Examples

# NOT RUN {
## figure.relative.power()                                # Figure 2 of Wang (2018)
## figure.relative.power(comparison="mediated2direct")    # Figure 3 of Wang (2018)

# }