plot_jn: Plot Interaction Effect Using the Johnson-Neyman Technique

In modsem: Latent Interaction (and Moderation) Analysis in Structural Equation Models (SEM)

Plot Interaction Effect Using the Johnson-Neyman Technique

Description

This function plots the simple slopes of an interaction effect across different values of a moderator variable using the Johnson-Neyman technique. It identifies regions where the effect of the predictor on the outcome is statistically significant.

Usage

plot_jn(
  x,
  z,
  y,
  xz = NULL,
  model,
  min_z = -3,
  max_z = 3,
  sig.level = 0.05,
  alpha = 0.2,
  detail = 1000,
  sd.line = 2,
  ...
)

Arguments

x	The name of the predictor variable (as a character string).
z	The name of the moderator variable (as a character string).
y	The name of the outcome variable (as a character string).
xz	The name of the interaction term. If not specified, it will be created using x and z.
model	A fitted model object of class modsem_da, modsem_mplus, modsem_pi, or lavaan.
min_z	The minimum value of the moderator variable z to be used in the plot (default is -3). It is relative to the mean of z.
max_z	The maximum value of the moderator variable z to be used in the plot (default is 3). It is relative to the mean of z.
sig.level	The significance level for the confidence intervals (default is 0.05).
alpha	alpha setting used in 'ggplot' (i.e., the opposite of opacity)
detail	The number of generated data points to use for the plot (default is 1000). You can increase this value for smoother plots.
sd.line	A thick black line showing +/- sd.line * sd(z). NOTE: This line will be truncated by min_z and max_z if the sd.line falls outside of [min_z, max_z].
...	Additional arguments (currently not used).

Details

The function calculates the simple slopes of the predictor variable x on the outcome variable y at different levels of the moderator variable z. It uses the Johnson-Neyman technique to identify the regions of z where the effect of x on y is statistically significant.

It extracts the necessary coefficients and variance-covariance information from the fitted model object. The function then computes the critical t-value and solves the quadratic equation derived from the t-statistic equation to find the Johnson-Neyman points.

The plot displays:

• The estimated simple slopes across the range of z.

• Confidence intervals around the slopes.

• Regions where the effect is significant (shaded areas).

• Vertical dashed lines indicating the Johnson-Neyman points.

• Text annotations providing the exact values of the Johnson-Neyman points.

Value

A ggplot object showing the interaction plot with regions of significance.

Examples

## Not run: 
library(modsem)

m1 <-  ' 
  visual  =~ x1 + x2 + x3 
  textual =~ x4 + x5 + x6
  speed   =~ x7 + x8 + x9

  visual ~ speed + textual + speed:textual
'

est <- modsem(m1, data = lavaan::HolzingerSwineford1939, method = "ca")
plot_jn(x = "speed", z = "textual", y = "visual", model = est, max_z = 6)

## End(Not run)

modsem documentation built on April 3, 2025, 7:51 p.m.