Package 'lavinteract'

Simple slopes and interaction plots for fitted lavaan models

Description

Computes conditional (simple) slopes of a focal predictor across values of a moderator from a fitted lavaan model that includes their explicit product term. Plots predicted lines with Wald confidence ribbons, and print an APA-style test of the interaction for easy reporting and interpretation, plus a simple-slopes table.

Usage

lav_slopes(
  fit,
  outcome,
  pred,
  modx,
  interaction,
  data = NULL,
  modx.values = NULL,
  modx.labels = NULL,
  pred.range = NULL,
  conf.level = 0.95,
  x.label = NULL,
  y.label = NULL,
  legend.title = NULL,
  colors = NULL,
  line.size = 0.80,
  alpha = 0.20,
  table = TRUE,
  digits = 2,
  modx_n_unique_cutoff = 4L,
  return_data = FALSE
)

Arguments

fit	A fitted lavaan object that includes the product term (required).
outcome	Character. Name of the dependent variable in fit (required).
pred	Character. Name of the focal predictor whose simple slopes are probed (required).
modx	Character. Name of the moderator (required).
interaction	Character. Name of the product term in fit (e.g., "X_Z") (required).
data	data.frame. Raw data. If NULL, the function tries to pull data from fit via lavInspect.
modx.values	Numeric or character vector. Values or levels of the moderator at which to compute slopes; derived automatically when NULL.
modx.labels	Character vector. Legend/table labels for modx.values (default: the character form of modx.values).
pred.range	Numeric length-2. Range c(min, max) for the x-axis; uses observed range in data when available, else c(-2, 2).
conf.level	Numeric in (0,1). Confidence level for CIs and ribbons (default: 0.95).
x.label	Character. X-axis label (default: pred).
y.label	Character. Y-axis label (default: outcome).
legend.title	Character. Legend title; if NULL, the legend shows only levels (default: NULL).
colors	Character vector. Colors for lines and ribbons; named vector recommended with names matching modx.labels (default: Okabe–Ito palette).
line.size	Numeric > 0. Line width (default: 0.80).
alpha	Numeric in (0,1). Ribbon opacity (default 0.20).
table	Logical. Print APA-style interaction test and simple-slopes table (default: TRUE).
digits	Integer >= 0. Decimal digits in printed output (default: 2).
modx_n_unique_cutoff	Integer >= 1. Threshold for treating a numeric moderator as continuous and using mean ± SD (default: 4).
return_data	Logical. If TRUE, include the plotting data.frame in the returned list (default: FALSE).

Details

The model should include a main effect for the predictor, a main effect for the moderator, and their product term. The simple slope of the predictor at a given moderator value combines the predictor main effect with the interaction term. The moderator can be continuous or categorical. Standard errors use the delta method with the model covariance matrix of the estimates.

Value

A list with elements:

plot

ggplot object with lines and confidence ribbons.

slope_table

Data frame with moderator levels, simple slopes, SE, z, and CI.

plot_data

Only when return_data = TRUE: data used to build the plot.

Notes

Estimates are unstandardized; a standardized beta for the interaction is also reported for reference. Wald tests assume large-sample normality of estimates.

Examples

## Not run: 
library(lavaan)
# Fit a model with X, Z, and their product X_Z predicting Y
# model <- ' Y ~ X + Z + X_Z '
# fit <- sem(model, data = your_data)
# lav_slopes(fit, outcome = "Y", pred = "X", modx = "Z",
#            interaction = "X_Z", legend.title = "Moderator")

## End(Not run)

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Interaction Testing and Plotting for lavaan Fitted Objects

Description

Tools to test and visualize moderation in structural equation models fitted with lavaan using model estimates and their covariance without refitting. The framework accepts continuous or categorical moderators.

Details

The function is:

• lav_slopes: simple slopes and interaction plots from a fitted lavaan model.

Note

The development of this package was possible only thanks to the constant interaction (sic) with Dr. Cataldo Giuliano Gemmano (ORCID: 0000-0003-4519-8594), and particularly because of his sustained feedback and support.

Author(s)

Giuseppe Corbelli (<[email protected]>, or <[email protected]>)

See Also

Useful links:

• https://github.com/g-corbelli/lavinteract

• Report bugs at https://github.com/g-corbelli/lavinteract/issues

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