plot_moderation_curve: Plot moderation curves with Johnson-Neyman highlights

Description

plot_moderation_curve() visualises how an indirect effect (theta_curve) or a path coefficient (path_curve) varies along a continuous moderator W.

The routine

extracts the requested record (path_name) from result$moderation, preferring theta_curve when it is available in both curves;
draws the conditional effect (Estimate) against the raw moderator grid (W_raw);
overlays the Monte-Carlo confidence band (CI.LL, CI.UL) and finds every Johnson–Neyman segment whose 95 % CI excludes zero (CI.LL * CI.UL > 0);
shades these significant regions and annotates each with its start / end percentiles (for example, "sig 12.5%-38.3%").

Visual elements

Red ribbon – overall 95 % confidence band (ns_fill);
Green ribbon – significant Johnson–Neyman intervals (sig_fill);
Solid line – point estimate;
Dashed h-line – zero reference;
Dashed v-lines – J–N bounds.

Usage

plot_moderation_curve(
  result,
  path_name,
  title = NULL,
  x_label = "Moderator (W)",
  y_label = "Estimate",
  ns_fill = "#FEE0D2",
  sig_fill = "#C7E9C0",
  alpha_ci = 0.35,
  alpha_sig = 0.35,
  base_size = 14
)

Value

A ggplot object (add layers or save with ggsave()).

Arguments

result: A wsMed() result that contains a $moderation element.
path_name: Exact name of the path to plot (e.g. "indirect_1_2" or "b_1_2"). When the name exists in both curves, theta_curve is used.
title: Optional plot title (default sprintf("Effect Curve: (%s)", path_name)).
x_label, y_label: Axis labels. Defaults are "Moderator (W)" and "Estimate".
ns_fill, sig_fill: Fill colours for the confidence band and the significant regions.
alpha_ci, alpha_sig: Alpha values for the two ribbons.
base_size: Base font size passed to ggplot2::theme_minimal().