Influence Index Plot

Plots the total local-influence measure \(C_{I_t}\) for each observation under case-weight perturbation, as used in the companion article (Ospina et al., 2026, Figure 2). A horizontal reference line at \(2 \bar{C}_I\) flags potentially influential observations.

Usage

plot_influence(
  x,
  threshold = 2,
  col.bar = "#2c7bb6",
  col.line = "#d7191c",
  label = TRUE,
  main = "Local influence -- case-weight perturbation",
  xlab = "Observation index",
  ylab = expression(C[It]),
  ...
)

Arguments

x

A "simplexfit" object from simplex_fit, or a list containing at least $Cei (influence vector of length \(n\)) as returned by simplex_diag.

threshold

Numeric scalar; multiplier for the mean of \(C_{I_t}\) used to draw the reference line. Default 2.

col.bar

Colour for the bars. Default "#2c7bb6".

col.line

Colour for the reference line. Default "#d7191c".

label

Logical; whether to label bars above the threshold with their index. Default TRUE.

main, xlab, ylab

Plot title and axis labels.

...

Additional arguments passed to plot.

Value

Invisibly returns the numeric vector \(C_{I_t}\).

See also

simplex_diag, simplex_fit, plot.simplexfit

Examples

data(ammonia)
X <- cbind(1, ammonia$corr_ar, ammonia$temp_agua,
           ammonia$corr_ar * ammonia$temp_agua)
Z <- cbind(1, ammonia$temp_agua,
           ammonia$corr_ar * ammonia$temp_agua)
fit <- simplex_fit(ammonia$perda, X, Z)
dg  <- simplex_diag(fit)
plot_influence(dg)