plot_prism: PRISM plot (Partial Residual Intervenor Scatterplot Matrix)

In antedep: Antedependence Models for Longitudinal Data

PRISM plot (Partial Residual Intervenor Scatterplot Matrix)

Description

Creates a matrix of scatterplots for diagnosing antedependence structure. The upper triangle shows ordinary scatterplots of Y[i] vs Y[j]. The lower triangle shows PRISM plots: residuals from regressing Y[i] and Y[j] on the intervenor variables ⁠Y[i+1], ..., Y[j-1]⁠.

Usage

plot_prism(
  y,
  time_labels = NULL,
  pch = 20,
  cex = 0.6,
  col_upper = "steelblue",
  col_lower = "firebrick",
  main = "PRISM Diagnostic Plot"
)

Arguments

y	Numeric matrix with n_subjects rows and n_time columns.
time_labels	Optional character vector of time point labels. Default uses column names or "T1", "T2", etc.
pch	Point character for scatterplots. Default 20 (filled circle).
cex	Point size. Default 0.6.
col_upper	Color for upper triangle plots. Default "steelblue".
col_lower	Color for lower triangle (PRISM) plots. Default "firebrick".
main	Overall title. Default "PRISM Diagnostic Plot".

Details

Under an antedependence model of order p, the partial correlation between Y[i] and Y[j] given the intervenors should be zero when |i-j| > p. This means PRISM plots in the lower triangle should show no association for lags greater than p.

Interpretation:

• Upper triangle: Shows marginal associations between time points

• Lower triangle (PRISM): Shows conditional associations after removing effects of intervenor variables

• If AD(1) holds: Only the first sub-diagonal of lower triangle should show association

• If AD(2) holds: First two sub-diagonals should show association

Value

Invisibly returns NULL. Called for side effect (plotting).

References

Zimmerman, D. L. and Nunez-Anton, V. (2009). Antedependence Models for Longitudinal Data. CRC Press. Chapter 2.

See Also

partial_corr for numerical partial correlations

Examples

data("bolus_inad")
plot_prism(bolus_inad$y)

# With custom labels
plot_prism(bolus_inad$y, time_labels = paste0("Hour ", seq(0, 44, by = 4)))

antedep documentation built on April 25, 2026, 1:06 a.m.