PPD distributions

Plot posterior or prior predictive distributions. Each of these functions makes the same plot as the corresponding ppc_ function but without plotting any observed data y. The Plot Descriptions section at PPC-distributions has details on the individual plots.

ppd_data(ypred, group = NULL)

ppd_dens_overlay(
  ypred,
  ...,
  size = 0.25,
  alpha = 0.7,
  trim = FALSE,
  bw = "nrd0",
  adjust = 1,
  kernel = "gaussian",
  n_dens = 1024
)

ppd_ecdf_overlay(
  ypred,
  ...,
  discrete = FALSE,
  pad = TRUE,
  size = 0.25,
  alpha = 0.7
)

ppd_dens(ypred, ..., trim = FALSE, size = 0.5, alpha = 1)

ppd_hist(ypred, ..., binwidth = NULL, bins = NULL, breaks = NULL, freq = TRUE)

ppd_freqpoly(
  ypred,
  ...,
  binwidth = NULL,
  bins = NULL,
  freq = TRUE,
  size = 0.5,
  alpha = 1
)

ppd_freqpoly_grouped(
  ypred,
  group,
  ...,
  binwidth = NULL,
  bins = NULL,
  freq = TRUE,
  size = 0.5,
  alpha = 1
)

ppd_boxplot(ypred, ..., notch = TRUE, size = 0.5, alpha = 1)

Arguments

ypred

An S by N matrix of draws from the posterior (or prior) predictive distribution. The number of rows, S, is the size of the posterior (or prior) sample used to generate ypred. The number of columns, N, is the number of predicted observations.

group

A grouping variable of the same length as y. Will be coerced to factor if not already a factor. Each value in group is interpreted as the group level pertaining to the corresponding observation.

...

Currently unused.

size, alpha

Passed to the appropriate geom to control the appearance of the predictive distributions.

trim

A logical scalar passed to ggplot2::geom_density().

bw, adjust, kernel, n_dens

Optional arguments passed to stats::density() to override default kernel density estimation parameters. n_dens defaults to 1024.

discrete

For ppc_ecdf_overlay(), should the data be treated as discrete? The default is FALSE, in which case geom="line" is passed to ggplot2::stat_ecdf(). If discrete is set to TRUE then geom="step" is used.

pad

A logical scalar passed to ggplot2::stat_ecdf().

binwidth

Passed to ggplot2::geom_histogram() to override the default binwidth.

bins

Passed to ggplot2::geom_histogram() to override the default binwidth.

breaks

Passed to ggplot2::geom_histogram() as an alternative to binwidth.

freq

For histograms, freq=TRUE (the default) puts count on the y-axis. Setting freq=FALSE puts density on the y-axis. (For many plots the y-axis text is off by default. To view the count or density labels on the y-axis see the yaxis_text() convenience function.)

notch

For the box plot, a logical scalar passed to ggplot2::geom_boxplot(). Note: unlike geom_boxplot(), the default is notch=TRUE.

Value

The plotting functions return a ggplot object that can be further customized using the ggplot2 package. The functions with suffix _data() return the data that would have been drawn by the plotting function.

Details

For Binomial data, the plots may be more useful if the input contains the "success" proportions (not discrete "success" or "failure" counts).

See also

Other PPDs: PPD-intervals, PPD-overview, PPD-test-statistics

Examples

# difference between ppd_dens_overlay() and ppc_dens_overlay()
color_scheme_set("brightblue")
preds <- example_yrep_draws()
ppd_dens_overlay(ypred = preds[1:50, ])

ppc_dens_overlay(y = example_y_data(), yrep = preds[1:50, ])