Quantile-quantile plot of model residuals

Usage

qq_plot(model, ...)

# S3 method for default
qq_plot(model, ...)

# S3 method for gam
qq_plot(
  model,
  method = c("uniform", "simulate", "normal", "direct"),
  type = c("deviance", "response", "pearson"),
  n_uniform = 10,
  n_simulate = 50,
  level = 0.9,
  ylab = NULL,
  xlab = NULL,
  title = NULL,
  subtitle = NULL,
  caption = NULL,
  ci_col = "black",
  ci_alpha = 0.2,
  point_col = "black",
  point_alpha = 1,
  line_col = "red",
  ...
)

# S3 method for glm
qq_plot(model, ...)

# S3 method for lm
qq_plot(model, ...)

Arguments

model: a fitted model. Currently only class "gam".
...: arguments passed ot other methods.
method: character; method used to generate theoretical quantiles. Note that method = "direct" is deprecated in favour of method = "uniform".
type: character; type of residuals to use. Only "deviance", "response", and "pearson" residuals are allowed.
n_uniform: numeric; number of times to randomize uniform quantiles in the direct computation method (method = "uniform").
n_simulate: numeric; number of data sets to simulate from the estimated model when using the simulation method (method = "simulate").
level: numeric; the coverage level for reference intervals. Must be strictly 0 < level < 1. Only used with method = "simulate".
ylab: character or expression; the label for the y axis. If not supplied, a suitable label will be generated.
xlab: character or expression; the label for the y axis. If not supplied, a suitable label will be generated.
title: character or expression; the title for the plot. See ggplot2::labs(). May be a vector, one per penalty.
subtitle: character or expression; the subtitle for the plot. See ggplot2::labs(). May be a vector, one per penalty.
caption: character or expression; the plot caption. See ggplot2::labs(). May be a vector, one per penalty.
ci_col: fill colour for the reference interval when method = "simulate".
ci_alpha: alpha transparency for the reference interval when method = "simulate".
point_col: colour of points on the QQ plot.
point_alpha: alpha transparency of points on the QQ plot.
line_col: colour used to draw the reference line.

Note

The wording used in mgcv::qq.gam() uses direct in reference to the simulated residuals method (method = "simulated"). To avoid confusion, method = "direct" is deprecated in favour of method = "uniform".

Examples

load_mgcv()
## simulate binomial data...
dat <- data_sim("eg1", n = 200, dist = "binary", scale = .33, seed = 0)
p <- binomial()$linkinv(dat$f) # binomial p
n <- sample(c(1, 3), 200, replace = TRUE) # binomial n
dat <- transform(dat, y = rbinom(n, n, p), n = n)
m <- gam(y / n ~ s(x0) + s(x1) + s(x2) + s(x3),
  family = binomial, data = dat, weights = n,
  method = "REML"
)

## Q-Q plot; default using direct randomization of uniform quantiles
qq_plot(m)


## Alternatively use simulate new data from the model, which
## allows construction of reference intervals for the Q-Q plot
qq_plot(m,
  method = "simulate", point_col = "steelblue",
  point_alpha = 0.4
)


## ... or use the usual normality assumption
qq_plot(m, method = "normal")