f_qqnorm: Normal Q-Q Plot with Confidence Bands

In rfriend: Provides Batch Functions and Visualisation for Basic Statistical Procedures

Normal Q-Q Plot with Confidence Bands

Description

This function creates a normal Q-Q plot for a given numeric vector and adds confidence bands to visualize the variability of the quantiles.

Usage

f_qqnorm(
  x,
  main = NULL,
  ylab = NULL,
  conf_level = 0.95,
  col = NULL,
  pch = NULL,
  cex = NULL,
  save_png = FALSE,
  open_png = TRUE,
  save_as = NULL,
  save_in_wdir = FALSE,
  width = 8,
  height = 7,
  units = "in",
  res = 300,
  ...
)

Arguments

x	A numeric vector of data values.
main	Character string, specifying the title of the Q-Q plot. Default is "Normal Q-Q Plot with X% Confidence Band".
ylab	A character string specifying the y-axis label. Default name is "Quantiles of: data_name".
conf_level	Numeric, between 0 and 1. Confidence level for the confidence band. Default is 0.95 (95% confidence).
col	Numeric, optional parameter for color of point with default 'black'.
pch	Numeric, optional parameter shape of points default pch = 19.
cex	Numeric, optional parameter for graph cex with default cex = 0.6.
save_png	A logical value default FALSE, if TRUE a png file is saved under the name of the data or under the specified file name.
open_png	Logical. If TRUE, opens generated png files.
save_as	Character string specifying the output file path (without extension). If a full path is provided, output is saved to that location. If only a filename is given, the file is saved in tempdir(). If only a directory is specified (providing an existing directory with trailing slash), the file is named "data_name_QQplot.png" in that directory. Defaults to file.path(tempdir(), "data_name_QQplot.png").
save_in_wdir	Logical. If TRUE, saves the file in the working directory. Default is FALSE, this avoid unintended changes to the global environment. If save_as location is specified save_in_wdir is overwritten by save_as.
width	Numeric, png figure width default 8 inch.
height	Numeric, png figure height default 7 inch.
units	Character string, png figure units default "in" = inch, other options are: "px" = Pixels, "cm" centimeters, "mm" millimeters.
res	Numeric, png figure resolution default 300 dpi.
...	Additional graphical parameters to be passed to the qqnorm function.

Details

• The function calculates theoretical quantiles for a normal distribution and compares them with the sample quantiles of the input data.

• It also computes confidence intervals for the order statistics using the Blom approximation and displays these intervals as shaded bands on the plot.

• The reference line is fitted based on the first and third quartiles of both the sample data and theoretical quantiles.

• To increase resolution you can use png(...,res = 600) or the 'RStudio' chunck setting, e.g. dpi = 600.

Value

A Q-Q plot is created and the function returns this as a recordedplot.

Author(s)

Sander H. van Delden [e-mail]

Examples

# Generate random normal data
set.seed(123)
data <- rnorm(100)

# Create a Q-Q plot with confidence bands
f_qqnorm(data)

# Customize the plot with additional graphical parameters
f_qqnorm(data, conf_level = 0.99, pch = 16, col = "blue")

rfriend documentation built on July 7, 2026, 1:06 a.m.