The qqplotr package extends some ggplot2 functionalities by permitting the drawing of both quantile-quantile (Q-Q) and probability-probability (P-P) points, lines, and confidence bands. The functions of this package also allow a detrend adjustment of the plots, proposed by Thode (2002) to help reduce visual bias when assessing the results.

Installation

If you would like to install the development version of qqplotr, you may do so by using, for example, devtools:

# install.packages("devtools")
library(devtools)
devtools::install_github("aloy/qqplotr")

If, instead, you wish to install the stable CRAN version, then simply do:

install.packages("qqplotr")

Details

The functions of this package, implemeneted as Stats from ggplot2, are divided into two groups: (1) Q-Q and (2) P-P plots.

Both groups are composed of three functions: point, line, and band. Those Stats complement each other when drawn together, but they may also be plotted independently.

Below we will give an overview of all those Stats and, further in the document, we will present some usage examples.

Q-Q plot

• stat_qq_point This is a modified version of ggplot2::stat_qq with some parameters adjustments and a new option to detrend the points.
• stat_qq_line Draws a reference line based on the data quantiles, as in stats::qqline.
• stat_qq_band Draws confidence bands based on three methods: "pointwise", "boot", "ks", and "ts":
  • "pointwise" constructs simultaneous confidence bands based on the normal distribution;
  • "boot" creates pointwise confidence bands based on a parametric boostrap;
  • "ks" constructs simultaneous confidence bands based on an inversion of the Kolmogorov-Smirnov test;
  • "ts" constructs tail-sensitive confidence bands, as proposed by Aldor-Noiman et al. (2013).

In order to facilitate the visualization of multiple Q-Q band methods at the same time, the geom_qq_band Geom was also implemented. Its usage will be illustrated further below.

P-P plot

• stat_pp_point Plots cumulative probabilities versus probability points. The cumulative probability function is constructed with the sample data, and then evaluated at each probability point.
• stat_pp_line Draws a reference identity line (