Plots empirical quantiles of a variable, or of studentized residuals from a linear model, against theoretical quantiles of a comparison distribution.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27  qqPlot(x, ...)
qqp(...)
## Default S3 method:
qqPlot(x, distribution="norm", ...,
ylab=deparse(substitute(x)), xlab=paste(distribution, "quantiles"),
main=NULL, las=par("las"),
envelope=.95,
col=palette()[1], col.lines=palette()[2], lwd=2, pch=1, cex=par("cex"),
line=c("quartiles", "robust", "none"),
labels = if(!is.null(names(x))) names(x) else seq(along=x),
id.method = "y",
id.n =if(id.method[1]=="identify") Inf else 0,
id.cex=1, id.col=palette()[1], id.location="lr", grid=TRUE)
## S3 method for class 'lm'
qqPlot(x, xlab=paste(distribution, "Quantiles"),
ylab=paste("Studentized Residuals(", deparse(substitute(x)), ")",
sep=""), main=NULL,
distribution=c("t", "norm"), line=c("robust", "quartiles", "none"),
las=par("las"), simulate=TRUE, envelope=.95,
reps=100, col=palette()[1], col.lines=palette()[2], lwd=2,
pch=1, cex=par("cex"),
labels, id.method = "y",
id.n = if(id.method[1]=="identify") Inf else 0,
id.cex=1, id.col=palette()[1], id.location="lr", grid=TRUE, ...)

x 
vector of numeric values or 
distribution 
root name of comparison distribution – e.g., 
ylab 
label for vertical (empirical quantiles) axis. 
xlab 
label for horizontal (comparison quantiles) axis. 
main 
label for plot. 
envelope 
confidence level for pointwise confidence envelope, or

las 
if 
col 
color for points; the default is the first entry
in the current color palette (see 
col.lines 
color for lines; the default is the second entry in the current color palette. 
pch 
plotting character for points; default is 
cex 
factor for expanding the size of plotted symbols; the default is

labels 
vector of text strings to be used to identify points, defaults to

id.method 
point identification method. The default

id.n 
number of points labeled. If 
id.cex 
set size of the text for point labels; the default is 
id.col 
color for the point labels. 
id.location 
The default 
lwd 
line width; default is 
line 

simulate 
if 
reps 
integer; number of bootstrap replications for confidence envelope. 
... 
arguments such as 
grid 
If TRUE, the default, a lightgray background grid is put on the graph 
Draws theoretical quantilecomparison plots for variables and for studentized residuals from a linear model. A comparison line is drawn on the plot either through the quartiles of the two distributions, or by robust regression.
Any distribution for which quantile and
density functions exist in R (with prefixes q
and d
, respectively) may be used.
When plotting a vector, the confidence envelope is based on the SEs of the order statistics
of an independent random sample from the comparison distribution (see Fox, 2008).
Studentized residuals from linear models are plotted against the appropriate tdistribution with a pointwise
confidence envelope computed by default by a parametric bootstrap,
as described by Atkinson (1985).
The function qqp
is an abbreviation for qqPlot
.
These functions return the labels of identified points.
John Fox jfox@mcmaster.ca
Fox, J. (2008) Applied Regression Analysis and Generalized Linear Models, Second Edition. Sage.
Fox, J. and Weisberg, S. (2011) An R Companion to Applied Regression, Second Edition, Sage.
Atkinson, A. C. (1985) Plots, Transformations, and Regression. Oxford.
qqplot
, qqnorm
,
qqline
, showLabels
1 2 3 4 5 6 
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