ppoints {stats}R Documentation

Ordinates for Probability Plotting

Description

Generates the sequence of “probability” points (1:m - a)/(m + (1-a)-a) where m is either n, if length(n)==1, or length(n).

Usage

ppoints(n, a = ifelse(n <= 10, 3/8, 1/2))

Arguments

n either the number of points generated or a vector of observations.
a the offset fraction to be used; typically in (0,1).

Details

If 0 < a < 1, the resulting values are within (0,1) (excluding boundaries). In any case, the resulting sequence is symmetric in [0,1], i.e., p + rev(p) == 1.

ppoints() is used in qqplot and qqnorm to generate the set of probabilities at which to evaluate the inverse distribution.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

qqplot, qqnorm.

Examples

ppoints(4) # the same as  ppoints(1:4)
ppoints(10)
ppoints(10, a=1/2)

[Package stats version 2.1.0 Index]