ppoints                 package:base                 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 generate 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.

See Also:

     `qqplot', `qqnorm'.

Examples:

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

