TeachingDemos (version 1.2)

limits.g: Functions to plot Shewhart g chart

Description

These functions are used to compute statistics required by the g chart (geometric distribution) for use with the qcc package.

Usage

stats.g(data, sizes)
sd.g(data, sizes)
limits.g(center, std.dev, sizes, conf)

Arguments

data

the observed data values

center

sample center statistic

sizes

sample sizes (not used)

std.dev

standard deviation of geometric distribution

conf

a numeric value used to compute control limits, specifying the number of standard deviations (if 'conf' > 1) or the confidence level (if 0 < 'conf' < 1).

Value

• The function 'stats.g' returns a list with components 'statistics' and 'center'. The function 'sd.g' returns 'std.dev' the standard deviation (sqrt(1-p)/p). The function 'limits.g' returns a matrix with lower and upper control limits.

Details

These functions work with the qcc package and may someday be moved into the qcc package. The g chart plots the number of non-events between events. np charts do not work well when the probability of an event is rare (see example below). Instead of plotting the number of events, the g chart plots the number of non-events between events.

See Also

qcc

Examples

if(require(qcc)){
  tmp <- rbinom(1000, 1, 0.01)
  tmp2 <- diff(which(c(1,tmp)==1))-1
  qcc(tmp,'np',1)
  qcc(tmp2, "g")
}