Statistics used in computing and drawing a Shewhart np chart

These functions are used to compute statistics required by the np chart.

stats.np(data, sizes)
sd.np(data, sizes, ...)
limits.np(center, std.dev, sizes, nsigmas = NULL, conf = NULL)

Arguments

data

the observed data values

center

sample/group center statistic.

sizes

samples sizes.

std.dev

within group standard deviation.

nsigmas

a numeric value specifying the number of sigmas to use for computing control limits. It is ignored when the conf argument is provided.

conf

a numeric value in \((0,1)\) specifying the confidence level to use for computing control limits.

...

catches further ignored arguments.

Value

The function stats.np returns a list with components statistics and center. The function sd.np returns std.dev the standard deviation of the statistic charted. The function limits.np returns a matrix with lower and upper control limits.

References

Montgomery, D.C. (2013) Introduction to Statistical Quality Control, 7th ed. New York: John Wiley & Sons.

Wetherill, G.B. and Brown, D.W. (1991) Statistical Process Control. New York: Chapman & Hall.

Author

Luca Scrucca

See also

qcc