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qcc (version 1.2)

stats.xbar: Functions to plot Shewhart xbar chart

Description

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

Usage

stats.xbar(data, sizes)
sd.xbar(data, sizes, std.dev, equal.sd = TRUE)
limits.xbar(center, std.dev, sizes, conf)

Arguments

data
the observed data values
center
sample/group center statistic.
sizes
samples sizes. Optional
std.dev
within group standard deviation. Optional for sd.xbar function, required for limits.xbar
equal.sd
a logical indicating whether the standard deviation is constant for all samples/groups.
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.xbar returns a list with components statistics and center.

    The function sd.xbar returns std.dev the standard deviation of the statistic charted. This is based on results from Burr (1969).

    The function limits.xbar returns a matrix with lower and upper control limits.

References

Burr, I.W. (1969) Control charts for measurements with varying sample sizes. Journal of Quality Technology, 1(3), 163-167. Montgomery, D.C. (2000) Introduction to Statistical Quality Control, 4th ed. New York: John Wiley & Sons. Wetherill, G.B. and Brown, D.W. (1991) Statistical Process Control. New York: Chapman & Hall.

See Also

qcc