stats.xbar: Statistics used in computing and drawing a Shewhart xbar...

In qcc: Quality Control Charts

Description

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

Usage

stats.xbar(data, sizes)
sd.xbar(data, sizes, std.dev = c("UWAVE-R", "UWAVE-SD", "MVLUE-R", "MVLUE-SD", "RMSDF"))
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. See details.
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).

Details

The following methods are available for estimating the process standard deviation:

"UWAVE-R"

UnWeighted AVErage of subgroup estimates based on subgroup Ranges

"UWAVE-SD"

UnWeighted AVErage of subgroup estimates based on subgroup Standard Deviations

"MVLUE-R"

Minimum Variance Linear Unbiased Estimator computed as a weighted average of subgroups estimates based on subgroup Ranges

"MVLUE-SD"

Minimum Variance Linear Unbiased Estimator computed as a weighted average of subgroup estimates based on subgroup Standard Deviations

"RMSDF"

Root-Mean-Square estimator computed as a weighted average of subgroup estimates based on subgroup Standard Deviations

Depending on the chart, a method may be available or not, or set as the default according to the following table:

Method		"xbar"	"R"	"S"
"UWAVE-R"		default	default	not available
"UWAVE-SD"			not available	default
"MVLUE-R"				not available
"MVLUE-SD"			not available
"RMSDF"			not available

Detailed definitions of formulae implemented are available in the SAS/QC 9.2 User's Guide.

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.

Author(s)

Luca Scrucca

References

Burr, I.W. (1969) Control charts for measurements with varying sample sizes. Journal of Quality Technology, 1(3), 163-167.
Montgomery, D.C. (2005) Introduction to Statistical Quality Control, 5th ed. New York: John Wiley & Sons.
Wetherill, G.B. and Brown, D.W. (1991) Statistical Process Control. New York: Chapman & Hall.

See Also

qcc

qcc documentation built on May 2, 2019, 9:15 a.m.