stats.xbar: Statistics used in computing and drawing a 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 = 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).

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.

Details

Methods available for estimating the process standard deviation: ll{ Method Description "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 }

llll{ 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.

References