| stats.xbar {qcc} | R Documentation |
These functions are used to compute statistics required by the xbar chart.
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)
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). |
Methods available for estimating the process standard deviation:
| 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 |
| 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.
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.
Luca Scrucca luca@stat.unipg.it
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.