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 |
conf |
a numeric value used to compute control limits, specifying the number of standard deviations (if |
Methods available for estimating the process standard deviation:
Method | Description |
| UnWeighted AVErage of subgroup estimates |
based on subgroup Ranges |
|
| UnWeighted AVErage of subgroup estimates |
based on subgroup Standard Deviations |
|
| Minimum Variance Linear Unbiased Estimator |
computed as a weighted average of subgroups |
|
estimates based on subgroup Ranges |
|
| Minimum Variance Linear Unbiased Estimator |
computed as a weighted average of subgroup |
|
estimates based on subgroup Standard Deviations |
|
| Root-Mean-Square estimator computed as a weighted average of |
subgroup estimates based on subgroup Standard Deviations |
Method |
|
|
|
| default | default | not available |
| not available | default |
|
| not available |
||
| not available | ||
| 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.