Description Usage Arguments Details Value Author(s) References See Also
These functions are used to compute statistics required by the xbar chart.
1 2 3  stats.xbar(data, sizes)
sd.xbar(data, sizes, std.dev = c("UWAVER", "UWAVESD", "MVLUER", "MVLUESD", "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 
The following methods are available for estimating the process standard deviation:
"UWAVER"
UnWeighted AVErage of subgroup estimates based on subgroup Ranges
"UWAVESD"
UnWeighted AVErage of subgroup estimates based on subgroup Standard Deviations
"MVLUER"
Minimum Variance Linear Unbiased Estimator computed as a weighted average of subgroups estimates based on subgroup Ranges
"MVLUESD"
Minimum Variance Linear Unbiased Estimator computed as a weighted average of subgroup estimates based on subgroup Standard Deviations
"RMSDF"
RootMeanSquare 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" 

"UWAVER"  default  default  not available  
"UWAVESD"  not available  default  
"MVLUER"  not available  
"MVLUESD"  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
Burr, I.W. (1969) Control charts for measurements with varying sample sizes. Journal of Quality Technology, 1(3), 163167.
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.
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