Quality and Reliability Methods - SAS

Chapter 5 Shewhart Control Charts 79
Shewhart Control Charts for Variables
and the standard deviation for Median Moving Range charts is estimated by
Std Dev = MMR/d 4 (n)
where
X = the mean of the individual measurements
MR = the mean of the nonmissing moving ranges computed as (MR n +MR n+1 +...+MR N )/N
σ = the process standard deviation
k = the number of standard deviations
MMR = Center Line (Avg) for Median Moving Range chart
d 2 (n) = expected value of the range of n independent normally distributed variables with unit standard
deviation.
d 3 (n) = standard error of the range of n independent observations from a normal population with unit
standard deviation.
d 4 (n) = expected value of the range of a normally distributed sample of size n.
Presummarize Charts
If your data consist of repeated measurements of the same process unit, then you will want to combine these
into one measurement for the unit. Pre-summarizing is not recommended unless the data have repeated
measurements on each process or measurement unit.
Presummarize summarizes the process column into sample means and/or standard deviations, based either
on the sample size or sample label chosen. Then it charts the summarized data based on the options chosen
in the launch dialog. You can also append a capability analysis by checking the appropriate box in the
launch dialog.
Example: Presummarize Chart
For an example, using the Coating.jmp data table,
1. Choose the Analyze > Quality And Process > Control Chart > Presummarize command.
2. Choose Weight as the Process variable and Sample as the Sample Label.
3. In the dialog check both Individual on Group Means and Moving Range on Group Means. The
Sample Grouped by Sample Label button is automatically selected when you choose a Sample Label
variable.
4. Click OK.