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XCHART Statement |
Each observation in a DATA= data set should contain a raw measurement for each process and a value for the subgroup variable. If the i^{ th} subgroup contains n_{i} items, there should be n_{i} consecutive observations for which the value of the subgroup variable is the index of the i^{ th} subgroup. For example, if each of 30 subgroup samples contains five items, the DATA= data set should contain 150 observations.
By default, the CUSUM procedure reads all of the observations in a DATA= data set. However, if the DATA= data set includes the variable _PHASE_, you can read selected groups of observations (referred to as phases) by specifying the READPHASES= option in the XCHART statement.
For an example of a DATA= data set, see "Creating a V-Mask Cusum Chart from Raw Data" .
The LIMITS= data set can be an OUTLIMITS= data set that was created in a previous run of the CUSUM procedure. Such data sets always contain the variables required for a LIMITS= data set; consequently, this is the easiest way to construct a LIMITS= data set.
A LIMITS= data set can also be created directly using a DATA step.
The variables required for the data set depend on the
type of cusum scheme and how the scheme is specified.
The following restrictions apply:
Variable names in a LIMITS= data set are predefined; the procedure reads only variables with these predefined names. With the exception of BY variables, all names start and end with an underscore. In addition, note the following:
For an example of reading control limit information from a LIMITS= data set, see "Reading Cusum Scheme Parameters" .
The names of the subgroup mean, subgroup standard deviation, and subgroup sample size variables must be the process concatenated with the special suffix characters X, S, and N respectively.
For example, consider the following statements:
proc cusum history=steel limits=stlparm; xchart (weight yldstren)*batch; run;
The data set STEEL must contain the variables BATCH, WEIGHTX, WEIGHTS, WEIGHTN, YLDSRENX, YLDSRENS, and YLDSRENN.
Note that if you specify a process that is eight characters long, the procedure uses a prefix formed from the first four characters and the last three characters of the process.
Other variables that can be read from a HISTORY= data set include
By default, the CUSUM procedure reads all of the observations in a HISTORY= data set. However, if the HISTORY= data set includes the variable _PHASE_, you can read selected groups of observations (referred to as phases) by specifying the READPHASES= option.
For an example of reading summary information from a HISTORY= data set, see "Creating a V-Mask Cusum Chart from Subgroup Summary Data" .
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