CCHART Statement: SHEWHART Procedure

You can read the number of nonconformities in subgroup samples from a DATA= data set specified in the PROC SHEWHART statement. Each process specified in the CCHART statement must be a SAS variable in the data set. This variable provides the number of nonconformities in subgroup samples indexed by the subgroup-variable. Typically (but not necessarily), the subgroup consists of a single inspection unit. The subgroup-variable, specified in the CCHART statement, must also be a SAS variable in the DATA= data set. Each observation in a DATA= data set must contain a value for each process and a value for the subgroup-variable. The data set must contain one observation per subgroup. Other variables that can be read from a DATA= data set include

By default, the SHEWHART procedure reads all of the observations in a DATA= data set. However, if the data set includes the variable _PHASE_, you can read selected groups of observations (referred to as phases) with the READPHASES= option (for an example, see Displaying Stratification in Phases.

For an example of a DATA= data set, see Creating c Charts from Defect Count Data.

You can read preestablished control limits (or parameters from which the control limits can be calculated) from a LIMITS= data set specified in the PROC SHEWHART statement. For example, the following statements read control limit information from the data set Conlims:

proc shewhart data=Info limits=Conlims;
   cchart Defects*Lot;
run;

The LIMITS= data set can be an OUTLIMITS= data set that was created in a previous run of the SHEWHART procedure. Such data sets always contain the variables required for a LIMITS= data set. The LIMITS= data set can also be created directly using a DATA step. When you create a LIMITS= data set, you must provide one of the following:

In addition, note the following:

For an example, see Reading Preestablished Control Limits.

You can read subgroup summary statistics from a HISTORY= data set specified in the PROC SHEWHART statement. This enables you to reuse OUTHISTORY= data sets that have been created in previous runs of the SHEWHART procedure or to create your own HISTORY= data set. A HISTORY= data set used with the CCHART statement must contain the following variables:

The names of the subgroup number of nonconformities per unit and subgroup sample size variables must be the process name concatenated with the special suffix characters U and N, respectively. For example, consider the following statements:

proc shewhart history=summary;
   cchart (flaws ndefects)*lot;
run;

The data set summary must include the variables lot, flawsU, flawsN, ndefctsU, and ndefctsN.

Note that if you specify a process name that contains 32 characters, the names of the summary variables must be formed from the first 16 characters and the last 15 characters of the process name, suffixed with the appropriate character. Other variables that can be read from a HISTORY= data set include

By default, the SHEWHART procedure reads all the observations in a HISTORY= data set. However, if the data set includes the variable _PHASE_, you can read selected groups of observations (referred to as phases) with the READPHASES= option (see Displaying Stratification in Phases for an example).

For an example of a HISTORY= data set, see Creating c Charts from Nonconformities per Unit.

You can read summary statistics and control limits from a TABLE= data set specified in the PROC SHEWHART statement. This enables you to reuse an OUTTABLE= data set created in a previous run of the SHEWHART procedure or to create your own TABLE= data set. Because the SHEWHART procedure simply displays the information in a TABLE= data set, you can use TABLE= data sets to create specialized control charts. Examples are provided in Specialized Control Charts: SHEWHART Procedure.

Table 18.16 lists the variables required in a TABLE= data set used with the CCHART statement.

Other variables that can be read from a TABLE= data set include

For an example of a TABLE= data set, see Saving Control Limits.