Input Data Sets

XCHART Statement

Input Data Sets

DATA= Data Set

You can read raw data (process measurements) from a DATA= data set specified in the PROC SHEWHART statement. Each process specified in the XCHART statement must be a SAS variable in the DATA= data set. This variable provides measurements that must be grouped into subgroup samples indexed by the subgroup-variable. The subgroup-variable, which is specified in the XCHART 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. 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 subgroup contains five items and there are 30 subgroup samples, the DATA= data set should contain 150 observations.

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

_PHASE_ (if the READPHASES= option is specified)
block-variables
symbol-variable
BY variables
ID variables

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 Charts for Means from Raw Data" .

LIMITS= Data Set

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;
      xchart weight*batch;
   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; see Table 42.23. 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:

the variables _LCLX_, _MEAN_, and _UCLX_, which specify the control limits directly
the variables _MEAN_ and _STDDEV_, which are used to calculate the control limits according to the equations in Table 42.22

In addition, note the following:

The variables _VAR_ and _SUBGRP_ are required. These must be character variables of length 8.
The variable _INDEX_ is required if you specify the READINDEX= option; this must be a character variable of length 16.
The variables _LIMITN_, _SIGMAS_ (or _ALPHA_), and _TYPE_ are optional, but they are recommended to maintain a complete set of control limit information. The variable _TYPE_ must be a character variable of length 8; valid values are ESTIMATE, STANDARD, STDMU, and STDSIGMA.
BY variables are required if specified with a BY statement.

For an example, see "Reading Preestablished Control Limits" .

HISTORY= Data Set

You can read subgroup summary statistics from a HISTORY= data set specified in the PROC SHEWHART statement. This allows you to reuse OUTHISTORY= data sets that have been created in previous runs of the SHEWHART, CUSUM, or MACONTROL procedures or to read output data sets created with SAS summarization procedures, such as PROC MEANS.

A HISTORY= data set used with the XCHART statement must contain the following:

the subgroup-variable
a subgroup mean variable for each process
a subgroup sample size variable for each process
either a subgroup range variable or subgroup standard deviation variable for each process

If you specify the STDDEVIATIONS option, the subgroup standard deviation variable must be included; otherwise, the subgroup range variable must be included.

The names of the subgroup mean, subgroup range or subgroup standard deviation, and subgroup sample size variables must be the process name concatenated with the suffix characters X, R or S, and N, respectively.

For example, consider the following statements:

   proc shewhart history=summary;
      xchart (weight yldstren)*batch;
   run;

The data set SUMMARY must include the variables BATCH, WEIGHTX, WEIGHTR, WEIGHTN, YLDSRENX, YLDSRENR, and YLDSRENN. If the STDDEVIATIONS option were specified in the preceding XCHART statement, it would be necessary for SUMMARY to include the variables BATCH, WEIGHTX, WEIGHTS, WEIGHTN, YLDSRENX, YLDSRENS, and YLDSRENN.

Note that if you specify a process name that contains eight characters, the names of the summary variables must be formed from the first four characters and the last three characters of the process name, suffixed with the appropriate character.

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

_PHASE_ (if the READPHASES= option is specified)
block-variables
symbol-variable
BY variables
ID variables

By default, the SHEWHART procedure reads all of 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) by specifying the READPHASES= option (see "Displaying Stratification in Phases" for an example).

For an example of a HISTORY= data set, see "Creating Charts for Means from Subgroup Summary Data" .

TABLE= Data Set

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. 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 Chapter 49, "Specialized Control Charts."

The following table lists the variables required in a TABLE= data set used with the XCHART statement:

Table 42.25: Variables Required in a TABLE= Data Set

Variable	Description
_LCLX_	lower control limit for mean
_LIMITN_	nominal sample size associated with the control limits
_MEAN_	process mean
subgroup-variable	values of the subgroup-variable
_SUBN_	subgroup sample size
_SUBX_	subgroup mean
_UCLX_	upper control limit for mean

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

block-variables
symbol-variable
BY variables
ID variables
_PHASE_ (if the READPHASES= option is specified). This variable must be a character variable of length 16.
_TESTS_ (if the TESTS= option is specified). This variable is used to flag tests for special causes and must be a character variable of length 8.
_VAR_. This variable is required if more than one process is specified or if the data set contains information for more than one process. This variable must be a character variable of length 8.

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

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