Input Data Sets
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
subgroupvariable. The subgroupvariable,
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
subgroupvariable.
If the i^{ th} subgroup contains
n_{i} items, there should be n_{i}
consecutive observations for which the value of the subgroupvariable
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)
 blockvariables
 symbolvariable
 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" .
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"
.
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 subgroupvariable
 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)
 blockvariables
 symbolvariable
 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" .
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 
subgroupvariable  values of the subgroupvariable 
_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
 blockvariables
 symbolvariable
 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" .
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.