You can read raw data (process measurements) from a DATA= data set specified in the PROC SHEWHART statement. Each process specified in the XRCHART 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 XRCHART 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 ith subgroup contains items, there should be consecutive observations for which the value of the subgroup variable is the index of the ith 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 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 (for an example, see Displaying Stratification in Phases).
For an example of a DATA= data set, see Creating Charts for Means and Ranges 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
:^{[85]}
proc shewhart data=Info limits=Conlims; xrchart 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. The LIMITS= data set can also be created directly by using a DATA step. When you create a LIMITS= data set, you must provide one of the following:
the variables _LCLX_
, _MEAN_
, _UCLX_
, _LCLR_
, _R_
, and _UCLR_
, 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 17.72
In addition, note the following:
The variables _VAR_
and _SUBGRP_
are required. These must be character variables whose lengths are no greater than 32.
The variable _INDEX_
is required if you specify the READINDEX= option; this must be a character variable whose length is no greater than 48.
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 enables you to reuse OUTHISTORY= data sets that have been created in previous runs of the SHEWHART, CUSUM, or MACONTROL procedure or to read output data sets created with SAS summarization procedures, such as the MEANS procedure.
A HISTORY= data set used with the XRCHART statement must contain the following variables:
the subgroupvariable
a subgroup mean variable for each process
a subgroup range variable for each process
a subgroup sample size variable for each process
The names of the subgroup mean, subgroup range, and subgroup sample size variables must be the process name concatenated with the special suffix characters X, R, and N, respectively.
For example, consider the following statements:
proc shewhart history=Summary; xrchart (Weight Yieldstrength)*Batch; run;
The data set Summary
must include the variables Batch
, WeightX
, WeightR
, WeightN
, YieldstrengthX
, YieldstrengthR
, and YieldstrengthN
.
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
_PHASE_
(if the READPHASES= option is specified)
blockvariables
symbolvariable
BY variables
ID variables
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) 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 and Ranges from 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 or to read data sets created by other SAS procedures. Because the SHEWHART procedure simply displays the information read from 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 17.76 lists the variables required in a TABLE= data set used with the XRCHART statement.
Table 17.76: Variables Required in a TABLE= Data Set
Variable 
Description 


lower control limit for range 

lower control limit for mean 

nominal sample size associated with the control limits 

process mean 

average range 
subgroupvariable 
values of the subgroupvariable 

subgroup sample size 

subgroup range 

subgroup mean 

upper control limit for range 

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 whose length is no greater than 48.
_TESTS_
(if the TESTS= option is specified). This variable is used to flag tests for special causes for subgroup means and must be
a character variable of length 8.
_TESTS2_
(if the TESTS2= option is specified). This variable is used to flag tests for special causes for subgroup ranges 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 whose length is no greater than 32.
For an example of a TABLE= data set, see Saving Control Limits.