Output Data Sets

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CCHART Statement

Output Data Sets

OUTLIMITS= Data Set

The OUTLIMITS= data set saves control limits and control limit parameters. The following variables can be saved:

Table 33.21: OUTLIMITS= Data Set

Variable	Description
_ALPHA_	probability ( $\alpha$ ) of exceeding limits
_C_	value of central line on c chart ( $n_{i}\bar{u}$ or n_iu₀)
_INDEX_	optional identifier for the control limits specified with the OUTINDEX= option
_LCLC_	lower control limit for number of nonconformities
_LIMITN_	sample size associated with the control limits
_SIGMAS_	multiple (k) of standard error of c_i
_SUBGRP_	subgroup-variable specified in the CCHART statement
_TYPE_	type (estimate or standard value) of _U_
_U_	average number of nonconformities per unit ( $\bar{u}$ or u₀)
_UCLC_	upper control limit for number of nonconformities
_VAR_	process specified in the CCHART statement

Notes:

If the control limits vary with subgroup sample size, the special missing value V is assigned to the variables _C_, _LCLC_, _UCLC_, and _LIMITN_.
If the limits are defined in terms of a multiple k of the standard error of c_i, the value of _ALPHA_ is computed as P{c_i<_ LCLC_} + P{c_i>_ UCLC_}. If control limits vary with subgroup sample size and are determined in terms of k, _ALPHA_ is assigned the special missing value V.
If the limits are probability limits, the value of _SIGMAS_ is computed as $(\_{UCLC}\_ - \_{C}\_)/\sqrt{\_{C}\_}$ . If probability limits vary with subgroup sample size, _SIGMAS_ is assigned the special missing value V.
Optional BY variables are saved in the OUTLIMITS= data set.

The OUTLIMITS= data set contains one observation for each process specified in the CCHART statement. For an example, see "Saving Control Limits" .

OUTHISTORY= Data Set

The OUTHISTORY= data set saves subgroup statistics. The following variables are saved:

the subgroup-variable
a subgroup sample size variable named by process suffixed with N
a subgroup number of nonconformities per unit variable named by process suffixed with U

Given a process name that contains eight characters, the procedure first shortens the name to its first four characters and its last three characters, and then it adds the suffix. For example, the procedure shortens the process NDEFECTS to NDEFCTS before adding the suffix.

Subgroup summary variables are created for each process specified in the CCHART statement. For example, consider the following statements:

   proc shewhart data=fabric;
      cchart (flaws ndefects)*lot / outhistory=summary;
   run;

The data set SUMMARY contains variables named LOT, FLAWSU, FLAWSN, NDEFCTSU, and NDEFCTSN. Additionally, the following variables, if specified, are included:

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

For an example that creates an OUTHISTORY= data set, see "Saving Nonconformities per Unit" . Note that an OUTHISTORY= data set created with the CCHART statement can be used as a HISTORY= data set by either the CCHART statement or the UCHART statement.

OUTTABLE= Data Set

The OUTTABLE= data set saves subgroup summary statistics, control limits, and related information. The following variables are saved:

Variable Description

_ALPHA_ probability ( $\alpha$ ) of exceeding control limits

_EXLIM_ control limit exceeded on c chart

_LCLC_ lower control limit for number of nonconformities

_LIMITN_ nominal sample size associated with the control limits

_SIGMAS_ multiple (k) of the standard error associated with control limits

subgroup values of the subgroup variable

_SUBC_ subgroup number of nonconformities

_SUBN_ subgroup sample size

_TESTS_ tests for special causes signaled on c chart

_UCLC_ upper control limit for number of nonconformities

_VAR_ process specified in the CCHART statement

In addition, the following variables, if specified, are included:

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

Notes:

Either the variable _ALPHA_ or the variable _SIGMAS_ is saved depending on how the control limits are defined (with the ALPHA= or SIGMAS= options, respectively, or with the corresponding variables in a LIMITS= data set).
The variable _TESTS_ is saved if you specify the TESTS= option. The k^th character of a value of _TESTS_ is k if Test k is positive at that subgroup. For example, if you request the first four tests (the ones appropriate for c charts) and Tests 2 and 4 are positive for a given subgroup, the value of _TESTS_ has a 2 for the second character, a 4 for the fourth character, and blanks for the other six characters.
The variables _VAR_, _EXLIM_, and _TESTS_ are character variables of length 8. The variable _PHASE_ is a character variable of length 16. All other variables are numeric.

For an example, see "Saving Control Limits" .

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