Output Data Sets

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NPCHART 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 37.21: OUTLIMITS= Data Set

Variable	Description
_ALPHA_	probability ( $\alpha$ ) of exceeding limits
_INDEX_	optional identifier for the control limits specified with the OUTINDEX= option
_LCLNP_	lower control limit for number of nonconforming items
_LIMITN_	sample size associated with the control limits
_NP_	average number of nonconforming items ( $n_i\bar{p}$ or n_ip₀)
_P_	average proportion of nonconforming items ( $\bar{p}$ or p₀)
_SIGMAS_	multiple (k) of standard error of X_i
_SUBGRP_	subgroup-variable specified in the NPCHART statement
_TYPE_	type (standard or estimate) of _NP_
_UCLNP_	upper control limit for number of nonconforming items
_VAR_	process specified in the NPCHART statement

Notes:

If the control limits vary with subgroup sample size, the special missing value V is assigned to the variables _LIMITN_, _LCLNP_, _UCLNP_, _NP_, and _SIGMAS_.
If the limits are defined in terms of a multiple k of the standard error of X_i, the value of _ALPHA_ is computed as $\alpha = P\{X_i \lt {\_LCLNP\_}\} + P\{X_i \gt {\_UCLNP\_}\}$ , using the incomplete beta function.
If the limits are probability limits, the value of _SIGMAS_ is computed as $k=({\_UCLNP\_} - {\_NP\_})/ \sqrt{{\_NP\_}(1-{\_NP\_}) /{\_LIMITN\_}}$ .If _LIMITN_ has the special missing value V, this value is assigned to _SIGMAS_.
Optional BY variables are saved in the OUTLIMITS= data set.

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

OUTHISTORY= Data Set

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

the subgroup-variable
the subgroup proportion of nonconforming items variable named by the process suffixed with P
a subgroup sample size variable named by the process suffixed with N

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 REJECTED to REJETED before adding the suffix.

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

   proc shewhart data=input;
      npchart (rework rejected)*batch / outhistory=summary
                                        subgroupn =30;
   run;

The data set SUMMARY contains variables named BATCH, REWORKP, REWORKN, REJETEDP, and REJETEDN.

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 of an OUTHISTORY= data set, see "Saving Proportions of Nonconforming Items" .

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 np chart

_LCLNP_ lower control limit for number of nonconforming items

_LIMITN_ nominal sample size associated with the control limits

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

subgroup values of the subgroup variable

_SUBNP_ subgroup number of nonconforming items

_SUBN_ subgroup sample size

_TESTS_ tests for special causes signaled on np chart

_UCLNP_ upper control limit for number of nonconforming items

_VAR_ process specified in the NPCHART 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 tests appropriate for np 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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