Chapter Contents 
Previous 
Next 
NPCHART Statement 
See SHWNP4 in the SAS/QC Sample Library 
The following statements
create a SAS data set named BATTERY, which contains the
number of alkaline batteries per lot failing an acceptance test.
The number of batteries tested in each lot varies
but is approximately 150.
data battery; length lot $3; input lot nfailed sampsize @@;; label nfailed ='Number Failed' lot ='Lot Identifier' sampsize='Number Sampled'; datalines; AE3 6 151 AE4 5 142 AE9 6 145 BR3 9 149 BR7 3 150 BR8 0 156 BR9 4 150 DB1 9 158 DB2 4 152 DB3 0 162 DB5 9 140 DB6 7 161 DS4 6 154 DS6 1 144 DS8 5 154 JG1 3 151 MC3 8 148 MC4 2 143 MK6 4 150 MM1 4 147 MM2 0 150 RT5 2 154 RT9 8 149 SP1 3 160 SP3 9 153 ;
The variable NFAILED contains the number of battery failures, the variable LOT contains the lot number, and the variable SAMPSIZE contains the lot sample size. The following statements request an np chart for this data:
title 'Number of Battery Failures'; symbol v=dot c=yellow w=1; proc shewhart data=battery; npchart nfailed*lot / subgroupn = sampsize outlimits = batlim turnhlabels cframe = vibg cinfill = vlibg cconnect = yellow coutfill = salmon; label nfailed = 'Number Failed'; run;
The chart is shown in Output 37.3.1, and the OUTLIMITS= data set BATLIM is listed in Output 37.3.2.
Output 37.3.1: An np Chart with Varying Subgroup Sample Sizes

The SHEWHART procedure provides various options for working with unequal
subgroup sample sizes. For example,
you can use the LIMITN= option to specify a fixed
(nominal) sample size for computing the control limits,
as illustrated by the following statements:
title 'Number of Battery Failures'; proc shewhart data=battery; npchart nfailed*lot / subgroupn = sampsize limitn = 150 alln cconnect = yellow cframe = vibg cinfill = vlibg coutfill = salmon; label nfailed = 'Number Failed'; run;
The ALLN option specifies that all points (regardless of subgroup sample size) are to be displayed. By default, only points for subgroups whose sample size matches the LIMITN= value are displayed. The chart is shown in Output 37.3.3.
Output 37.3.3: Control Limits Based on Fixed Subgroup Sample Size
Chapter Contents 
Previous 
Next 
Top 
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.