[See SHWXR2 in the SAS/QC Sample Library]This example illustrates how you can apply tests for special causes to make and charts more sensitive to special causes of variation.
The weight of a roll of tape is measured before and after an adhesive is applied. The difference in weight represents the amount of adhesive applied to the tape during the coating process. The following data set contains the average and the range of the adhesive amounts for 21 samples of five rolls:
data Tape; input Sample $ WeightX WeightR; WeightN=5; label WeightX = 'Average Adhesive Amount' Sample = 'Sample Code'; datalines; C9 1270 35 C4 1258 25 A7 1248 24 A1 1260 39 A5 1273 29 D3 1260 21 D6 1259 37 D1 1240 37 R4 1260 28 H7 1255 19 H2 1268 36 H6 1253 36 P4 1273 29 P9 1275 22 J7 1257 24 J2 1269 41 J3 1249 36 B2 1264 31 G4 1258 25 G6 1248 36 G3 1248 30 ;
The following statements create and charts, apply several tests to the chart, and tabulate the results:
title 'Tests for Special Causes Applied to Adhesive Tape Data'; ods graphics on; proc shewhart history=Tape; xrchart Weight*Sample / tests = 1 to 5 odstitle = title tabletests zonelabels; run;
title 'Tests for Special Causes Applied to Adhesive Tape Data'; proc shewhart history=Tape; xrchart Weight*Sample / tests = 1 to 5 odstitle = title tabletests nochart zonelabels; run;
The charts are shown in Output 15.38.1, and the table is shown in Output 15.38.2. The TESTS= option requests Tests 1, 2, 3, 4, and 5, which are described in Tests for Special Causes: SHEWHART Procedure. The TABLETESTS option requests a basic table of subgroup statistics and control limits with a column indicating which subgroups tested positive for special causes.
The ZONELABELS option displays zone lines and zone labels on the chart. The zones are used to define the tests.
Output 15.38.1 and Output 15.38.2 indicate that Test 1 is positive at sample D1 and Test 5 is positive at sample P9. Test 1 detects one point beyond Zone A (outside the control limits), and Test 5 detects two out of three points in a row in Zone A or beyond.
Tests for Special Causes Applied to Adhesive Tape Data |
Means and Ranges Chart Summary for Weight | ||||||||
---|---|---|---|---|---|---|---|---|
Sample | Subgroup Sample Size |
3 Sigma Limits with n=5 for Mean | Special Tests Signaled |
3 Sigma Limits with n=5 for Range |
||||
Lower Limit |
Subgroup Mean |
Upper Limit |
Lower Limit |
Subgroup Range |
Upper Limit |
|||
C9 | 5 | 1241.7065 | 1270.0000 | 1276.8650 | 0 | 35.000000 | 64.441879 | |
C4 | 5 | 1241.7065 | 1258.0000 | 1276.8650 | 0 | 25.000000 | 64.441879 | |
A7 | 5 | 1241.7065 | 1248.0000 | 1276.8650 | 0 | 24.000000 | 64.441879 | |
A1 | 5 | 1241.7065 | 1260.0000 | 1276.8650 | 0 | 39.000000 | 64.441879 | |
A5 | 5 | 1241.7065 | 1273.0000 | 1276.8650 | 0 | 29.000000 | 64.441879 | |
D3 | 5 | 1241.7065 | 1260.0000 | 1276.8650 | 0 | 21.000000 | 64.441879 | |
D6 | 5 | 1241.7065 | 1259.0000 | 1276.8650 | 0 | 37.000000 | 64.441879 | |
D1 | 5 | 1241.7065 | 1240.0000 | 1276.8650 | 1 | 0 | 37.000000 | 64.441879 |
R4 | 5 | 1241.7065 | 1260.0000 | 1276.8650 | 0 | 28.000000 | 64.441879 | |
H7 | 5 | 1241.7065 | 1255.0000 | 1276.8650 | 0 | 19.000000 | 64.441879 | |
H2 | 5 | 1241.7065 | 1268.0000 | 1276.8650 | 0 | 36.000000 | 64.441879 | |
H6 | 5 | 1241.7065 | 1253.0000 | 1276.8650 | 0 | 36.000000 | 64.441879 | |
P4 | 5 | 1241.7065 | 1273.0000 | 1276.8650 | 0 | 29.000000 | 64.441879 | |
P9 | 5 | 1241.7065 | 1275.0000 | 1276.8650 | 5 | 0 | 22.000000 | 64.441879 |
J7 | 5 | 1241.7065 | 1257.0000 | 1276.8650 | 0 | 24.000000 | 64.441879 | |
J2 | 5 | 1241.7065 | 1269.0000 | 1276.8650 | 0 | 41.000000 | 64.441879 | |
J3 | 5 | 1241.7065 | 1249.0000 | 1276.8650 | 0 | 36.000000 | 64.441879 | |
B2 | 5 | 1241.7065 | 1264.0000 | 1276.8650 | 0 | 31.000000 | 64.441879 | |
G4 | 5 | 1241.7065 | 1258.0000 | 1276.8650 | 0 | 25.000000 | 64.441879 | |
G6 | 5 | 1241.7065 | 1248.0000 | 1276.8650 | 0 | 36.000000 | 64.441879 | |
G3 | 5 | 1241.7065 | 1248.0000 | 1276.8650 | 0 | 30.000000 | 64.441879 |