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Burr Weighting Factors
The table below presents the factors used to provide a minimum variance linear unbiased estimate of the standard deviation from sample ranges (e, f) or sample standard deviations (g, h), based on the subgroup size. (see reference: Burr (1969)).
See also: Fixed or Varying Subgroup Sizes for X-Bar charts
The factors e and f are used to stabilize the estimate of Process Sigma based on the Range Chart; factors g and h are used to stabilize the estimate of Process Sigma based on the Sigma Chart.
|
Subgroup Size |
e |
f |
g |
h |
|
2 |
1.553 |
1.752 |
2.196 |
1.752 |
|
3 |
2.145 |
3.63 |
4.130 |
3.660 |
|
4 |
2.660 |
5.476 |
6.094 |
5.615 |
|
5 |
3.115 |
7.246 |
8.074 |
7.589 |
|
6 |
3.524 |
8.931 |
10.060 |
9.572 |
|
7 |
3.895 |
10.535 |
12.051 |
11.561 |
|
8 |
4.236 |
12.061 |
14.044 |
13.553 |
|
9 |
4.551 |
13.517 |
16.038 |
15.546 |
|
10 |
4.844 |
14.908 |
18.034 |
17.541 |
|
11 |
|
|
20.031 |
19.537 |
|
12 |
|
|
22.028 |
21.534 |
|
13 |
|
|
24.026 |
23.531 |
|
14 |
|
|
26.024 |
25.529 |
|
15 |
|
|
28.022 |
27.527 |
|
16 |
|
|
30.021 |
29.525 |
|
17 |
|
|
32.019 |
31.523 |
|
18 |
|
|
34.018 |
33.522 |
|
19 |
|
|
36.017 |
35.521 |
|
20 |
|
|
38.016 |
37.520 |
Learn more about the SPC principles and tools for process improvement in Statistical Process Control Demystified (2011, McGraw-Hill) by Paul Keller, in his online SPC Concepts short course (only $39), or his online SPC certification course ($350) or online Green Belt certification course ($499).
