Chapter Contents |
Previous |
Next |
MRCHART Statement |
A subgroup range R_{i} is included in the calculation only if .The unbiasing factor d_{2}(n_{i}) is defined so that, if the observations are normally distributed, the expected value of R_{i} is equal to .Thus, is the unweighted average of N unbiased estimates of .This method is described in the ASTM Manual on Presentation of Data and Control Chart Analysis (1976).
A subgroup range R_{i} is included in the calculation only if , and N is the number of subgroups for which n_{i} geq 2. The MVLUE assigns greater weight to estimates of from subgroups with larger sample sizes, and it is intended for situations where the subgroup sample sizes vary. If the subgroup sample sizes are constant, the MVLUE reduces to the default estimate.
See Example 36.1 for illustrations of the default and MVLUE methods.
Chapter Contents |
Previous |
Next |
Top |
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.