“Gauge Capability and Designed Experiments, Part I,” D.
Weerahandi, Journal of Quality Technology, pp. “Measurement System Assessment Via Generalized Inference,” M. Burdick, et al, Journal of Quality Technology, pp. “A Review of Methods for Measurement System Capability Analysis,” R.
Finally, at least four, and preferably six, operators should be used in the study to get a confidence interval of respectable size for reproducibility. You should make sure you include parts whose measurements span the entire range of the process output (do not use masters or “golden” parts). In addition, if you have a choice, it is better to run more parts with fewer measurements each than a few parts with many measurements each. Thus, if there is no information available to approximate p 1 and p 2, then 0.5 can be used to generate the most conservative, or largest, sample sizes. Difference of interest: 05 58mph Size Pow' < 40 60 90 100 I 4 6m 17. The values of p 1 and p 2 that maximize the sample size are p 1 p 2 0.5. 19.5 18.0 16.5 15.0 Power What sample size is required to detect a What is the. Eventually, through this trial-and-error approach, you should get (hopefully) very close to the right combination of input factors.īecause of all the above difficulties, and the large number of gage R&R studies need to be done, most of us practitioners have stuck with the 10 parts, three trials, three operators format.įor those who don’t have access to these articles, the authors also recommend using only the ANOVA method for gage R&R studies. In order to estimate the sample size, we need approximate values of p 1 and p 2. If this simulated confidence interval is too large, then make changes (increases) to the number of parts, trials, and operators and compute a second simulated interval. Then, calculate a confidence interval with a particular number of parts, trials, and operators. However, they offer the following approach to get some idea of the appropriate sample size needed.įirst, before conducting the study, make an educated guess at what you think the standard deviation will turn out to be (perhaps based on previous studies of this gage or from studies on similar gages). Unfortunately, the authors conclude that there is no direct formula for determining in advance the number of parts, trials, and operators based on chosen alpha and beta risks. In them, equations and procedures are given for calculating confidence intervals for the various standard deviations that are estimated in a study. The articles listed at the bottom of this post will provide some answers to your questions about gage R&R studies.