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I believe the traditional GRR method calculates the percentage R&R incorrectly because they add standard deviations instead of variances. I assume this is the reason that %RR and %PV do not add up to 100. When I compare these percentages to the Anova results (% contributed) they are very different. A recent sdtudt resulted in %RR=10.26 vs. %RR=1.9669 (Anova).
Which method is considered most accurate? I find Wheeler's EMP studies much more intuitive than either of these. Also, does the Anova method compares measurement variance to the study parameters or specifications?
Thanks,
Rich DeRoeck
Which method is considered most accurate? I find Wheeler's EMP studies much more intuitive than either of these. Also, does the Anova method compares measurement variance to the study parameters or specifications?
Thanks,
Rich DeRoeck
A while back I received a PPAP submission that included an ANOVA GR&R study report. I asked the supplier's QM why he chose ANOVA over average-and-range (which is, as you say, the de facto standard). There was a moment of silence, after which he said that he'd have to check on it and get back to me. He called back a few hours later saying that A) he had been unaware until my phone call that there were different methods, and B) his gage tech told him that he used the ANOVA calculations because the average-and-range results were "too high." 