Minitab 19 Anova or X bar # of distinct catagories

[Floyd73]

Hi, My issue is we are using Anova but discovered that the number of distinct catagories (Minitab 19) is 1, no matter what I do, I have had to deconstruct our previous SPC employees workings out to try and reconstruct it, our guide states to use Anova but when I use Anova the number of distinct catagories is always 1. Today I changed to X bar & R chart which then gave 43 distinct catagories. Will I be ok using X bar & R from now on rather then Anova. This is for fluid testing if that helps.

 

[Miner]

Please provide your data in Excel format. I have Minitab 18 and would like to check this out before answering.

Since you started a thread on this, I will delete your duplicate post in the other thread.

 

[Welshwizard]

Hi Floyd73,

Go back to first principles and check the outputs manually, the formula for ndc is 1.41 x PV/GRR, lots of references for that including the AIAG blue book.

As 1.41 is a constant (derived from the square root of 2) its likely that the difference you are seeing is either the computation for Part Variation (PV) and/or GRR.

This all implies of course that ndc is even useful but that is another story ............