Ford's answers to the NHTSA 6.7 Investigation

Weibull wrote:

1 of the failures was a different failure mode, unrelated to the HPFP altogether. So that one is excluded, but we had another one yesterday so the number still stands at 14 for the 2011 models as best I can determine similar failure modes. Someone fat fingered one of the failure mileages to have 50k more miles on it than it really did so I corrected that one. Failure slope changed a bit with the inclusion, exclusion, and correction of relevant failure mileages, and is now 2.558

Waaaait!

The immediate problem with using the statistical approach you have chosen is you have assumed that it is a normal distribution.

Concur with you that the sample size you have is at the lower range of acceptability to presume normal distribution --- but the issue that keeps coming to mind is... can it be non normal.

A different FMEA approach is to not concentrate on the central tendency, but on the outliers and ask yourself, why are the outliers there?

I once came across an issue where something coming off the line kept failing --- and the people on the line actually KNEW why each one that came off was a dud --- because they can sense it "felt" different.

Another example was from a case where operators A B and C were all making the same parts, but Operator C constantly had his dies last a lot longer. Reason: Operator C came in 30 min early, turned on the heaters to warm the die before he started his shift.

Hence, statistically, in this case, the central tendency (A and B) told you nothing useful --- but the answer was in detailed observation of C.