Eliud Kipchoge
Registered
Hello,
I'm currently working with data from three consecutive batches. I want to calculate and compare Cp and Cpk for every batch. Only first batch follows a normal distribution (passes AD test), while the others, don't. Box-Cox transformation yields good results for those two batches.
Q1: Should I transform all three batches? Or just leave the normal-distributed batch and transform the non-normal? Again my objetive is to calculate Cp/Cpk so I don't know if I can "compare" values if I transform only 2 batches...
Q2: I'm transforming my data with optimal λ as calculated by Minitab, which is λ = 4 for 2nd batch and λ =3 for third one. Can I transform (and compare) using different λ? Or should I use same λ for all batches?
We also calculate Ppk (and other long term process parameters) using Excel as required per client. If my understanding is correct, I should use on Excel the already transformed data for this parameters, right? If then - can Minitab provide me with the transformed dataset? I'm assuming that calculating Cp Cpk with transformed data and Ppk with non-transformed would be a huge red flag.
I've tried to find information on the internet but couldn't really solve this issues. I'm attaching my data just in case it is useful (upper bound is 2.5, no lower bound).
Thank you so much for your time.
I'm currently working with data from three consecutive batches. I want to calculate and compare Cp and Cpk for every batch. Only first batch follows a normal distribution (passes AD test), while the others, don't. Box-Cox transformation yields good results for those two batches.
Q1: Should I transform all three batches? Or just leave the normal-distributed batch and transform the non-normal? Again my objetive is to calculate Cp/Cpk so I don't know if I can "compare" values if I transform only 2 batches...
Q2: I'm transforming my data with optimal λ as calculated by Minitab, which is λ = 4 for 2nd batch and λ =3 for third one. Can I transform (and compare) using different λ? Or should I use same λ for all batches?
We also calculate Ppk (and other long term process parameters) using Excel as required per client. If my understanding is correct, I should use on Excel the already transformed data for this parameters, right? If then - can Minitab provide me with the transformed dataset? I'm assuming that calculating Cp Cpk with transformed data and Ppk with non-transformed would be a huge red flag.
I've tried to find information on the internet but couldn't really solve this issues. I'm attaching my data just in case it is useful (upper bound is 2.5, no lower bound).
Thank you so much for your time.