How do you analyze non-normal data in Minitab?
In Minitab, select Stat > Quality Tools > Capability Analysis > Nonnormal… Populate the “Capability Analysis (Nonnormal Distribution)” dialogue box as seen below. Make sure to select “Exponential” next to Fit distribution. Then, Click on “Options”.
Can you calculate CPK on non-normal data?
With non-normal data, it is wrong to calculate a Cpk based on the raw data. A better approach is to determine what distribution best fits your process and data and then use the non-normal Ppk approach. The equations for Ppk are different for non-normal data than for normally distributed data.
How do you calculate LSL and USL in Minitab?
Examples of upper and lower specification limits
- LSL = 2.5 USL = 2.687. The lower specification is 2.500 inches and the upper specification is 2.687 inches.
- LSL = 80. Often, only one specification limit is used.
- USL = 30. Conversely, consider a call center where calls must be answered within 30 seconds.
What should I do if data is not normal?
Many practitioners suggest that if your data are not normal, you should do a nonparametric version of the test, which does not assume normality. From my experience, I would say that if you have non-normal data, you may look at the nonparametric version of the test you are interested in running.
How do you Analyse non-normal data?
There are two ways to go about analyzing the non-normal data. Either use the non-parametric tests, which do not assume normality or transform the data using an appropriate function, forcing it to fit normal distribution. Several tests are robust to the assumption of normality such as t-test, ANOVA, Regression and DOE.
How do you convert non-normal data to normal data?
Box-Cox Transformation is a type of power transformation to convert non-normal data to normal data by raising the distribution to a power of lambda (λ). The algorithm can automatically decide the lambda (λ) parameter that best transforms the distribution into normal distribution.
What does PPK mean in Minitab?
Ppk is a measure of the overall capability of the process and equals the minimum of PPU and PPL. Ppk is a ratio that compares two values: The distance from the process mean to the closest specification limit (USL or LSL) The one-sided spread of the process (the 3-σ variation) based on its overall variation.
Can you do a two sample t-test with non normal?
For a t-test to be valid on a sample of smaller size, the population distribution would have to be approximately normal. The t-test is invalid for small samples from non-normal distributions, but it is valid for large samples from non-normal distributions.