Normality test minitab11/30/2023 ![]() ![]() If I dither the data using "small-compared-to-process-variation" normally distributed noise ( $\mu$ = 0, $\sigma$ = 0.005) the distribution does not change in any meaningful way. Looking at the data it indeed appears to be normal, however the Anderson-Darling test gives a p-value of <0.05, indicating non-normal data: ![]() However, due to the resolution of the measuring instrument (reads out to 0.01) and relatively narrow range of values (min: 3.34, max: 3.74), there is a limited number of discrete values the measurement can take. On a physical basis, pH is a continuous scale (being the negative logarithm of the concentration of free hydrogen ions in solution). This dataset will be used to infer process capability using Minitab. I have a dataset with several hundred pH measurements from a factory line.
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