D
DJN
Having been advised that the data in a control chart should be a normal distribution, I now ask the question; how do I test for normality? And, should I be testing all the data or just the averages?
David
David
Yes, that's the visual or eyeball test for normality - does the distribution appear bell shaped- single peak and tapering off equally on both sides.M Greenaway said:
I believe there may be some mathematical way to test for normality, however it is far easier to plot a histogram of results and just look to see if the distribution appears to look like a normal distribution curve.
The central Limit theorem states that as the sample size becomes large the distribution of means approximates normal regardless of the distribution of original values. This distribution of means is centered at the mean of raw data values. However, the Std. Deviation of means is s/sqrt(N), where s=std.dev.of raw data & N=sample sizeDJN said:
OK easily done, but should the histogram be based on all the data or just the averages?
David
Having been advised that the data in a control chart should be a normal distribution, I now ask the question; how do I test for normality? And, should I be testing all the data or just the averages?