Run Chart in Minitab - Can I use Run Chart for Normality Test in Minitab

E

Ehsan Heidari

#1
1- Can I use Run chart for normality test in minitab?
2- I attached example of doing run chart with real data, what`s your analysis on it? I want to know the means of each report!!!
 

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sunff114

#2
Re: Run Chart in minitab

The sample mean is the red square if you didn't change the default set in minitab, and the black dots stand for the observations in each subgroup.
 
J

JasonAREdwards

#3
Re: Run Chart in minitab

I do not see how you could use a run chart to understand if your data follows a normal distribution. You need to understand the mean, variance and total data under the curve. Not sure that you could comprehend that from a run chart.
 

Miner

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#4
The run chart will only tell you in a crude fashion, whether your process is stable, not whether it is Normal.

This one is flagging Clustering as statistically significant. This may be due to the rather obvious measurement resolution problem in the data, a possible shift in the last 5 subgroups, or both.
 
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A

Al Dyer

#5
Ehsan,

Miner has it down. Could you rework the data in Minitab by entering differing sub-group sizes and review the expected differences? Maybe start with a new sub-group of five then work your way back to the subgroup of one? Run charts are notoriously unreliable.

Al...
 
E

Ehsan Heidari

#6
Ehsan,

Miner has it down. Could you rework the data in Minitab by entering differing sub-group sizes and review the expected differences? Maybe start with a new sub-group of five then work your way back to the subgroup of one? Run charts are notoriously unreliable.

Al...
My subgroup size is 5, I attached data.
 

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bobdoering

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#7
To the original question: can a run chart show data is normal? Oh, if it was just that easy...we would all have an easier life. No - if it is normal it may appear a particular way, but that is a very high level judgment. Not very convincing.

Here is how it goes.

1. Do a run chart to see if there is any obvious issues to address prior to statistical analysis.

2. Do a curve fit analysis. It is the best way to determine normality.

The attached data shows by curve fit it is not normal.

3. Now the question becomes why is it not normal. Instability? Special cause?

Chart the data - preferably with the correct chart. You stated you took 5 part samples. The attached X-bar R charts show out of control conditions. So, you go back to the copious notes taken during the run (operator change, shift change, any stop/start, any material change, any adjustment) and see if the notes indicate why there was any shifts. If you have reason to remove them, then analyze the data without the shift - but not until you understand the source of the shift.
 

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