# Proportion for three level

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• #32242

ROSS
Member

I’m chosing the best technical method(total three technical methods) for the production yield, as we know, we can use two-proportions test to compare the  two level proportion or chose the better one, but could someone tell us how can we compare the proportion or choice the best one in three level?

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#85917

Zilgo
Member

The easiest way to accomplish this task is to perform the 2 Proportion test multiple time.  Since there are only three comparisons to perform (1v2, 1v3, 2v3) this isn’t really very tedious or time consuming, as it would be if you had like eight proportions to compare.  This will at least give you the three confidence intervals you need to compare.  Hopefully you will be able to make a decision from those results.

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#85923

Carl H
Participant

Good question.
I have used 1 way anova in Minitab and used  one of the optional comparisons methods for the groups.  This provides all the combinations of group comparisons, comparisons with the “control” group or with the “best ofhte rest” (maybe what you are after).
Carl

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#85950

ROSS
Member

Zilgo Carl:
We can perform the 2 Proportion test multiple time(for three levels, it is only three time), but it will be some problems if the lever is more than 3. So, I think , it should has some better tools in Minitab.
Carl: you suggest me to using the ANOVA for this issue, but I have some confusion, as I know, ANOVE require the data must be the continuos and normal distribution, can ANOVA used in proportion test?

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#85951

Sigma Singh
Member

Tony
you can use chi sq test in this case. In Minitab this test is availabe in stat menu under tables.

Sigma Singh

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#85955

ROSS
Member

Sigma Singh£º
I have ever try the chi-suqare test , but still has some problem.
Supposing my data is as belowing:
Method    Total   Defect
1              500      20
2              400      17
3              700      35
How can I use chi-square test to chose the best one?

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#85959

Sigma Singh
Member

Tony
You may refer to “help” in the chi2 test.
In your case enter data in 3 columns:
Metod 1   method2     method3
480       383             665     (this data represents ok pcs)20         17                 35     (this refers to non conforming pcs)
go to stat/tables/chisq test.
look at the p value (gloden rule never changes – making life simpler for lesser mortals like us)
In this case it is 0.685. So there is no difference between three methods

Sigma Singh

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#85968

ROSS
Member

Sigma Singh:
For chi-square test, we can get the information that method is the significant X to yield(Y) or not, but what I want to know is which method is the best. Can chi-square test reach the purpose?

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#85993

Sigma Singh
Member

Tony
If chisq test says is significant – different methods give different yields, probably you can look at values of proportions to know which is largest / smallest.
Sigma Singh

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