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Fishers Exact Test Interpretation

Hello! I am analyzing an experiment that I conducted which was made using JMP DOE.  I am interested in using the Fishers Exact Test results (pictured below). I was doing some reading on the JMP help site and it says that values in the tables are not to be considered as P-Values, can these values be taken has regular probability values or is there another way to interpret the data. 

 

 

MedianPuppy4982_1-1712670529415.png

 

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: Fishers Exact Test Interpretation

They are p-values. Can you send me a link to the page in the documentation from which you interpreted otherwise?

What is your alternative hypothesis in the experiment? Isi it two-sided or one-sided?

View solution in original post

MRB3855
Super User

Re: Fishers Exact Test Interpretation

Hi @MedianPuppy4982  and @Mark_Bailey : I see where the confusion is coming from.

Here: Fisher’s Exact Test Report (jmp.com)

Therein, it says:

"The Fisher’s Exact Test report includes the following information:

Table Probability (P)

     The probability for the observed table. This is not the p-value for the test.

Two-sided Prob ≤ P

     The significance probability (p-value) for the two-sided test."

 

The above is true for the general r x c table case as in my example screenshot below (I have a binary response, and a three level factor) where my table is 3 rows by 2 columns.

MRB3855_0-1712757845184.png

But, in the 2 x 2 case (like @MedianPuppy4982  has)  it gives p-values only as @MedianPuppy4982  output shows. . 

View solution in original post

5 REPLIES 5

Re: Fishers Exact Test Interpretation

They are p-values. Can you send me a link to the page in the documentation from which you interpreted otherwise?

What is your alternative hypothesis in the experiment? Isi it two-sided or one-sided?

MRB3855
Super User

Re: Fishers Exact Test Interpretation

Hi @MedianPuppy4982  and @Mark_Bailey : I see where the confusion is coming from.

Here: Fisher’s Exact Test Report (jmp.com)

Therein, it says:

"The Fisher’s Exact Test report includes the following information:

Table Probability (P)

     The probability for the observed table. This is not the p-value for the test.

Two-sided Prob ≤ P

     The significance probability (p-value) for the two-sided test."

 

The above is true for the general r x c table case as in my example screenshot below (I have a binary response, and a three level factor) where my table is 3 rows by 2 columns.

MRB3855_0-1712757845184.png

But, in the 2 x 2 case (like @MedianPuppy4982  has)  it gives p-values only as @MedianPuppy4982  output shows. . 

Re: Fishers Exact Test Interpretation

Hi @MRB3855

 

Thank you so much for your help! Do we know why that is? or is it just the general rule for 2x2 tables for the Fishers Exact Test?

MRB3855
Super User

Re: Fishers Exact Test Interpretation

Good question @MedianPuppy4982 . My guess is (JMP folks may want to jump in here) that with the 2x2 case there are more direct ways (e.g., based on the binomial distribution) to calculate p-values. In the general rxc case, the p-value is calculated as the sum the probabilities from all tables (with the same row and column totals) having a probability less than or equal the probability of the observed table.  

ParkerGordon
Level I

Re: Fishers Exact Test Interpretation

Thank you so much for the solution.