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melinda_thielba

Joined:

May 27, 2014

Sensory Analysis: Simple Discrimination Tests

This Add-In creates an easy interface to some of the most common sensory tests: Triangle Test, Duo-Trio Test, Paired Comparison, and 2-Out-Of-5 tests.
Each of these is a chi-squared tests of proportions, with a given pair of probabilities for a "right" answer under the null hypothesis that the samples are not different. An example test for the Triangle Test and the original script are included with the Add-In.

The data table should contain a binary column to be tested. This column must have the Modeling Type Nominal. For best results with the Triangle Test and 2-Out-Of-5 Tests, assign a value label with Yes/No or Correct/Incorrect to ensure that the porportions are assigned properly. 

The JMP documentation shows an example of the Test of Proportions.

Comments
paulp

Adding sensory tests is a nice feature.  I use triangle tests a lot. How do I access the example for the Triangle Test?  I have the add-in installed, and can open it. However, I don't see where the sample data is installed -- I looked in the Sample Data Library,is that where it's located?   Thanks, Paul

melinda_thielba

Hi, Paul! My apologies. I didn't realize that you can't access a file packaged with an AddIn. 

 

I've attached the file to the original post instead. Please make sure you have the current version. I uploaded a fresh copy yesterday. Please also let me know if you have questions or problems!

melinda_thielba

And apparently there is a way to get to the sample data I packaged with the AddIn.

In JMP,

1) Go to View->AddIns.

2) Click the name of the Addin in the window that appears

3) Click the hyperlink for the addin Home folder. 

paulp
Hello Melinda, thank you for your reply and for pointing me to the data.

I have a question --what was the alternative hypothesis used? I'm thinking that it should be that the proportion of Correct Answers > 0.3333, because that is evidence that there is truly a difference between products A and B. The triangle test is a discriminatory test, so we care about whether panelist choose the correct answer more than would be expected by chance.

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When I ran the test with the one-sided alternative hypothesis, I got a slightly different probability than was in the Distribution script supplied with the sample data. Not sure if this 2-sided Chi-Square test was intended to represent a triangle test.

[cid:image002.png@01D2D0B0.86FD89B0]


Regards, Paul

melinda_thielba

Hi, Paul. 

The Chi-Squared is always a one-sided test. StatsExchange over on StackOverflow has a nice discussion on this.

So, following the guidelines on SensorySociety.org, the stated p-values are correct.  

One could argue that we should perform a two-sided test instead. JMP offers that as an exact binomial test. 

Capture.JPG

 

 

 

That test is not as well-known, and I haven't seen it recommended in the sensory analysis literature. I feel like I'm in a bit of a bind when it comes to reporting p-values for the user. The software is written to spec, but maybe it's not what a statistician would recommend generally. 

What's your opinion? 

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