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3-AFC (Alternative Forced Choice)

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PostPosted: Fri Jun 09, 2006 11:00 am    Post subject: 3-AFC (Alternative Forced Choice) Reply with quote

How do I set up a 3-AFC (Alternative Forced Choice) Test in SIMS ?


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PostPosted: Fri Jun 09, 2006 11:14 am    Post subject: 3-AFC (Alternative Forced Choice) Reply with quote

For the THRESHOLD Testing discussion please skip to next message posting below.

3-AFC (Alternative Forced Choice)

2 sample test, 3 presented

Yes, this design is possible in your SIMS software. From our experience and recent Internet research on the AFC topic, it is evident that this type of Sensory test is not commonly used. And when used, AFC tests seem to be in a variety of strategies and tests methods and question designs. Thorough understanding of desired test objectives is important for selecting proper AFC design. Terms like stimuli, individual panelist thresholds, panelist calibration, series, concentrations, steps, ratios, etc are unique to AFC studies. It is complex.

The best reference document we found regarding AFC tests is ASTM E1432-04(2004) titled Standard Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of Intermediate Size. Notably Paragraph 4.1.

Whatever AFC method is being considered, individual panelists are a focus of AFC, resulting in this key sentence from ASTM document: "There is a large degree of random error associated with estimating the probability of detection from less than approximately 500 3-AFC presentations."

Sensory Triangle Tests A A B B are much more common as are Duo-Trio Tests.

SIMS Basic Design Notes for 3-AFC

For setup in your SIMS software, 3-AFC are simply a "2 sample" Discrimination Test, where Panelists see 3 presented, similar to a typical triangle test A A B B.

Sample Presentation Strategy:
Typical Triangle: A A B B , where A or B is shown Once/Twice, and either can be the Unique Sample.

3-AFC (Alternative Forced Choice): A B B , where A is always shown once and is the Unique Sample.
(the presentation order can change, such as A B B, B A B, B B A)

One terminology saw referred to AFC as a Triangle Constant, vs a typical Triangle Rotated.

SIMS Program Steps:

1. Create your new Discrimination Ballot. Add Triangle Attribute question.

2. Create your new Experimental Design.
2a. Specify TWICE the number of Panelists you'll actually need.
2b. Select Experimental Plan: Discrimination Triangle (DTRI)

3. Create your SIMS software Test Definition.
3a. View Rotation Plan for acceptability.
Note that it is OK that Rotation Plan includes all Sample Sets of a typical Triangle Test Design A A B B. For your AFC Test, you're only going to use the Sample Sets sets needed for AFC Design A B B. This is why we specified TWICE the Panelists in 2a. above.

4. Create your new Result Master Test Execution.
4a. Select Sample Set Selection: Force Panelist to Register Sample Set as Ballot.

5. Execute your test. Only use the Rotation Plan's Sample Set #s which meet you AFC Design A B B. You'll need to indicate on your panelists trays, instructions, laminated cards, etc. what the Sample Set # is. The Panelist is going to Register Sample Set as Ballot at start of test.

This process is closely identical to a typical Triangle test, except for the actual intentional presentation of Rotation Plan Sample Sets A B B.

3-AFC Test Result Interpretation

Sensory Computer Systems can not assist in your Interpretation of the data. Interpretation is really about your objectives, panelists, methods, risk tolerance, culture. All of the SIMS standard Discrimination reports are available in your SIMS software, and most importantly in this 3-AFC case, full Test Data Export support to Microsoft Excel, SAS, JMP, SPSS, etc. Individual Panelist ratios are important to 3-AFC data results interpretation, each and every Threshold Concentration Level for Each Panelist.

Final note about AFC individual panelist thresholds and panelist calibration.
An alternate way to think about the design in SIMS software is to focus on the above sentence "Individual Panelist ratios are important to 3-AFC data results interpretation". If this is the case with your test objectives, then consider setting up a separate SIMS Test for each panelist exclusively, the experimental design for Anonymous Panelists, have each panelist take all Anonymous Sample Sets. For the responses for the panelist, calculate the % ratio correct, aka the threshold. Repeat the process for each of your desired Panelists(n). This is where the 500+ presentations mentioned in the ASTM document can quickly occur. In the end, this will give you a set of (n) ratios (per concentration), which can then be interpreted thru guidelines in the ASTM Documents.

Supportively yours,

John Ream
Sensory Computer Systems
New Jersey 07922 USA
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PostPosted: Tue Jun 16, 2015 3:04 pm    Post subject: Threshold Testing Reply with quote

Threshold Testing

Threshold testing in SIMS.

Threshold testing is by a forced-choice series of triangle presentations, such as by ascending formula concentrations. Basically it is a 3-AFC but instead of a randomized order, the samples are seen in order of concentration (min of 10 concentrations). When a panelist identifies the “test” sample as sweeter 2x in a row the test is ended. The data is analyzed using a geometric mean. This is most like the example in the ASTM doc appendix (X1) Differences threshold of Ethyl Acetate Added to Beer

11 C3 R10 (11 samples, 3 presented, 10 reps.) Where Sample 1 is “Blank” and next 10 samples are concentrations in rising order.

A series of Affective Hedonics 3-point (like triangles), 10 reps, 1,1,2 ... 1,1,3 ... 1,1,4 ... ... 1,1,10 ... 1,1,11
2 blanks and 1 concentrate is seen with each triangle presentation.

Ballot: Affective ballot, 1 attribute: Hedonic 3-point, data export label 'Triangle'.

Experimental Design: 11 samples, 3 presented, 10 reps. Select Randomized Sample Presentation to ensure order balance.
Sample #1 = Control
Sample #2 = Concentrate #1
Sample #3 = Concentrate #2
Sample #11 = Concentrate #10

From ASTM E679, the standard procedure for panelists:
7.1 The panelist begins judging with that set which contains the test sample with the lowest concentration (highest dilution)
of the odorous or sapid substance, takes the time needed to make a selection, and proceeds systematically toward the higher concentrations.
7.2 Within each set, the panelist indicates that sample which is different from the two others (detection threshold)
or which exhibits a recognizable odor or taste of the substance (recognition threshold).
If the panelist cannot readily discriminate, a guess must be made so that all data may be utilized.
7.3 The judgments are completed when the panelist either
(1) completes the evaluation of all sets of the scale, or
(2) reaches a set wherein the test sample is correctly identified, then continues to choose correctly in higher concentration test sample sets.

Raw Data Export, use option [X] If Caption is BC then display the Absolute Sample # selected.
This makes it quick-n-easy to see if panelist choose the blank (1) or the concentrate (any #>1)
And use option (*) Sort When Multiple Rep Tests Sort by Panelist, Rep

A SIMS Express Package of an example Threshold Test is available.

See ASTM R679 "Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits"

Last edited by ForumAdmin on Wed Dec 16, 2015 2:49 pm; edited 4 times in total

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PostPosted: Wed Dec 16, 2015 12:18 pm    Post subject: Threshold Testing Reply with quote

Threshold Testing

SIMS software express package of the following example: THRESHOLD.SIMS2000ExpressPackage.sql.ZIP

Questionnaire Example:

Setup Questionnaire Example:

Test Definition Example:

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