Analyse results
from the A-not-A test.

- Discrimination_AnotA.xls
- Data type is binary.

The A-not-A discrimination test is a variation of the paired comparison test. It is an unspecified test with a probability of guessing of 0.5.

The panellist is presented with the first product (A), which is then removed after evaluation.

A second product is then presented,
and the panellist decides whether it is the same as A or not. As
part of the test design multiple products may be compared with A in a monadic
protocol. The order of the samples is randomized.

**Treat Sessions/Replicates separately:**If the data has been gathered over different sessions, or there are different replicates, these can be analysed separately.**Reference Product:**Select which product should be your reference product. This is the first product in the test(A).**Correction:**If yes, apply the continuity correction for 2x2 contingency tables.**Number of Decimals for Values:**Required number of decimals for values given in the results.**Number of Decimals for P-Values:**Required number of decimals for any p-values given in the results.

- Contingency table: This is a n x 2
contingency table of the responses, where n is the number of products.

The first row totals the responses when the reference product (A) was tested.

Subsequent rows total the responses when the other products were tested. - A chi-squared test is then performed on the
contingency table. The following values are returned:
- Chi-squared value
- The Critical Chi-Squared value at a 5%
significance
- Degrees of freedom
- P-value at 5% significance

If the p-value is < 0.05 for the chi-squared test, it can be concluded that the reference product (A) is significantly different to the other products. Note that even if you conclude a difference, this does not imply similarity.

- D-prime. D-prime indicates the size of the difference between the products. The following values are returned:

- d-prime
- Lower and upper 95% confidence intervals for d-prime
- P-value for Fisher’s Exact Test performed on the contingency table.
Note that if one of the cells in the contingency table is zero, the d-prime cannot be calculated.

- The R package
*sensR*(Rune Christensen and Per B. Brockhoff) is used. - The
*AnotA*function is used to calculate d-prime.

- ISO 8588:1987 – Sensory Analysis
– Methodology – ‘A’ – ‘not A’ Test
- Lawless, H.T. and Heymann,
H. (2010). Sensory Evaluation of Food – Principles and
Practices. Springer.

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