ASTM-E2262:03(R2020) pdf free download – Standard Practice for Estimating Thurstonian Discriminal Distances.
“A” sample and the other sample is selected to he the “Not-A” sample. Choice proportions are tallied for each sample and the values of d’ and its variance, S2(d’), are obtained from Tables XI.9 and Xl.IO, respectively, by the same techniques used in the A/Not-A method.
5. Significance and Use
5.1 Under the assumptions of the model, the Thurstonian model approach to measuring the perceived difference between two samples (whether overall or for a specific attribute) is independent of the sensory method used to collect the data. Converting results obtained from different test methods to d’ values permits the assessment of relative differences among samples without requiring that the samples be compared to each other directly or that the same test methods be used for all pairs of samples.
5.2 Thurstonian scaling has been applied to:
5.2.1 Creating a historical database to track differences between production and reference samples over periods in which different test methods were used to measure the di ife ren ce,
5.2.2 Comparing the relative sensitivities of different user
groups and consumer segments.
5.2.3 Comparing trained panels that use different measuring techniques.
5.2.4 Comparing the relative sensitivities of consumers versus trained panels.
5.2.5 Comparing different methods of consumer testing (for example. CLT versus HUT, preference versus hedonic scales. etc.), and
5.2.6 Comparing different discrimination test methods.
6. Procedure
6.1 Forced-choice Methods—The relationship between and the expected choice proportion. !‘., is different for different forced-choice methods because the decision rule used by the assessors varies from one method to another (see Appendix X3). As a result, different tables are required to estimate depending on the method used. Tables for the four most commonly used methods are presented. The estimated value of (that is. d’) is obtained as follows:
6.1.1 Compute the observed choice proportion as = xlii. where x is the observed number of correct responses and ii is the sample size.
Duo-Trio (Table X 1.3), 3-AFC (Table X 1.5), or 2-AFC (Table X 1.7). Find the entry in the table that is closest to the observed value of pt.. The value of d1, accurate to one decimal place. is the row-label of the table corresponding to the selected entry. The second decimal place of d’ is the column-label of the table corresponding to the selected entry.
6.1.3 Obtain the estimated variance of d as follows. Enter the appropriate table in Appendix X 1: triangle test (Table X 1.2), Duo-Trio (Table X 1.4), 3-AFC (Table X 1.6), or 2-AFC (Table X1.8). Find the value of B in the row and column that correspond to the value of ci’ obtained in 6.1.2.