Degree of Difference Method

Degree of difference testing, commonly abbreviated DOD, is a discrimination method used to determine if an overall difference exists between test and control products when the product shows inherent variability due to preparation, production time, multiple components, etc. With such variability, traditional 3-AFC and 2-AFC methods¹ cannot effectively separate true treatment variability from normal product variability, and therefore can give false results. Examples of heterogeneous products include prepared meals such as soups or entrees, baked goods such as cookies or rolls, and multi-component snack mixes.

An approach utilizing degree of difference (DOD) testing was proposed by Aust, Gacula, Beard, and Washam (1985)² wherein scaled difference ratings were used to contrast the difference between the control and the test samples to a baseline difference between control lots. Panelists scaled overall difference for three pairs of samples – Control lot 1 (C1) vs. C1, C1 vs. Control lot 2 (C2), and C1 vs. Test (T). The difference between the control and test was then compared to within-lot and between-lot variability of the control to establish if the control-test difference was significant.

Recognizing that this standard DOD approach may not detect the situation where Test is outside of normal control lot variability, Pecore, Stoer, Hooge, Holschuh, Hulting and Case³ modified this methodology by doubling comparisons between the control and test lot products by eliminating the C1-C1 pair and adding a C2-T pair. This modified method thus incorporates a measure of control lot variability, and has been abbreviated DOD-CV.

A further extension of this method is to include test lot variability as well, which has recently been published as the DOD-CTV method (Young, Pecore, Stoer, Hulting, Holschuh and Case⁴).

References

¹ Lawless, H. T., & Heymann, H. (1998). Sensory evaluation of food. New York: Chapman & Hall.

² Aust, L. B., Gacula, M. C., Jr., Beard, S. A., & Washam, R. W. II, (1985). Degree of difference test method in sensory evaluation of heterogeneous product types. Journal of Food Science, 50, 511–513.

³ Pecore, S., Stoer, N., Hooge, S., Holschuh, N., Hulting, F., & Case, F. (2006). Degree of difference testing: A new approach incorporating control lot variability. Food Quality and Preference, 17(7–8), 552–555.

⁴ Young, T., Pecore, S., Stoer, N., Hulting, F., Holschuh, N., & Case, F. (2008) Incorporating test and control product variability in degree of difference tests. Food Quality and Preference, 19, 734-736.