The duo-trio test, developed by Peryam and Swartz (1950), represented an alternative to the triangle test that, for some, was a more complex test psychologically. The duo-trio test was found to be useful for products that had relatively intense taste, odor, and/or kinestethetic effects such that may impact sensitivity.
A Duo-Trio Test is an overall difference test which will determine whether or not a sensory difference exists between two samples. This method is particularly useful:
- To determine whether product differences result from a change in ingredients, processing, packaging, or storage
- To determine whether an overall difference exists, where no specific attributes can be identified as having been affected
Compared to Other Overall Difference Tests
The Duo-trio test is equally sensitive to the triangle test and is simple and easily understood. Compared with the Paired Comparison test, it has the advantage that a reference sample is presented which avoids confusion with respect to what constitutes a difference, but a disadvantage is that three samples, rather than two, must be tasted.
Present to each subject an identified reference sample, followed by two coded samples, one of which matches the reference sample. Ask subjects to indicate which coded sample matches the reference. Count the number of correct replies and refer to a table for interpretation. Two design options are available for a duo-trio test. The conventional approach is a balanced the reference between the control and test products; however in some situations, the reference may be kept constant.
All should be familiar with the format, task, and evaluation procedure for the Duo-Trio Test. An orientation session is recommended prior to the actual test to familiarize subjects with the test procedures and product characteristics.
As a general rule, the minimum is 16 subjects, but for less than 28, the beta-error is high. Discrimination is much improved if 32, 40, or a larger number can be employed.
Offer samples simultaneously, if possible, or else present samples sequentially. Prepare equal numbers of the possible combinations (control and tests) and allocate the sets in a balanced design among the subjects. Space for multiple Duo-trio tests may be provided on the scoresheet, but do not ask supplementary questions (e.g., the degree or type of difference or the subject’s preference) as the subject’s choice of matching sample may bias his or her response to these additional questions. Count the number of correct responses and the total number of responses. Do not count “no difference” responses; subjects must guess if in doubt.
1 Meilgaard, M., G. V. Civille and B. T. Carr (2007). Sensory Evaluation Techniques, 4th Ed. New Boca Raton, FL: CRC Press, 6: 72 – 79.
2 Stone, H., and Sidel., J.L. (2004). Sensory Evaluation Practices, 3rd edition. Elsevier Academic Press, San Diego, CA, 5: 152-153.