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
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.