A triangle test is a discriminative form of a sensory analysis. It’s results 1’ ...Indicate whether or not a detectable difference exists between two samples.’. For this reason it is often used 2 ”...in quality control to determine if a particular production run meets the quality control standard.”. To carry out the experiment the panellists must be provided with three (3) coded samples of the products being tested. Two (2) of the samples must be from the same product and panellists must pick the odd one out. The panellists must also be
provided with an other food or beverage to cleanse their palate and to minimise the cross contamination of different sample flavours in the mouth. In addition,
There are nine (9) possible errors which could influence a triangle test:
· Expectation error: This error occurs when the panellists are given more than enough information about the test before actually doing it. Too many facts or hints cause panellists to make a judgement on expectation rather than intuition. For this reason it is important provide only the facts necessary to complete the test. i.e. Random three digit codes on the samples because 1 ‘...People generally associate “1” or “A” with “best” ’, instructions.
· Stimulus error: It is important to mask all differences between the two samples. This is because people generally aspire to get the correct answer and any visible differences will “stimulate” error. Lighting, uniformity of size and shape of samples, the use of transparent or opaque cups...etc. must all be taken into account if this error is to be avoided.
· Logical error: can cause panellists to evaluate samples according to particular qualities because they appear to be 1 “...logically associated with other characteristics.’ To avoid this error uniformity of appearance and disguising of disparities must be dealt with before the experiment takes place.
· Leniency error: Error based on the panellists opinions of the researcher/s. Tests must be conducted in a organised, professional approach.
· Suggestion effect: The suggestion effect is basically the influence of other panellists by voicing their opinions or making known their reactions. Silence and separation of panellists by booth-like partitions help decrease the suggestion effect enormously.
Positional Bias (order effect): Usually the middle sample is chosen as odd. This is common in the triangle test, especially when the samples look close to identical.
This can be avoided by presenting the samples randomly eg: in a triangle shape so that there is no middle sample.
· Contrast effect and convergence error: The juxtaposition of two noticeably diverse samples commonly causes the panellists to exaggerate the contrasts, hence the contrast effect. But this can also incur the opposite effect, whereby the significant difference can camouflage the more minute unlikeness's—The convergence error. In order to correct and prevent these errors, there must be randomized arrangements of samples for each panellist, so as to balance both effects.
· Central tendency Error: Occurs when the panellists rate a sample mid-range, to avoid
extremes. Consequently, results may suggest that samples are more comparable than they are. This becomes apparent especially when the panellist is not accustomed with the products or test procedure. Prevention of this flaw can be achieved by acquainting panellists with the test
approach and products and by randomising the order of arrangement of samples..
· Motivation: Motivation of panel members affects their sensory acuity. It is therefore
important to maintain the interest of the panellists. This can be achieved just by conducting the experiment in a professional, controlled manner, or even by offering a report of their
results. Usually 1 ‘trained panellists are more motivated than those who are not.’
There are many other errors which can occur but the above are the main possible errors. It is evident from the above information that randomisation, control and professional conduct of the experiment are essential for obtaining the most accurate results.
1. Poste L.M, Mackie D.A. , Butler G. , Larmond E. , (1991)
“Laboratory Methods for Sensory Analysis”, RBAC, Canada.
2. Thomas J.W, (Copy right: 2002), “Product Testing Designs”, (Decision Analyst Inc.)
(Accessed: 2005, August 6)