stringent test and the low number of discriminators indicate
that the wines compared in these tests were not perceptually
different to this population of consumers. It is
suggested that when the proportion of discriminators is
25% or less, the effect size, in this case the difference in
the sensory properties of the wines due to closure difference,
is considered small (Schlich 1993).
The ability of participants to discriminate among the
wines with different closures was further examined by
comparing difference test results for consumers who reported
drinking wine more frequently, 2 to 3 times a month
or more (frequent) with those who drink wine less frequently,
once a month or less (infrequent). Results indicate
no difference between frequent and infrequent wine
consumers in their ability to detect differences between
the wine samples bottled with the different closures
(Table 4). The power of the test was recalculated post-hoc
for the comparisons between population subsets. For all
comparisons, the calculated power of the test was 90%
with the chance-adjusted percent of correct, or proportion
of discriminators equal to 20% for most comparisons, 30%
for Merlot screwcap versus natural cork and 40% for
Chardonnay and Merlot synthetic versus screwcap. The
higher calculated proportion of discriminators is most
likely due to a relatively lower number of participants in
these subsets, 14 and 22.