Be your own placebo: A double paired preference test approach for establishing expected frequencies

Paired preference tests were performed using plain salted and lemon flavored potato chips. In some cases, identical chips were tested to determine the effects of the experimental situation per se (placebo condition). In other cases, different chips were tested and this allowed measurement of preference, accompanied by the effects of the experimental situation (test condition). Comparison between the two, allowed a measure of preference. A total of 1100 consumers were tested in a variety of experimental conditions. In one condition, a single pair of identical chips was tested while in a different condition, two pairs of chips, one identical, one different, were tested; this allowed both related samples and independent samples designs. All possible combinations of the two orders of pairs (same vs different) and the four orders of tasting within the pairs were tested. Whether the placebo condition was tested first or second appeared to have little effect. Chi-squared was used to determine whether the preference results were significantly different from a ‘no preference’ situation and d′ was used to give a measure of the degree of preference for one product or another. Within-subjects and between-subjects analyses gave the same results. The placebo condition allowed the detection in the test condition of significant preferences as well as the presence of two equally balanced preference groups. The placebo condition also had the potential to be used as a screening tool.