The power of the "A"-"Not A" method

The "A "- "Not A" method is a rating method with two categories. It is ofte n treated as a discrimination method. Unlike forced choice procedures, the Thurstonian model for this method involves a choice criterion. In statistic al tests, it is treated as a comparison of two proportions. In this paper, the power for hypothesis tests involving the monadic and replicated monadic "A "- "Not A" method is discussed. The power functions and the sample size s needed for 80% power are given based on Thurstone's delta. Designs with e qual and unequal allocations for A and A(-)(Not A) samples are considered. The power of the method is also compared with that of four forced choice me thods under the assumption that the perceptual variance is identical among methods. The comparison shows that, in general, the power for the five meth ods ranks from high to low: the 3-AFC, 2-AFC, "A "- "Not A", triangular and duo-trio. The comparison also shows that, based on the same number of pane lists and/or the same sample size for the A and A- samples for the methods, if the panelists are not too discrepant and the choice criterion in the "A "- "Not A" method is not too strict or too lax, the power of the "A "- "No t A" method is very close to that of the 2-AFC method.