Subject:Psychophysical measurement technique - PEST?From:Peter Marvit <marvit(at)CATTELL.PSYCH.UPENN.EDU>Date:Sun, 28 Feb 1993 15:29:22 ESTHaving successfully used the up/down technique to get estimates of psychometric functions for different % correct levels in various psychoacoustic tasks (see Levitt, 1970, Journal of the Acoustical Sociery of America, V49 #2, pp467), it was suggested I look into PEST (Parameter Estimation by Sequentual Testing) as a more efficient adaptive procedure. The original reference is Taylor & Creelman, 1967, JASA, V41 #4, pp782f. My (current) application? I want to find difference limens at 75% correct in psychiatric patient populations and so want to do the measurement with the least number of trials possible. While I think I understand the basic concepts of the 1967 PEST paper, I do *not* understand how to determine the parameters of the algorithm for a given "probability of positive response" (P sub t in the paper). I also don't fully understand the meaning of W. The paper references a book by Wald (1947, "Sequential Analysis") which I admit not to have seen yet. Would this shed some illumination? So, my questions: Can someone offer any of 1) a pointer to a more recent paper describing PEST and its theoretic efficiencies (and/or implementations), 2) code fragments illustrating an actual computer implementation, or 3) an intuitive explanation of the variables and their effects in the PEST procedure? Many thanks in advance, Peter "maybe I need RAID?" Marvit : Peter Marvit <marvit(at)cattell.psych.upenn.edu> : : Psychology Department, University of Pennsylvania : : 3815 Walnut St., Philadelphia, PA 19104 w:215/898-9208 h:215/387-6433 :

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