ASTM_E_1432_-_04_2011.pdf

Designation:E143204(Reapproved 2011)Standard Practice forDefining and Calculating Individual and Group SensoryThresholds from Forced-Choice Data Sets ofIntermediate Size1This standard is issued under the fixed designation E1432;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe purpose of this practice is to determine individual sensory thresholds for odor,taste,and othermodalities and,when appropriate,calculate group thresholds.The practice takes as its starting pointany sensory threshold data set of more than 100 presentations,collected by a forced-choice procedure.The usual procedure is the Three-Alternative Forced-Choice(3-AFC)(see ISO 13301),as exemplifiedby Dynamic Triangle Olfactometry.Asimilar practice,Practice E679,utilizes limited-size data sets of50 to 100 3-AFC presentations,and is suitable as a rapid method to approximate group thresholds.Collection of the data is not a part of this practice.The data are assumed to be valid;for example,it is assumed that the stimulus is defined properly,that each subject has been fully trained to recognizethe stimulus and did indeed perceive it when it was present above his or her momentary threshold,andthat the quality of dilution medium did not vary.It is recognized that precise threshold values for a given substance do not exist in the same sensethat values of vapor pressure exist.Apanelists ability to detect a stimulus varies as a result of randomvariations in factors such as alertness,attention,fatigue,events at the molecular level,health status,etc.,the effects of which can usually be described in terms of a probability function.At lowconcentrations of an odorant or tastant,the probability of detection by a given individual is typically0.0 and at high concentrations it is 1.0,and there is a range of concentrations in which the probabilityof detection is between these limits.By definition,the threshold is the concentration for which theprobability of detection of the stimulus is 0.5(that is,50%above chance,by a given individual,underthe conditions of the test).Thresholds may be determined(1)for an individual(or for individuals one by one),and(2)for agroup(panel).While the determination of an individual threshold is a definable task,carefulconsideration of the composition of the group is necessary to ensure the determined thresholdrepresents the group of interest.There is a large degree of random error associated with estimating the probability of detection fromless than approximately 500 3-AFC presentations.The reliability of the results can be increasedgreatly by enlarging the panel and by replicating the tests.1.Scope1.1 The definitions and procedures of this practice apply tothe calculation of individual thresholds for any stimulus in anymedium,from data sets of intermediate size,that is,consistingof more than 20 to 40 3-AFC presentations per individual.Agroup threshold may be calculated using 5 to 15 individualthresholds.1.2 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1This practice is under the jurisdiction of ASTM Committee E18 on SensoryEvaluation and is the direct responsibility of Subcommittee E18.04 on Fundamen-tals of Sensory.Current edition approved Aug.1,2011.Published August 2011.Originallyapproved in 1991.Last previous edition approved in 2004 as E143204.DOI:10.1520/E1432-04R11.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 2.Principles2.1 The 3-AFC procedure is one of the set of n-AFCprocedures,any of which could be used,in principle,for themeasurement of sensory thresholds,as could the duo-trio,thetriangular,and the two-out-of-five procedures.2.2 For calculation of the threshold of one individual,thispractice requires data sets taken at five or more concentrationscale steps,typically six or seven steps,with each step differingfrom the previous step by a factor usually between 2 and 4,typically 3.0.The practice presupposes that the range ofconcentrations has been selected by pretesting,in order toensure that the individuals threshold falls neither outside nornear the ends of the range,but well within it.At eachconcentration step,the individual must be tested several times,typically five or more times.2.3 Individual thresholds,as determined in 2.2,may be usedfor calculation of a group(or panel)threshold.The size andcomposition of the panel(usually 5 to 15 members,preferablymore)is determined according to the purpose for which thethreshold is required and the limitations of the testing situation(se