1、Designation: E 1432 04Standard Practice forDefining and Calculating Individual and Group SensoryThresholds from Forced-Choice Data Sets ofIntermediate Size1This standard is issued under the fixed designation E 1432; the number immediately following the designation indicates the year oforiginal adopt
2、ion or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.INTRODUCTIONThe purpose of this practice is to determine individual sensory threshol
3、ds 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),
4、 as exemplified by DynamicTriangle Olfactometry. A similar practice, Practice E 679, utilizes limited-size data sets of 50 to 1003-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 va
5、lid; 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 preci
6、se threshold values for a given substance do not exist in the same sensethat values of vapor pressure exist. A panelists 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 effect
7、s 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
8、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 o
9、ne), 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 estima
10、ting 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 threshol
11、ds 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, a
12、ssociated 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 of Materials
13、and Products and is the direct responsibility of Subcom-mittee E18.04 on Fundamentals of Sensory.Current edition approved April 1, 2004. Published April 2004. Originallyapproved in 1991. Last previous edition approved in 1997 as E 143291 (1997).1Copyright ASTM International, 100 Barr Harbor Drive, P
14、O Box C700, West Conshohocken, PA 19428-2959, United States.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
15、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 ofco
16、ncentrations 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 de
17、termined 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(see 7.2).2.4 Pooling of t
18、he data sets from panel members to producea single step calculation of the panel threshold is not permitted.3. Referenced Documents3.1 ASTM Standards:2E 122 Practice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for Charac-teristic of a Lot or ProcessE 679 Pra
19、ctice for Determination of Odor and Taste Thresh-olds By a Forced-Choice Ascending Concentration SeriesMethod of Limits3.2 CEN Standard:3EN 13725 Air QualityDetermination of Odour Concen-tration Using Dynamic Dilution Olfactometry3.3 ISO Standard:4ISO 13301 Sensory AnalysisMethodologyGeneralguidance
20、 for Measuring Odour, Flavour, and Taste Detec-tion Thresholds by a Three Alternative Forced Choice(3-AFC) Procedure4. Terminology4.1 Definitions of Terms Specific to This Standard:4.1.1 Three-Alternative Forced-Choice (3-AFC) testprocedurea test presentation used in many threshold tests.For example
21、, in odor testing by Dynamic Triangle Olfactom-etry, the panelist is presented with three gas streams, only oneof which contains the diluted odorant, while the other twocontain odorless carrier gas. The panelist must indicate the onecontaining the added substance. (The 3-AFC procedure isdifferent fr
22、om the classical Triangle test, in which either one ortwo of the three samples may contain the added substance.)4.1.2 modelan abstract or concrete analogy, usually math-ematical, which represents in a useful way the functionalelements of a system or process. In short, the experimenterstheory of what
23、 is guiding the results observed.4.1.3 statistical modela model assuming that the principalfactor causing the results to deviate from the true value is arandom error process. This can usually be described in terms ofa probability function, for example, a bell-shaped curve,symmetrical or skewed. Erro
24、rs are binomially distributed in the3-AFC test procedure.4.1.4 threshold, detectionthe intensity of the stimulus thathas a probability of 0.5 of being detected under the conditionsof the test. The probability of detection at any intensity is nota fixed attribute of the observer, but rather a value w
25、hichassumes that sensitivity varies as a result of random fluctuationin factors such as alertness, attention, fatigue, and events at themolecular level, the effects of which can be modeled by aprobability function.4.1.5 individual thresholda threshold based on a series ofjudgments by a single paneli
26、st.4.1.6 group thresholdthe average, median, geometricmean or other agreed measure (or an experimentally deter-mined measure) of central tendency of the individual thresh-olds of the members of a group (panel). The meaning andsignificance of the term depends on what the group is selectedto represent
27、 (see 7.2.2).4.1.7 scale step factorfor a scale of dilutions presented toa panel, the factor by which each step differs from adjacentsteps.4.1.8 dilution factorthe following applies to flow olfacto-metry: If F1represents the flow of odorless gas which serves todilute the flow of odorant, F2, the dil
28、ution factor, Z, is given by:Z 5F11 F2F2(1)where Z is dimensionless. F1and F2may be expressed, bothin units of mass, or (preferably) both in units of volume; thereport should state which. The term Z50represents the dilutionfactor to threshold. Alternate terminology in use is as follows:dilution-to-t
29、hreshold ratio (D/T or D-T); odor unit (OU); andeffective dose (ED).5. Summary of Practice5.1 From a data set according to 2.2, calculate the thresholdfor one individual graphically or by linear regression accordingto 5.2, or by using a model fitting computer program accordingto 5.3.5.2 Obtain the t
30、hreshold in 5.1 by first calculating theproportion correct above chance for each concentration step.This is accomplished by deducting, from the proportion ofcorrect choices, the proportion that would have been selectedby chance in the absence of the stimulus (see 8.1.2). Then, foreach individual cal
31、culate that concentration which has aprobability of 0.5 of being detected under the conditions of thetest. This is the individual threshold.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volum
32、e information, refer to the standards Document Summary page onthe ASTM website.3Available from British Standards Institute (BSI), 389 Chiswick High Rd.,London W4 4AL, U.K.4Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036.E14320425.3 Alternativ
33、ely obtain the threshold in 5.1 directly fromthe proportion of correct choices by non-linear regression usinga computer program, as described in 8.2.2.5.4 Always report the individual thresholds of the panelists.Depending on the purpose for which a threshold is required(see 7.2), and on the distribu
34、tion found, a group threshold maybe calculated as the arithmetic or geometric mean, the median,or another measure of central tendency, or it may be concludedthat no group threshold can be calculated (see 7.4).6. Significance and Use6.1 Sensory thresholds are used to determine the potential ofsubstan
35、ces at low concentrations to impart odor, taste, skinfeel,etc. to some form of matter.6.2 Thresholds are used, for example, in setting limits in airpollution, in noise abatement, in water treatment, and in foodsystems.6.3 Thresholds are used to characterize and compare thesensitivity of individuals
36、or groups to given stimuli, forexample, in medicine, ethnic studies, and the study of animalspecies.7. Panel Size and Composition Versus Purpose of Test7.1 Panel Size and CompositionPanel variables should bechosen as a function of the purpose for which the resultingthreshold is needed. The important
37、 panel variables are asfollows:7.1.1 Number of tests per panelist,7.1.2 Number of panelists,7.1.3 Selection of panelists to represent a given population,and7.1.4 Degree of training.7.2 Purpose of TestIt is useful to distinguish the followingthree categories:7.2.1 Comparing an Individuals Threshold W
38、ith a Litera-ture ValueThe test may be conducted, for example, todiagnose anosmia or ageusia, or to study sensitivity to pain,noise, or odor. This is the simplest category requiring aminimum of 20 to 40 3-AFC presentations to the individual inquestion (see 2.2). A number of training sessions may ber
39、equired to establish the range of concentrations that will beused and to make certain that the individual is fully familiarwith the stimulus to be detected as well as the mechanics of thetest.7.2.2 A Population Threshold is Required, for example, theodor threshold of a population exposed to a given
40、pollutant, orthe flavor threshold of consumers of a beverage for a givencontaminant. In this case, recourse must be had to the rules ofsampling from a population (see Ref (1)5and Practice E 122),which require the following:(1) That the population be accurately defined and delim-ited,(2) That the sam
41、ple drawn be truly random, that is, thatevery member of the population has a known chance of beingselected, and(3) That knowledge of the degree of variation occurringwithin the population exists or can be acquired in the course offormulating the plan of sampling.7.2.2.1 In practice, the cost and ava
42、ilability of panelistsplaces serious limitations on the degree to which populationfactors affecting thresholds, for example, age groups, gender,ethnic origin, well versus ill, smoker versus nonsmoker, trainedversus casual observers, etc., can be covered. The experimenteris typically limited to panel
43、s of 5 to 15, with each receiving 20to 40 3-AFC presentations, for a total of 100 to 600 presenta-tions. If the resulting thresholds are to have validity for thepopulation, the experimenter should include the followingsteps:(1) Calculate and tabulate the thresholds for each indi-vidual;(2) Repeat th
44、e test for those individuals (outliers) fallingwell beyond the range of the rest of the panel;(3) For any individuals whose threshold at first did not fallwell within the range of samples presented to them, adjust therange and repeat the test; and(4) If needed to obtain a desired level of precision,
45、 repeatthe test series with a second or third panel sampled from thesame population of interest.7.2.2.2 Thresholds vary with age, and one approach to ageneralizable population value is to adjust thresholds obtainedat various ages to an estimate for healthy 20-year-olds, usingAmoores finding (2) that
46、 between the ages of 20 and 65, odorthreshold concentrations double for approximately each 22years of age.7.2.3 The Distribution of Thresholds in the Population isRequired, for example, to determine what proportion of thepopulation is affected by a given level of a pollutant, or,conversely, to deter
47、mine which concentrations of a pollutantwill affect a given percent of a population. The requirementsfor testing are the same as in 7.2.2, except that it is even moreimportant to cover the range well, for example, to repeat thetests for those individuals whose thresholds fall in thinlypopulated part
48、s of the panel range. Consideration should begiven to increasing the number of presentations per concentra-tion from 5-7 to 7-10 for such panel members. If the individualthresholds are plotted as in Fig. 1, any sector requiring studywill be apparent from the graph.7.3 Trained Versus Casual Assessors
49、Thresholds shouldnormally be determined for assessors trained by repeatedexposure to detect the stimulus in question whenever it ispresent; however, if the threshold sought is that of a casualobserver (for example, for a warning agent in household gas),naive panelists and mild distraction (for example, noise) maybe used (see Ref. (3).7.4 Choice of the Measure of Central TendencyThe reportshould contain a table or graph providing the individualthresholds of each observer. If a group threshold is required,the measure of central tendency chosen should be that whichbe
