ISO 13301:2002 pdf download

ISO 13301:2002 pdf download.Sensory analysis一Methodology 一
General guidance for measuring odour, flavour and taste detection thresholds by a three-alternative forced-choice (3-AFC) procedure.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards.
ISO 5492:1992, Sensory analysis — Vocabulary
ISO 6658:1985, Sensory analysis — Methodology — General guidance
ISO 8586-1 :1993, Sensory analysis — General guidance for the selection, training and monitoring of assessors — Part 1: Selected assessors
ISO 8586-2:1994, Sensory analysis — General guidance for the selection, training and monitoring of assessors — Part 2: Experts
ISO 8589:1988, Sensory analysis — General guidance for the design of test rooms
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 5492, as well as the following, apply.
stimulus
substance that may or may not cause a sensation, detectable by one or more of the senses, depending on the amount present
3.2
medium
any material used to dissolve, dilute, disperse or sorb a stimulus whose threshold is to be measured
3.3
reference sample
quantity of the medium containing no added stimulus
3.4
test sample
quantity of the medium to which a stimulus has been added at a known concentration
3.5
three-alternative forced-choice (3-AFC) test
test of discrimination in which the assessor is presented with three samples, one of which is a test sample containing a nominated stimulus familiar to the assessor, the other two being references, and where the assessor is instructed to indicate the test sample
3.6
presentation
set of three samples forming a 3-AFC test
3.7
threshold model
model of sensory detection where a stimulus presented on a particular trial is either detected (resulting in a correct response) or is not detected (resulting in a response being made at random)
3.8
signal-detection model
model of sensory detection where a stimulus presented on a particular trial provides some level of evidence of its presence
NOTE The evidence contributes to a decision by the assessor about the presence or absence of the stimulus.
4 Principles
4.1 Experimental procedures
The stimulus is formulated in the medium at a specified concentration and is presented along with a pair of reference samples to the assessor. The assessor is required to select one of the samples as containing the stimulus or having the stimulus at a greater concentration. The assessor must make a selection. It is a requirement of the 3-AFC test that the assessor be able to recognize the stimulus.
Typically the stimulus is dissolved in air or water. It is unlikely that a gas other than air will be used as a gaseous medium in tests with human assessors, but solvents other than water, solutions in water or other solvents, or solids, e.g. foods, can be used as liquid or solid medium to dilute the stimulus as the experiment dictates. It is essential that the medium be homogeneous so that the members of the pair of references are identical, and the same in all presentations.
The stimulus is presented at several concentrations. The presentations are replicated, at each concentration, a sufficient number of times to achieve a desired precision of the threshold and parameters of the mathematical model. The nature of the replications within assessors, across assessors, and combinations of the two are set by the experimental design of the study.
4.2 Data processing
The outcome of a presentation is a binary result — the sample nominated by the assessor is the test sample (a correct selection) or is one of the references (an incorrect selection). The number of correct selections is summed over the number of presentations at each stimulus concentration and forms, along with the total number of presentations and the stimulus concentration, the data to be processed for obtaining the derived statistics. The statistical model is that the number of correct selections at a particular concentration comes from a binomial distribution.
For the 3-AFC test, the threshold is the concentration of the stimulus at which the proportion of correct selections is equal to 2/3, i.e. 50 % above chance. The data, as proportions of correct selections, can simply be inspected and interpolated to derive this point, but a more accurate estimate of the threshold, and its bounds, can be obtained by fitting a mathematical model to the data. A logistic model is used in these guidelines, and the model is fitted by a maximum likelihood procedure, or alternatively, by a least squares procedure. The fitting estimates the two parameters of the model, one a location parameter, the other a shape parameter. The former locates the fitted curve on the stimulus continuum, the latter determines the steepness of the curve. The fitted curve allows estimates of proportions of detection other than 50 % to be derived.
The simDlest model to fit is one in which the distribution of DroDortion of correct selections comes from a sinale.