ISO 11056:2021 Sensory analysis — Methodology — Magnitude estimation method

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INTERNATIONAL STANDARD ISO 11056:2021

Sensory analysis — Methodology — Magnitude estimation method

1 Scope

This document specifies a method for applying magnitude estimation to the evaluation of sensory attributes. The methodology specified covers the training of assessors, and obtaining magnitude estimations as well as their statistical interpretation.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 3534-1, Statistics — Vocabulary and symbols — Part 1: General statistical terms and terms used in probability

ISO 3534-3, Statistics — Vocabulary and symbols — Part 3: Design of experiments

ISO 4121, Sensory analysis — Guidelines for the use of quantitative response scales

ISO 5492, Sensory analysis — Vocabulary

ISO 6658, Sensory analysis — Methodology — General guidance

ISO 8586, Sensory analysis — General guidelines for the selection, training and monitoring of selected assessors and expert sensory assessors

ISO 8589, Sensory analysis — General guidance for the design of test rooms

3 Terms a nd definiti ons

For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 3534-3, ISO 5492 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at http://www.electropedia.org/

3.1

magnitude estimation

process of assigning values to the intensity of a sensation elicited by a product attribute, or to its hedonic value, so the ratio between the assigned value and the assessor’s perception of the attribute remains the same

3.2

external reference

first sample presented as a reference in a sample series in relation to which all subsequent samples are then assessed

ISO 11056:2021

3.3

internal reference

first sample introduced in a sample series in relation to which all subsequent samples are then assessed, and presented to the assessor as if it was a test sample

3.4

modulus

numerical value assigned to the external reference (3.2), which can be defined by the person conducting the test (fixed modulus) or left to the assessor to choose (non-fixed modulus)

3.5

rescaling

process that consists of multiplying the raw data supplied by each assessor by a factor which reduces the data of all the assessors to a common scale

Note 1 to entry: Adding the logarithm of this factor to the logarithm of the raw data is an equivalent process.

3.6

Steven’s equation psychophysical power function

relationship that is expressed as:

n

RK= S

where

R is the assessor’s response (e.g. perceived intensity);

K is the constant which reconciles the units of measurement used for R and S;

S is the stimulus (concentration of a chemical substance or physical variable);

n is the exponent of the power function and the slope of the regression curve for R and S when they are expressed in logarithmic units.

Note 1 to entry: In practice, Stevens’s equation is generally transformed into natural logarithms:

lnRK=ln +lnSn

4 Principle

Samples are presented successively to assessors, who are requested to record the intensity of an attribute of each sample by complying with the ratio principle.

The values are assigned by referring to the value of the first sample of the series. For this first sample, either each assessor is free to assign a value to it, or the value is fixed by the person conducting the test. The latter case is called “fixed modulus”.

5 General test conditions

For the general test conditions, such as those concerning the facilities, preparation, presentation and coding of samples, International Standards on general methodology shall be followed, in particular ISO 6658 and ISO 8589, as well as those describing the methods using scales and categories, in particular ISO 4121.

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