ISO 29842:2024
(Main)Sensory analysis — Methodology — Balanced incomplete block designs
Sensory analysis — Methodology — Balanced incomplete block designs
This document specifies a method for the application of balanced incomplete block designs to sensory descriptive and hedonic tests. This document is applicable when the number of test samples exceeds the number of evaluations that an assessor can perform reliably in a single session. This document also specifies the fundamental characteristics of balanced incomplete block designs and establishes guidelines for their application in sensory evaluation.
Analyse sensorielle — Méthodologie — Plans de présentation en blocs incomplets équilibrés
Le présent document spécifie une méthode pour l’application de plans de présentation en blocs incomplets équilibrés destinés aux essais sensoriels descriptifs et hédoniques. Le présent document s’applique lorsque le nombre d’échantillons pour essai est supérieur au nombre d’évaluations qu’un sujet peut effectuer de manière fiable au cours d’une seule session. Le présent document spécifie également les caractéristiques fondamentales des plans de présentation en blocs incomplets équilibrés et établit les lignes directrices relatives à leur application dans le cadre de l’évaluation sensorielle.
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International
Standard
ISO 29842
Second edition
Sensory analysis — Methodology —
2024-06
Balanced incomplete block designs
Analyse sensorielle — Méthodologie — Plans de présentation en
blocs incomplets équilibrés
Reference number
© ISO 2024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
ii
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specification of balanced incomplete block designs . 1
5 Data analysis . 2
5.1 General .2
5.2 Analysis of variance for rating data .3
5.3 Friedman's sum rank analysis for rank data .5
6 Application in sensory evaluation. 6
Annex A (informative) Catalogue of incomplete block designs . 7
Annex B (informative) Example of balanced incomplete block design with ratings data .15
Annex C (informative) Example of balanced incomplete block design with rank data . 17
Bibliography . 19
iii
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12,
Sensory analysis.
This second edition cancels and replaces the first edition (ISO 29842:2011), of which it constitutes a minor
revision. It also incorporates the Amendment ISO 29842:2011/Amd.1:2015.
The changes are as follows:
— the corrections of the amendment have been included;
— in Table 2, the formulae in the column “Mean square” have been corrected.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
International Standard ISO 29842:2024(en)
Sensory analysis — Methodology — Balanced incomplete
block designs
1 Scope
This document specifies a method for the application of balanced incomplete block designs to sensory
descriptive and hedonic tests.
This document is applicable when the number of test samples exceeds the number of evaluations that an
assessor can perform reliably in a single session.
This document also specifies the fundamental characteristics of balanced incomplete block designs and
establishes guidelines for their application in sensory evaluation.
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 5492, Sensory analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 5492 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
block design
multi-sample serving protocol in which an assessor evaluates all or a subset of the
samples in a study
3.2
repetition
one occurrence of an experimental design
4 Specification of balanced incomplete block designs
Balanced incomplete block (BIB) designs apply to sensory tests in which the total number of samples
is greater than the number that can be evaluated before sensory and psychological fatigue set in. In BIB
designs, each assessor evaluates only a subset of the total number of samples in a single session.
An example of a BIB design is shown in Table 1.
Table 1 — A BIB design with five samples and 10 block/assessors
Test sample
Block
(assessor)
1 2 3 4 5
1 × × × — —
2 × × — × —
3 × × — — ×
4 × — × × —
5 × — × — ×
6 × — — × ×
7 — × × × —
8 — × × — ×
9 — × — × ×
10 — — × × ×
In a BIB design each assessor evaluates a subset, k, of the total number of samples, t, where k < t. The subset of
samples that an assessor evaluates is selected so that, in a single repetition of the BIB design, every sample is
evaluated an equal number of times and all possible pairs of two samples are evaluated by an equal number
of assessors.
The notation most commonly used in a BIB design is as follows:
— t number of test samples;
— k number of samples evaluated by an assessor in a single session (k < t);
— b total number of blocks (typically, assessors) in one repetition of the BIB design;
— r number of times each test sample is evaluated in one repetition of the BIB design;
— λ number of times each pair of samples is evaluated by the same assessor;
— p number of times the basic BIB design is repeated.
Notationally, each assessor evaluates k of the t samples (k < t). The subset of k samples that an assessor
evaluates is selected so that in a single repetition of the BIB design every sample is evaluated an equal
number of times and all possible pairs of samples are evaluated by an equal number of assessors. The number
of blocks (assessors) required to complete a single repetition of the BIB design is denoted by b. The number
of times each sample is evaluated in a single repetition of the BIB design is denoted by r and the number of
times every pair of two samples is evaluated together is denoted by λ.
The entire BIB design may need to be repeated several times in order to achieve an adequate level of precision
for the study. The number of repetitions of the basic BIB design is denoted by p. The total number of blocks
(typically assessors) is then p*b and the total of evaluations per sample is then p*r. The total number of times
each pair of samples is seen together is p*λ.
The constant values of r and λ for all samples in the BIB design imparts important statistical properties to
data collected from the design. The constant value of r ensures that the mean values of all of the samples are
estimated with equal precision. The constant value of λ ensures that all pair-wise comparisons between any
two samples are equally sensitive.
5 Data analysis
5.1 General
Two types of data can be collected using balanced incomplete block designs. Ratings data, or scores, are
obtained when assessors use a scale to report the perceived intensities of the attributes or impressions they
are evaluating. Rank data are obtained when assessors order the samples from lowest to highest (or vice
versa) relative to the attribute they are evaluating. Different data analysis methods are used for ratings and
rank data.
5.2 Analysis of variance for rating data
Analysis of variance (ANOVA) is used to analyse ratings data obtained from the BIB design. The sources
of variability accounted for in the ANOVA model for the BIB design are the same as those accounted for in
a randomized (complete) block design. In both cases, the total variability is partitioned into the separate
effects of blocks (typically assessors), treatments (typically samples) and errors. Because each assessor
evaluates only a subset of the total number of test samples, more complicated formulae are required to
calculate the ANOVA sum-of-squares for the BIB design than for the randomized (complete) block design.
The sensory analyst shall ensure that the program used to perform the analysis is capable of handling BIB
designs. In many statistical computer packages, the ANOVA procedure applies only to complete designs,
i.e. studies in which every assessor evaluates all of the test samples. For incomplete designs, such as BIB
designs, the general linear model (GLM) procedure or a mixed model procedure is required.
The form of the ANOVA used to analyse BIB data depends on how the design is administered.
Where the experiment is of the form of the example in Table 1, with a single repetition of the design, the
ANOVA table is as shown in Table 2.
Table 2 — ANOVA table for balanced incomplete block design (single repetition)
Source of variation Degrees of freedom Sum of squares Mean square F
(DF) (SS) (MS)
Total ν = t*r – 1 S
T T
Assessors ν = b – 1 S
B B
Samples (adjusted for assessors) ν = t – 1 S MS = S /ν MS /MS
S S S S S S E
Error ν = t*r – t – b + 1 S MS = S /ν
E E E E E
If the F-statistic in Table 2 exceeds the upper-α critical value of an F with the corresponding degrees of
freedom, then the null hypothesis assumption of equivalent mean ratings is rejected. If the F-statistic is
significant, a multiple comparison procedure, such as Fisher's LSD (least significant difference), L, shall be
applied to determine which samples are significantly different from one another. The equation for Fisher's
LSD, L, appropriate for a single repetition of this BIB design is:
2MS
kt()−1
E
Lt=
αν/,2
E
r ()kt−1
where
t, k and r are as defined in Clause 4;
MS is the mean square for error from the ANOVA table;
E
ν is the number of degrees of freedom for error from the ANOVA table;
E
t
is the upper α/2 critical value of Student's t-distribution with ν degrees of freedom.
αν/,2
E
E
The same value of α shall be used for assessing the significance of the F-statistic and in Fisher's LSD, L.
The BIB design shall be repeated p times to achieve an adequate level of precision from the study. If the
total number of blocks is too large for each assessor to evaluate all of them, each of the p*b assessors shall
evaluate only one block of k samples. Within each block, the order in which the k samples are evaluated shall
be done at random. Th
...
Norme
internationale
ISO 29842
Deuxième édition
Analyse sensorielle — Méthodologie
2024-06
— Plans de présentation en blocs
incomplets équilibrés
Sensory analysis — Methodology — Balanced incomplete block
designs
Numéro de référence
DOCUMENT PROTÉGÉ PAR COPYRIGHT
© ISO 2024
Tous droits réservés. Sauf prescription différente ou nécessité dans le contexte de sa mise en œuvre, aucune partie de cette
publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique,
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Publié en Suisse
ii
Sommaire Page
Avant-propos .iv
1 Domaine d’application . 1
2 Références normatives . 1
3 Termes et définitions . 1
4 Spécification des plans de présentation en blocs incomplets équilibrés . 1
5 Analyse des données . 3
5.1 Généralités .3
5.2 Analyse de la variance pour les données de notation .3
5.3 Analyse de la somme des rangs de Friedman pour les données de rang . .5
6 Application dans l’évaluation sensorielle . 6
Annexe A (informative) Catalogue des plans de présentation en blocs incomplets . 7
Annexe B (informative) Exemple de plan de présentation en blocs incomplets équilibrés avec
données de notation .15
Annexe C (informative) Exemple de plan de présentation en blocs incomplets équilibrés avec
données de rang . 17
Bibliographie . 19
iii
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes nationaux
de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est en général
confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude a le droit de faire
partie du comité technique créé à cet effet. Les organisations internationales, gouvernementales et non
gouvernementales, en liaison avec l’ISO participent également aux travaux. L’ISO collabore étroitement avec
la Commission électrotechnique internationale (IEC) en ce qui concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a
été rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2 (voir
www.iso.org/directives).
L’ISO attire l’attention sur le fait que la mise en application du présent document peut entraîner l’utilisation
d’un ou de plusieurs brevets. L’ISO ne prend pas position quant à la preuve, à la validité et à l’applicabilité de
tout droit de brevet revendiqué à cet égard. À la date de publication du présent document, l’ISO n’avait pas
reçu notification qu’un ou plusieurs brevets pouvaient être nécessaires à sa mise en application. Toutefois,
il y a lieu d’avertir les responsables de la mise en application du présent document que des informations
plus récentes sont susceptibles de figurer dans la base de données de brevets, disponible à l’adresse
www.iso.org/brevets. L’ISO ne saurait être tenue pour responsable de ne pas avoir identifié tout ou partie de
tels droits de propriété.
Les appellations commerciales éventuellement mentionnées dans le présent document sont données pour
information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion de
l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles techniques au
commerce (OTC), voir www.iso.org/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 34, Produits alimentaires, sous-comité
SC 12, Analyse sensorielle.
Cette deuxième édition annule et remplace la première édition (ISO 29842:2011), dont elle constitue une
révision mineure. Elle incorpore également l’Amendement l’ISO 29842:2011/Amd.1:2015.
Les modifications sont les suivantes:
— ajout des corrections de l’amendement;
— correction de la formule de la colonne «Carré moyen» dans le Tableau 2.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes se
trouve à l’adresse www.iso.org/fr/members.html.
iv
Norme internationale ISO 29842:2024(fr)
Analyse sensorielle — Méthodologie — Plans de présentation
en blocs incomplets équilibrés
1 Domaine d’application
Le présent document spécifie une méthode pour l’application de plans de présentation en blocs incomplets
équilibrés destinés aux essais sensoriels descriptifs et hédoniques.
Le présent document s’applique lorsque le nombre d’échantillons pour essai est supérieur au nombre
d’évaluations qu’un sujet peut effectuer de manière fiable au cours d’une seule session.
Le présent document spécifie également les caractéristiques fondamentales des plans de présentation
en blocs incomplets équilibrés et établit les lignes directrices relatives à leur application dans le cadre de
l’évaluation sensorielle.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références datées, seule l’édition citée s’applique. Pour
les références non datées, la dernière édition du document de référence s’applique (y compris les éventuels
amendements).
ISO 3534-1, Statistique — Vocabulaire et symboles — Partie 1: Termes statistiques généraux et termes utilisés
en calcul des probabilités
ISO 5492, Analyse sensorielle — Vocabulaire
3 Termes et définitions
Pour les besoins du présent document, les termes et les définitions de l’ISO 3534-1 et de l’ISO 5492 ainsi que
les suivants s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en normalisation,
consultables aux adresses suivantes:
— ISO Online browsing platform: disponible à l’adresse https:// www .iso .org/ obp
— IEC Electropedia: disponible à l’adresse https:// www .electropedia .org/
3.1
plan de présentation en blocs
protocole de présentation de plusieurs échantillons au cours duquel un sujet évalue
dans une étude, l’ensemble des échantillons ou un sous-ensemble d’échantillons
3.2
répétition
occurrence unique d’un plan d’expérience
4 Spécification des plans de présentation en blocs incomplets équilibrés
Les plans de présentation en blocs incomplets équilibrés (BIE) s’appliquent aux essais sensoriels dans
lesquels le nombre total d’échantillons est supérieur au nombre qui peut être évalué avant l’apparition
d’une fatigue sensorielle et psychologique. Dans les plans BIE, chaque sujet évalue un seul sous-ensemble du
nombre total d’échantillons au cours d’une seule session.
Un exemple de plan BIE est présenté dans le Tableau 1.
Tableau 1 — Plan BIE avec cinq échantillons et dix blocs/sujets
Échantillon pour essai
Bloc
(sujet)
1 2 3 4 5
1 × × × — —
2 × × — × —
3 × × — — ×
4 × — × × —
5 × — × — ×
6 × — — × ×
7 — × × × —
8 — × × — ×
9 — × — × ×
10 — — × × ×
Dans un plan BIE, chaque sujet évalue un sous-ensemble, k, du nombre total d’échantillons, t, où k < t.
Le sous-ensemble d’échantillons qu’un sujet évalue est choisi de sorte que dans une seule répétition du plan
BIE, chaque échantillon est évalué le même nombre de fois et toutes les paires possibles de deux échantillons
sont évaluées par un nombre égal de sujets.
Dans un plan BIE, la notation la plus couramment utilisée est la suivante:
— t nombre d’échantillons pour essai;
— k nombre d’échantillons évalués par un sujet au cours d’une seule session (k < t);
— b nombre total de blocs (généralement les sujets) dans une répétition du plan BIE;
— r nombre de fois où chaque échantillon pour essai est évalué dans une répétition du plan BIE;
— λ nombre de fois où chaque paire d’échantillons est évaluée par le même sujet;
— p nombre de fois où le plan BIE de base est répété.
D’un point de vue notationnel, chaque sujet évalue k échantillons parmi t (k < t). Le sous-ensemble
de k échantillons qu’un sujet évalue est choisi de sorte que, dans une seule répétition du plan BIE,
chaque échantillon soit évalué le même nombre de fois et toutes les paires d’échantillons possibles soient
évaluées par un nombre égal de sujets. Le nombre de blocs (sujets) exigés pour réaliser une seule répétition
du plan BIE est désigné par b. Le nombre de fois où chaque échantillon est évalué dans une seule répétition
du plan BIE est désigné par lettre r et le nombre de fois où chaque paire de deux échantillons est évaluée
ensemble est désigné par λ.
Il peut être nécessaire de répéter plusieurs fois l’ensemble du plan BIE afin d’obtenir un niveau de précision
adéquat pour l’étude. Le nombre de répétitions du plan BIE de base est désigné par p. Le nombre total de
blocs (généralement les sujets) est alors p*b et le nombre total d’évaluations par échantillon est alors p*r. Le
nombre total de fois où chaque paire d’échantillons est évaluée ensemble est p*λ.
Les valeurs constantes de r et λ pour tous les échantillons dans le plan BIE confèrent d’importantes
propriétés statistiques aux données collectées d’après le plan. La valeur constante de r garantit que les
valeurs moyennes de tous les échantillons sont estimées avec la même précision. La valeur constante de λ
garantit que toutes les comparaisons par paires entre deux échantillons sont de sensibilité égale.
5 Analyse des données
5.1 Généralités
Deux types de données peuvent être collectés en utilisant les plans de présentation en blocs incomplets
équilibrés. Les données de notation, ou notes, sont obtenues lorsque les sujets utilisent une échelle pour
consigner les intensités perçues des attributs ou impressions qu’ils évaluent. Les données de rang sont
obtenues lorsque les sujets classent les échantillons par ordre croissant (ou décroissant) en fonction de
l’attribut qu’ils évaluent. Différentes méthodes d’analyse des données sont utilisées pour les données de
notation et de rang.
5.2 Analyse de la variance pour les données de notation
L’analyse de la variance (ANOVA) est utilisée pour analyser les données de notation obtenues d’après
le plan BIE. Les sources de variabilité prises en compte dans le modèle ANOVA pour le plan BIE sont les
mêmes que celles utilisées dans un plan de présentation en blocs aléatoires (complets). Dans les deux cas,
la variabilité totale est répartie entre les effets séparés des blocs (généralement les sujets), des traitements
(généralement les échantillons) et des erreurs. Dans le cas du plan BIE, dans la mesure où chaque sujet
n’évalue qu’un sous-ensemble du nombre total d’échantillons pour essai, des formules plus compliquées que
celles du plan de présentation en blocs aléatoires (complets) sont exigées pour calculer la somme des carrés
de l’ANOVA. L’analyste sensoriel doit s’assurer que le programme utilisé pour effectuer l’analyse est capable
de gérer les plans BIE. Dans de nombreux programmes informatiques statistiques, la procédure ANOVA ne
s’applique qu’aux plans en blocs complets, c’est-à-dire aux études dans lesquelles chaque sujet évalue tous
les échantillons pour essai. Pour les plans en blocs incomplets, notamment les plans BIE, le modèle linéaire
généralisé (MLG) ou un modèle mixte est exigé.
La forme de l’ANOVA utilisée pour analyser les données BIE dépend de la façon dont le plan est géré.
Lorsque l’expérience est du type de celle donn
...
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Reference number
ISO/FDIS 29842:2024(en) © ISO 2024
FINAL DRAFT
ISO/FDIS 29842:2024(en)
International
Standard
ISO/FDIS 29842
ISO/TC 34/SC 12
Sensory analysis — Methodology —
Secretariat: IRAM
Balanced incomplete block designs
Voting begins on:
Analyse sensorielle — Méthodologie — Plans de présentation en
blocs incomplets équilibrés
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Published in Switzerland Reference number
ISO/FDIS 29842:2024(en) © ISO 2024
ii
ISO/FDIS 29842:2024(en)
Contents Page
Foreword .iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specification of balanced incomplete block designs . 1
5 Data analysis . 2
5.1 General .2
5.2 Analysis of variance for rating data .3
5.3 Friedman's sum rank analysis for rank data .5
6 Application in sensory evaluation. 6
Annex A (informative) Catalogue of incomplete block designs . 7
Annex B (informative) Example of balanced incomplete block design with ratings data .15
Annex C (informative) Example of balanced incomplete block design with rank data . 17
Bibliography . 19
iii
ISO/FDIS 29842:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34, Food products, Subcommittee SC 12,
Sensory analysis.
This second edition cancels and replaces the first edition (ISO 29842:2011), of which it constitutes a minor
revision. It also incorporates the Amendment ISO 29842:2011/Amd.1:2015.
The changes are as follows:
— the corrections of the amendment have been included;
— the following clarifying sentence has been added in 5.2: “Typically, the assessors who participate in the
study are considered to comprise a random sample from a hypothetical population of similarly trained
and qualified assessors and are, therefore, treated as a random effect in the ANOVA model”;
— in Table 2, the formulae in the column “Mean square” have been corrected.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
FINAL DRAFT International Standard ISO/FDIS 29842:2024(en)
Sensory analysis — Methodology — Balanced incomplete
block designs
1 Scope
This document specifies a method for the application of balanced incomplete block designs to sensory
descriptive and hedonic tests.
This document is applicable when the number of test samples exceeds the number of evaluations that an
assessor can perform reliably in a single session.
This document also specifies the fundamental characteristics of balanced incomplete block designs and
establishes guidelines for their application in sensory evaluation.
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 5492, Sensory analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 3534-1, ISO 5492 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
block design
multi-sample serving protocol in which an assessor evaluates all or a subset of the
samples in a study
3.2
repetition
one occurrence of an experimental design
4 Specification of balanced incomplete block designs
Balanced incomplete block (BIB) designs apply to sensory tests in which the total number of samples
is greater than the number that can be evaluated before sensory and psychological fatigue set in. In BIB
designs, each assessor evaluates only a subset of the total number of samples in a single session.
An example of a BIB design is shown in Table 1.
ISO/FDIS 29842:2024(en)
Table 1 — A BIB design with five samples and 10 block/assessors
Test sample
Block
(assessor)
1 2 3 4 5
1 × × × — —
2 × × — × —
3 × × — — ×
4 × — × × —
5 × — × — ×
6 × — — × ×
7 — × × × —
8 — × × — ×
9 — × — × ×
10 — — × × ×
In a BIB design each assessor evaluates a subset, k, of the total number of samples, t, where k < t. The subset of
samples that an assessor evaluates is selected so that, in a single repetition of the BIB design, every sample is
evaluated an equal number of times and all possible pairs of two samples are evaluated by an equal number
of assessors.
The notation most commonly used in a BIB design is as follows:
— t number of test samples;
— k number of samples evaluated by an assessor in a single session (k < t);
— b total number of blocks (typically, assessors) in one repetition of the BIB design;
— r number of times each test sample is evaluated in one repetition of the BIB design;
— λ number of times each pair of samples is evaluated by the same assessor;
— p number of times the basic BIB design is repeated.
Notationally, each assessor evaluates k of the t samples (k < t). The subset of k samples that an assessor
evaluates is selected so that in a single repetition of the BIB design every sample is evaluated an equal
number of times and all possible pairs of samples are evaluated by an equal number of assessors. The number
of blocks (assessors) required to complete a single repetition of the BIB design is denoted by b. The number
of times each sample is evaluated in a single repetition of the BIB design is denoted by r and the number of
times every pair of two samples is evaluated together is denoted by λ.
The entire BIB design may need to be repeated several times in order to achieve an adequate level of precision
for the study. The number of repetitions of the basic BIB design is denoted by p. The total number of blocks
(typically assessors) is then p*b and the total of evaluations per sample is then p*r. The total number of times
each pair of samples is seen together is p*λ.
The constant values of r and λ for all samples in the BIB design imparts important statistical properties to
data collected from the design. The constant value of r ensures that the mean values of all of the samples are
estimated with equal precision. The constant value of λ ensures that all pair-wise comparisons between any
two samples are equally sensitive.
5 Data analysis
5.1 General
Two types of data can be collected using balanced incomplete block designs. Ratings data, or scores, are
obtained when assessors use a scale to report the perceived intensities of the attributes or impressions they
are evaluating. Rank data are obtained when assessors order the samples from lowest to highest (or vice
ISO/FDIS 29842:2024(en)
versa) relative to the attribute they are evaluating. Different data analysis methods are used for ratings and
rank data.
5.2 Analysis of variance for rating data
Analysis of variance (ANOVA) is used to analyse ratings data obtained from the BIB design. The sources
of variability accounted for in the ANOVA model for the BIB design are the same as those accounted for in
a randomized (complete) block design. In both cases, the total variability is partitioned into the separate
effects of blocks (typically assessors), treatments (typically samples) and errors. Typically, the assessors
who participate in the study are considered to comprise a random sample from a hypothetical population
of similarly trained and qualified assessors and are, therefore, treated as a random effect in the ANOVA
model. Because each assessor evaluates only a subset of the total number of test samples, more complicated
formulae are required to calculate the ANOVA sum-of-squares for the BIB design than for the randomized
(complete) block design. The sensory analyst shall ensure that the program used to perform the analysis is
capable of handling BIB designs. In many statistical computer packages, the ANOVA procedure applies only
to complete designs, i.e. studies in which every assessor evaluates all of the t
...
ISO/FDIS 29842:2023(2)
ISO/TC 34/SC 12
Secretariat: IRAM
Date: 2023-09-212024-03-05
Sensory analysis — Methodology — Balanced incomplete block
designs
Analyse sensorielle — Méthodologie — Plans de présentation en blocs incomplets équilibrés
FDIS stage
ISO/FDIS 29842:2024(en)
© ISO 298422024
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
E-mail: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO/FDIS 29842:2024(en)
Contents
Foreword . iv
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Specification of balanced incomplete block designs . 1
5 Data analysis . 3
5.1 General . 3
5.2 Analysis of variance for rating data . 3
5.3 Friedman's sum rank analysis for rank data . 5
6 Application in sensory evaluation . 6
Annex A (informative) Catalogue of incomplete block designs . 7
Annex B (informative) Example of balanced incomplete block design with ratings data . 16
B.1 Problem and situation . 16
B.2 Test design . 16
B.3 Results . 17
Annex C (informative) Example of balanced incomplete block design with rank data . 19
C.1 Problem and situation . 19
C.2 Test design . 19
C.3 Analysis of results . 19
Bibliography . 21
iii
ISO/FDIS 29842:2024(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documentsdocument should be noted. This document was drafted in accordance with the editorial rules
of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO [had/had not] received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that this
may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 34 food, Food products, Subcommittee SC 12,
sensorySensory analysis.
This second edition cancels and replaces the first edition (ISO 29842:2011), which has been technically
revisedof which it constitutes a minor revision. It also incorporates the Amendment ISO
29842:2011/Amd.1:2015.
The main changes are as follows:
— Thethe corrections of the corresponding Amendment 1 (ISO29842 :2011/AMD 1) are amendment have
been included;
— the following clarifying sentence has been added in 5.2this edition. : “Typically, the assessors who
participate in the study are considered to comprise a random sample from a hypothetical population of
similarly trained and qualified assessors and are, therefore, treated as a random effect in the ANOVA
model”;
— in Table 2, the formulae in the column “Mean square” have been corrected.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
ISO/FDIS 29842:2024(en)
Sensory analysis — Methodology — Balanced incomplete block
designs
1 Scope
This International Standarddocument specifies a method for the application of balanced incomplete block
designs to sensory descriptive and hedonic tests.
This International Standard appliesdocument is applicable when the number of test samples exceeds the
number of evaluations that an assessor can perform reliably in a single session.
This International Standarddocument also specifies the fundamental characteristics of balanced incomplete
block designs and establishes guidelines for their application in sensory evaluation.
2 Normative references
The following referenced documents are indispensable forreferred to in the applicationtext 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 5492, Sensory analysis — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 5492, ISO 3534-1, ISO 5492 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at https://www.electropedia.org/
3.1
block design
multi-sample serving protocol in which an assessor evaluates all or a subset of the samples
in a study
3.2
repetition
one occurrence of an experimental design
4 Specification of balanced incomplete block designs
Balanced incomplete block (BIB) designs apply to sensory tests in which the total number of samples is greater
than the number that can be evaluated before sensory and psychological fatigue set in. In BIB designs, each
assessor evaluates only a subset of the total number of samples in a single session.
ISO/FDIS 29842:2024(en)
An example of a BIB design is shown in Table 1.
Table 1 — A BIB design with five samples and 10 block/assessors
Test sample
Block
(assessor)
1 2 3 4 5
1 × × × — —
2 × × — × —
3 × × — — ×
4 × — × × —
5 × — × — ×
6 × — — × ×
7 — × × × —
8 — × × — ×
9 — × — × ×
10 — — × × ×
In a BIB design each assessor evaluates a subset, k, of the total number of samples, t, where k < t. The subset
of samples that an assessor evaluates is selected so that, in a single repetition of the BIB design, every sample
is evaluated an equal number of times and all possible pairs of two samples are evaluated by an equal number
of assessors.
The notation most commonly used in a BIB design is as follows.:
— t number of test samples;
— k number of samples evaluated by an assessor in a single session (k < t);
— b total number of blocks (typically, assessors) in one repetition of the BIB design;
— r number of times each test sample is evaluated in one repetition of the BIB design;
— λ number of times each pair of samples is evaluated by the same assessor;
— p number of times the basic BIB design is repeated.
Notationally, each assessor evaluates k of the t samples (k < t). The subset of k samples that an assessor
evaluates is selected so that in a single repetition of the BIB design every sample is evaluated an equal number
of times and all possible pairs of samples are evaluated by an equal number of assessors. The number of blocks
(assessors) required to complete a single repetition of the BIB design is denoted by b. The number of times
each sample is evaluated in a single repetition of the BIB design is denoted by r and the number of times every
pair of two samples is evaluated together is denoted by λ.
The entire BIB design may need to be repeated several times in order to achieve an adequate level of precision
for the study. The number of repetitions of the basic BIB design is denoted by p. The total number of blocks
(typically assessors) is then p*b and the total of evaluations per sample is then p*r. The total number of times
each pair of samples is seen together is p*λ.
ISO/FDIS 29842:2024(en)
The constant values of r and λ for all samples in the BIB design imparts important statistical properties to data
collected from the design. The constant value of r ensures that the mean values of all of the samples are
estimated with equal precision. The constant value of λ ensures that all pair-wise comparisons between any
two samples are equally sensitive.
5 Data analysis
5.1 General
Two types of data can be collected using balanced incomplete block designs. Ratings data, or scores, are
obtained when assessors use a scale to report the perceived intensities of the attributes or impressions they
are evaluating. Rank data are obtained when assessors order the samples from lowest to highest (or vice
versa) relative to the attribute they are evaluating. Different data analysis methods are used for ratings and
rank data.
5.2 Analysis of variance for rating data
Analysis of variance (ANOVA) is used to analyse ratings data obtained from the BIB design. The sources of
variability accounted for in the ANOVA model for the BIB design are the same as those accounted for in a
randomized (complete) block design. In both cases, the total variability is partitioned into the separate effects
of blocks (typically assessors), treatments (typically samples) and errors. Typically, the assessors who
participate in the study are considered to comprise a random sample from a hypothetical population of
similarly trained and qualified assessors and are, therefore, treated as a random effect in the ANOVA model.
Because each assessor evaluates only a subset of the total number of test samples, more complicated formulae
are required to calculate the ANOVA sum-of-squares for the BIB design than for the randomized (complete)
block design. The sensory analyst shall ensure that the program used to perform the analysis is capable of
handling BIB designs. In many statistical computer packages, the ANOVA procedure applies only to complete
designs, i.e. studies in which every assessor evaluates all of the test samples. For incomplete designs, such as
BIB designs, the general linear model (GLM) procedure or a mixed model procedure is required.
The form of the ANOVA used to analyse BIB data depends on how the d
...
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