ISO 29842

FINAL DRAFT
International
Standard
ISO/FDIS 29842
ISO/TC 34/SC 12
Sensory analysis — Methodology —
Secretariat: IRAM
Balanced incomplete block designs
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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
Voting terminates on:
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2024
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
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TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
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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,
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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)
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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.

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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
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