SIST EN ISO 20685:2006
(Main)3-D scanning methodologies for internationally compatible anthropometric databases (ISO 20685:2005)
3-D scanning methodologies for internationally compatible anthropometric databases (ISO 20685:2005)
This International Standard addresses protocols for the use of 3-D surface-scanning systems in the acquisition of human body shape data and measurements defined in ISO 7250 that can be extracted from 3-D scans. It does not apply to instruments that measure the location and/or motion of individual landmarks. While mainly concerned with whole-body scanners, it is also applicable to body-segment scanners (head scanners, hand scanners, foot scanners). The intended audience is those who use 3-D scanners to create 1-D anthropometric databases and the users of 1-D anthropometric data from 3-D scanners. Although not necessarily aimed at the designers and manufacturers of those systems, scanner designers and manufacturers will find it useful in meeting the needs of clients who build and use 1-D anthropometric databases.
3D-Scanverfahren für international kompatible anthropometrische Datenbanken (ISO 20685:2005)
iese Internationale Norm legt Verfahren für die Anwendung von 3D Oberflächenscansystemen für die Gewinnung von Daten zur Form des menschlichen Körpers und für in ISO 7250 festgelegte Messungen fest, die aus 3D Scanns gewonnen werden können.
Obwohl die Internationale Norm überwiegend auf Ganzkörperscanner bezogen ist, ist sie auch auf Körperteilscanner (Kopfscanner, Handscanner, Fußscanner) anwendbar.
Sie ist nicht auf Geräte anwendbar, die den Ort und/oder die Bewegung einzelner Markierungen messen.
3D Scanner werden eingesetzt, um anthropometrische 1D Datenbanken zu erstellen, und anthropometrischen 1D Daten zu verwenden, die mit 3D Scannern gewonnen wurden. Obwohl dies nicht notwendigerweise die Personen sind, die die Systeme konstruieren und herstellen, werden Konstrukteure und Hersteller von Scannern diese nützlich finden, um die Bedürfnisse ihrer Kunden zu erfüllen, die anthropometrische 1D Datenbanken erstellen und anwenden.
Méthodologies d'exploration tridimensionnelles pour les bases de données anthropométriques compatibles au plan international (ISO 20685:2005)
Postopki 3D-skeniranja za mednarodno združljive baze antropometrijskih podatkov (ISO 20685:2005)
General Information
Relations
Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 20685:2006
01-marec-2006
Postopki 3D-skeniranja za mednarodno združljive baze antropometrijskih
podatkov (ISO 20685:2005)
3-D scanning methodologies for internationally compatible anthropometric databases
(ISO 20685:2005)
3D-Scanverfahren für international kompatible anthropometrische Datenbanken (ISO
20685:2005)
Méthodologies d'exploration tridimensionnelles pour les bases de données
anthropométriques compatibles au plan international (ISO 20685:2005)
Ta slovenski standard je istoveten z: EN ISO 20685:2005
ICS:
13.180 Ergonomija Ergonomics
SIST EN ISO 20685:2006 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 20685:2006
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SIST EN ISO 20685:2006
EUROPEAN STANDARD
EN ISO 20685
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2005
ICS 13.180
English Version
3-D scanning methodologies for internationally compatible
anthropometric databases (ISO 20685:2005)
Méthodologies d'exploration tridimensionnelles pour les 3D-Scanverfahren für international kompatible
bases de données anthropométriques compatibles au plan anthropometrische Datenbanken (ISO 20685:2005)
international (ISO 20685:2005)
This European Standard was approved by CEN on 12 September 2005.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Central Secretariat or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2005 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 20685:2005: E
worldwide for CEN national Members.
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SIST EN ISO 20685:2006
EN ISO 20685:2005 (E)
Foreword
This document (EN ISO 20685:2005) has been prepared by Technical Committee ISO/TC 159
"Ergonomics" in collaboration with Technical Committee CEN/TC 122 "Ergonomics", the
secretariat of which is held by DIN.
This European Standard shall be given the status of a national standard, either by publication of
an identical text or by endorsement, at the latest by May 2006, and conflicting national standards
shall be withdrawn at the latest by May 2006.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of
the following countries are bound to implement this European Standard: Austria, Belgium,
Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary,
Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland,
Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Endorsement notice
The text of ISO 20685:2005 has been approved by CEN as EN ISO 20685:2005 without any
modifications.
2
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SIST EN ISO 20685:2006
INTERNATIONAL ISO
STANDARD 20685
First edition
2005-11-01
3-D scanning methodologies for
internationally compatible
anthropometric databases
Méthodologies d'exploration tridimensionnelles pour les bases de
données anthropométriques compatibles au plan international
Reference number
ISO 20685:2005(E)
©
ISO 2005
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
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ii © ISO 2005 – All rights reserved
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Accuracy of extracted measurements. 5
5 Research designs for establishing accuracy of body dimensions extracted from scanners . 8
6 Method for estimating the number of subjects needed. 9
Annex A (informative) Methods for reducing error in 3-D scanning . 11
Bibliography . 20
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 20685 was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 3,
Anthropometry and biomechanics.
iv © ISO 2005 – All rights reserved
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Introduction
Anthropometric measures are key to many International Standards. These measures can be gathered using a
variety of instruments. An instrument with relatively new application to anthropometry is a three-dimensional
(3-D) scanner. 3-D scanners generate a 3-D point cloud of the outside of the human body that can be used for
clothing and automotive design, engineering and medical applications. There are currently no standardized
methods for using 3-D point clouds in the design process. As a result, many users extract one-dimensional
(1-D) data from 3-D point clouds. This standard concerns the application of 3-D scanners to the collection of
one-dimensional anthropometric data for use in design.
There are a number of different fundamental technologies that underlie commercially available systems.
These include stereophotogrammetry, ultrasound and light (laser light, white light and infrared), among others.
Further, the software that is available to process data from the scan varies in its methods. Additionally,
software to extract dimensions similar to traditional dimensions varies markedly in features and capabilities.
As a result of differences in fundamental technology, hardware and software, extracted measurements from
several different systems can be markedly different for the same individual. Since 3-D scanning can be used
to gather measurements, such as lengths and circumferences, it was important to develop an International
Standard that allows users of such systems to judge whether the 3-D system is adequate for these needs.
The intent of ISO 20685 is to ensure comparability of body measurements as specified by ISO 7250 but
measured with the aid of 3-D body scanners rather than with traditional anthropometric instruments such as
tape measures and callipers. It is further intended that by conformance with this International Standard any
data extracted from scans will be suitable for inclusion in international databases such as those described in
ISO 15535.
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SIST EN ISO 20685:2006
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SIST EN ISO 20685:2006
INTERNATIONAL STANDARD ISO 20685:2005(E)
3-D scanning methodologies for internationally compatible
anthropometric databases
1 Scope
This International Standard addresses protocols for the use of 3-D surface-scanning systems in the
acquisition of human body shape data and measurements defined in ISO 7250 that can be extracted from 3-D
scans. It does not apply to instruments that measure the location and/or motion of individual landmarks.
While mainly concerned with whole-body scanners, it is also applicable to body-segment scanners (head
scanners, hand scanners, foot scanners).
The intended audience is those who use 3-D scanners to create 1-D anthropometric databases and the users
of 1-D anthropometric data from 3-D scanners. Although not necessarily aimed at the designers and
manufacturers of those systems, scanner designers and manufacturers will find it useful in meeting the needs
of clients who build and use 1-D anthropometric databases.
2 Normative references
The following referenced documents are indispensable for the application 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 7250:1996, Basic human body measurements for technological design
ISO 15535: 2003, General requirements for establishing anthropometric databases
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE In the case of definitions of terms for skeletal landmarks, when there is a separate term for the skin overlying
the landmark and another for the landmark itself, the skin landmark term is used. Where there is no separate term, the
skeletal term is used and assumed to refer to the skin overlying the landmark.
3.1
three-dimensional
3-D
pertaining to the use of three orthogonal scales on which the three coordinates, x, y and z, can be measured to
give the precise position of any relevant anatomical point in the considered space
NOTE Many anthropometric distances can be calculated from the coordinates of anatomical landmarks. Some
additional points may be necessary to obtain circumferences.
3.2
3-D body scanner
hardware and software system that creates digital data representing a human form, or parts thereof, in three
dimensions
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
3.3
3-D processing software
operating system, user interface, programs, algorithms and instructions associated with a 3-D scanning
system
3.4
3-D scanner hardware
physical components of a 3-D scanner and any associated computer(s)
3.5
accuracy
extent to which the measured value approximates a true value
NOTE Since it is difficult to trace the accuracy of complex hardware and software systems to recognized ISO sources,
for the purposes of this International Standard true value is taken to mean the measured value obtained by a skilled
anthropometrist using traditional instruments such as tape and calliper.
3.6
acromion
most lateral point of the lateral edge of the spine (acromial process) of the scapula
[ISO 7250:1996, 2.2.1]
3.7
anatomical landmark
clearly defined point on the body that can be used for defining anthropometric measurements
3.8
anterior superior iliac spine
most downward-directed point of the iliac crest
NOTE Adapted from ISO 7250:1996, 4.1.6.
3.9
anthropometric database
collection of individual body measurements (anthropometric data) and background information (demographic
data) recorded on a group of people (the sample)
[ISO 15535:2003, 3.8]
3.10
cervicale
superior tip of the prominent bone at the base of the back of the neck (spinous process of the seventh cervical
vertebra)
NOTE Adapted from ISO 7250:1996, 2.2.5.
3.11
crotch level
distal part of the inferior ramus of the pubic bone on a standing subject
NOTE It is typically marked using the top of a horizontal straightedge.
3.12
Frankfurt plane
standard horizontal plane at the level of tragion and left infraorbitale when the midsagittal plane of the head is
held vertically
NOTE Adapted from ISO 7250:1996, 2.2.8.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
3.13
glabella
most anterior point of the forehead between the browridges in the midsagittal plane
[ISO 7250:1996, 2.2.9]
3.14
iliocristale
most lateral palpable point of the iliac crest of the pelvis
3.15
infraorbitale
lowest point on the anterior border of the bony eye socket
3.16
lateral malleolus
most lateral point of the right lateral malleolus (outside ankle bone)
3.17
lowest rib
inferior point of the bottom of the rib cage
3.18
menton
lowest point of the tip of the chin in the midsagittal plane
NOTE Adapted from ISO 7250:1996, 2.2.16.
3.19
mesosternale
point on the union of the third and fourth sternebrae
[ISO 7250:1996, 2.2.17]
3.20
nipple
centre of the nipple
3.21
opisthocranion
most posterior point of the head in the midsagittal plane, when the head is held in the Frankfurt plane
3.22
point cloud
collection of 3-D points in space referenced by their coordinate values
NOTE A point cloud constitutes the raw data from a 3-D scanner and needs to be translated to a human axis system.
3.23
radial styloid
protuberance of the radius at the wrist
NOTE Adapted from ISO 7250:1996, definition 2.2.26.
3.24
repeatability
extent to which the values of a variable measured twice on the same subject are the same
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
3.25
sellion
point of greatest indentation of the nasal root depression
3.26
stylion
distal point of the radial styloid
NOTE Adapted from ISO 7250:1996, definition 2.2.26.
3.27
suprapatella
superior point of the patella (kneecap)
3.28
thyroid cartilage
prominent cartilage on the anterior surface of the neck
[ISO 7250:1996, 2.2.28]
3.29
tibiale
point at the upper inside (medial) edge of the proximal end of the tibial bone of the lower leg
[ISO 7250:1996, 2.2.29]
3.30
top of head
highest point of the head with the head oriented in the Frankfurt plane
3.31
tragion
notch just above the tragus
NOTE Adapted from ISO 7250:1996, definition 2.2.30.
3.32
tragus
small cartilaginous flap in front of the ear hole
NOTE Adapted from ISO 7250:1996, definition 2.2.30.
3.33
ulnar stylion
most distal point on the ulnar styloid
NOTE Adapted from ISO 7250:1996, definition 2.2.26.
3.34
ulnar styloid
protuberance of the ulna at the wrist
NOTE Adapted from ISO 7250:1996, definition 2.2.26.
3.35
vertical plane
geometric plane tangent to a point on the body and orthogonal to the mid-sagittal plane
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
3.36
x, y, z coordinate system
axis system
system for measuring the body with respect to the standing or sitting human where X refers to the fore-and-aft
direction (the sagittal axis), Y refers to the side-to-side direction (the transverse axis) and Z refers to the
top-to-bottom direction (the longitudinal axis)
See Figure 1.
NOTE Researchers establish their own origin for the axis system, convenient to their research, while keeping the
direction of the axes as indicated and reporting the origin in the data base and any publications.
Figure 1 — x, y, z coordinate system
4 Accuracy of extracted measurements
4.1 Selection of extracted measurements
In order to use data from 3-D scanners in internationally compatible databases, dimensions should be drawn
from ISO 7250. However, not all of those measurements are well suited to extraction from 3-D scanned
images. In particular, the resolution from whole-body scanners might not be sufficient to allow accurate
extraction of measurements from smaller body parts such as the hand. Tables 1 to 3 give measurements
according to the type of scanner most likely to produce the best results. The numbers indicate the
measurement number in ISO 7250.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Table 1 — ISO 7250 measurements by whole-body scanner
Dimension ISO 7250:1996 Position
Stature 4.1.2 B
Eye height 4.1.3 B
Shoulder height 4.1.4 B
Elbow height 4.1.5 C
Iliac spine height, standing 4.1.6 B
Crotch height 4.1.7 B
Tibial height 4.1.8 B
Chest depth, standing 4.1.9 A, B
Body depth, standing 4.1.10 A, B
Chest breadth, standing 4.1.11 A
Hip breadth, standing 4.1.12 A
Sitting height (erect) 4.2.1 D
Eye height, sitting 4.2.2 D
Cervicale height, sitting 4.2.3 D
Shoulder height, sitting 4.2.4 D
Elbow height, sitting 4.2.5 D
Shoulder-elbow length 4.2.6 C
Elbow-wrist length 4.2.7 C
Shoulder (biacromial) breadth 4.2.8 A, B
Shoulder (bideltoid) breadth 4.2.9 A, B
Elbow-to-elbow breadth 4.2.10 D
Hip breadth, sitting 4.2.11 D
Lower leg length 4.2.12 D
Thigh clearance 4.2.13 D
Knee height 4.2.14 D
Abdominal depth, sitting 4.2.15 D
Thorax depth (nipple) 4.2.16 B
Buttock-abdomen depth, sitting 4.2.17 D
Forearm-fingertip length 4.4.5 C
Buttock-popliteal length 4.4.6 D
Buttock-knee length 4.4.7 D
Neck circumference 4.4.8 A, B
Chest circumference 4.4.9 A
Waist circumference 4.4.10 A
Wrist circumference 4.4.11 A
Thigh circumference 4.4.12 A
Calf circumference 4.4.13 A
NOTE For whole-body scanners, depending on the type of scanning system used, the positions
according to A.3.4 could also be useful for extracting the indicated dimensions.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Table 2 — ISO 7250 measurements by head scanner
Dimension ISO 7250:1996
Head length 4.3.9
Head breadth 4.3.10
Face length 4.3.11
Head circumference 4.3.12
Sagittal arc 4.3.13
Bitragion arc 4.3.14
Table 3 — ISO 7250 measurements by hand or foot scanner
Dimension ISO 7250:1996
Hand length 4.3.1
Palm length perpendicular 4.3.2
Hand breadth (metacarpals) 4.3.3
Index finger length 4.3.4
Index finger breadth, proximal 4.3.5
Index finger breadth, distal 4.3.6
Foot length 4.3.7
Foot breadth 4.3.8
4.2 Standard values
The human body is difficult to measure and does not lend itself to standards of accuracy that might be applied
to machine tooling, for example. For the purposes of this International Standard, the standard for accuracy of
a measurement extracted from a 3-D image is the corresponding traditional measurement, when measured by
[2], [3], [4]
a skilled anthropometrist . The difference between an extracted measurement and the corresponding
traditional measurement on actual subjects should be derived using the test methods given in Clause 5. If the
values are lower than those specified in Table 4, then the measurement may be included in ISO 15535
databases.
As any good scientific report documents the observer and measurer error, the accuracy of extracted
measurements should be reported in any documentation that results from the use of these systems.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Table 4 — Maximum allowable error between extracted value and traditionally measured value
Maximum mean difference
(see 5.3)
Measurement type
mm
Segment lengths (e.g. buttock-popliteal length) 5
Body heights (e.g. shoulder height) 4
Large circumferences (e.g. chest circumference) 9
Small circumferences (e.g. neck circumference) 4
Body breadths (e.g. biacromial breadth) 4
Body depths (e.g. chest depth) 5
Head dimensions without hair 1
Head dimensions with hair 2
Hand dimensions 1
Foot dimensions 2
5 Research designs for establishing accuracy of body dimensions extracted from
scanners
5.1 General
The purpose of this International Standard is to ensure that body measurements obtained from 3-D systems
are sufficiently close to those produced by ISO 7250 traditional methods that they can be substituted for one
another without compromising the validity of ISO standards relying on the data. Annex A contains information
that will be helpful in meeting this goal. In order to demonstrate that a 3-D system is in conformance with this
International Standard, a validation study shall be conducted.
5.2 Validation study procedures
All ISO 7250 variables that are to be measured by 3-D methods shall be included in the validation study.
The 3-D scanning and data extraction system used shall be exactly the same hardware and software
configuration that will be used in collecting the ISO 7250 data.
The traditional measurer shall be an expert, trained and experienced in ISO 7250 techniques. He or she shall
have recently practiced the ISO 7250 protocols for the body measurements in the study. It is preferable that
the same expert measure all test subjects. If landmarks are to be marked prior to scanning, the positioning of
landmarks should be done by an expert trained and experienced in ISO 7250 techniques.
Each subject shall be scanned and measured traditionally at least once. The order of scan and measuring
shall be counterbalanced to control for measurement order effects; however they shall occur sequentially on
the same day in order to minimize error introduced by transient intra-individual fluctuations in body dimensions
(see Annex A).
5.3 Sampling size and test subject selection
A power analysis such as that presented in Clause 6 shall be done in order to ensure that the validation study
sample size is large enough to detect mean scan-measure differences of the magnitudes presented in Table 4
with 95 % confidence. A sample of at least 40 test subjects is recommended, since this will ensure 95 %
confidence in the validation test results for large circumferences such as chest, waist, and hip, which are
particularly difficult to measure for both traditional and 3-D measurement systems.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
Validation test subjects shall reflect approximately the same range of body sizes and shape variations
expected in the study population that will be measured by the 3-D system. If both males and females will be
surveyed, then the validation sample shall include an equal number of each sex. The validation sample shall
also include a variety of body types — not just people of average height and weight. If children are to be
measured, it is particularly important that the validation sample cover the age range of the intended survey.
5.4 Analytical procedures
After data collection is complete, the difference (d) between the scan value and the measured value (d = scan
minus measure) shall be computed for each variable and test subject, and the mean of these differences shall
be calculated for each variable and reported with its associated standard deviation, sample size and 95 %
confidence Interval. If the 95 % confidence interval for the mean of scan-minus-measure differences is within
the plus or minus interval defined by the values in Table 4, then the 3-D system can be said to give results
sufficiently comparable to ISO 7250 methods such that the 3-D data may be used in standards relying on
ISO 7250 protocols.
5.5 Validation study reporting
A report of the validation study shall be published and/or included in the anthropometric survey report
associated with any 3-D database provided for use in standards relying on ISO 7250 protocols. This report
shall include the following information:
⎯ demography (age, sex) and anthropometry (height, weight) of the test subjects;
⎯ protocols for measuring and scanning, including subject clothing, anthropometric landmarks, and body
positions;
⎯ name and pertinent details (or references) describing the 3-D system being validated, including hardware
model number, and software version number;
⎯ means, standard deviations, sample sizes for each body dimension as measured by scanning and as
measured traditionally;
⎯ means, standard deviations, sample sizes, and 95 % confidence intervals for scan-minus-measure
differences for each body dimension
6 Method for estimating the number of subjects needed
6.1 In order for scanner-measurer comparisons to be statistically valid, it is important that test samples be
large enough to detect mean differences of the magnitude specified in Table 4 at least 95 % of the time, at the
level of 0,05 or better.
6.2 Assuming that the differences observed between extracted values and measured values are normally
distributed, the minimum sample size required for a one-sample test of differences can be estimated using the
[5]
following power equation :
2
s
2
n=× 1, 96+ 1, 65
()
2
δ
where
s is the standard deviation of extracted minus measured differences;
δ is the magnitude of extracted minus measured difference that must be detected;
1,96 is the critical Z value for a two-sided 0,05 level test;
1,65 is the critical Z value for 95 % confidence.
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SIST EN ISO 20685:2006
ISO 20685:2005(E)
6.3 In practice, the true standard deviation of extracted minus measured differences for a particular system
is usually unknown, so it is estimated from previous studies of similar systems. A pilot study could be
necessary. The magnitude of difference to be detected (δ ) is obtained from Table 4 and varies among
different classes of body dimensions.
6.4 Because the variance of extracted minus measured differences is different for each body dimension,
and because the magnitude of extracted minus measured differences to be detected also varies among
dimension classes, the investigator usually makes several sample-size estimates for different body
dimensions, and chooses the largest result to establish the minimum sample size required. When this
approach is taken, the calculated sample size will be sufficient for 95 % confidence in 0,05 level tests in the
worst case, and it will be more than sufficient for all the other body dimensions.
EXAMPLE Suppose an investigator wishes to establish the validity of using scan-extracted circumferences in place
of directly measured circumferences. Previous studies resulted in extracted-minus-measured differences with standard
deviations
...
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