ISO 15572:1998
(Main)Guide for estimating uncertainties in dosimetry for radiation processing
Guide for estimating uncertainties in dosimetry for radiation processing
Guide pour l'estimation des incertitudes en dosimétrie pour le traitement par irradiation
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Standards Content (Sample)
INTERNATIONAL IS0
STANDARD 15572
First edition
1998-12-15
Guide for estimating uncertainties in
dosimetry for radiation processing
Guide pour /‘estimation des incertitudes en dosimktrie pour le traitement par
irradiation
Reference number
IS0 15572: 1998(E)
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IS0 15572: 1998(E)
Foreword
IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies
(IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 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. IS0 collaborates closely with the International Electrotechnical
Commission (IEC) on all matters of electrotechnical standardization.
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.
lnternationai Standard IS0 15572 was prepared by the American Society for Testing and Materials (ASTM)
Subcommittee E1O.O1 (as E 1707-95) and was adopted, under a special “fast-track procedure ”, by Technical
Committee ISOKC 85, Nuclear energy, in parallel with its approval by the IS0 member bodies.
A new ISOrK 85 Working Group WG 3, High-level dosimetry for radiation processing, was formed to review the
voting comments from the IS0 “Fast-track procedure” and to maintain these standards. The USA holds the
convenership of this working group.
International Standard IS0 15572 is one of 20 standards developed and published by ASTM. The 20 fast-tracked
standards and their associated ASTM designations are listed below:
IS0 Designation ASTM Designation Title
15554 E 1204-93 Practice for dosimetry in gamma irradiation facilities for food
processing
15555 E 1205-93 Practice for use of a ceric-cerous sulfate dosimetry system
E1261-94 Guide for selection and calibration of dosimetry systems for
15556
radiation processing
15557 E 1275-93 Practice for use of a radiochromic film dosimetry system
15558 E 1276-96 Practice for use of a polymethylmethacrylate dosimetry system
15559 E 1310-94 Practice for use of a radiochromic optical waveguide dosimetry
system
15560 E 1400-95a Practice for characterization and performance of a high-dose
radiation dosimetry calibration labora tory
15561 E 1401-96 Practice for use of a dichromate dosimetry system
0 IS0 1998
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 l CH-1211 Geneve 20 l Switzerland
Internet iso@ iso.ch
Printed in Switzerland
ii
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@ IS0 IS0 15572:1998(E)
E1431-91 Practice for dosimetry in electron and bremsstrahlung irradiation
15562
facilities for food processing
15563 E 1538-93 Practice for use of the ethanol-chlorobenzene dosimetry system
15564 E 1539-93 Guide for use of radiation-sensitive indicators
15565 E 1540-93 Practice for use of a radiochromic liquid dosimetry system
E 1607-94 Practice for use of the alanine-EPR dosimetry system
15566
15567 E 1608-94 Practice for dosimetry in an X-ray (bremsstrahlung) facility for
radiation processing
of calorimetric dosimetry systems electron
15568 E 1631-96 Practice for use
beam dose meas Nurements and dosimeter calibrations
Practice for dosimetry in an electron-beam facility for radiation
E 1649-94
15569
processing at energies between 300 keV and 25 MeV
E 1650-94 Practice for use of cellulose acetate dosimetry system
15570
Practice for dosimetry in a gamma irradiation facility for radiation
15571 E 1702-95
processing
Guide for estimating uncertainties in dosimetry for radiation
15572 E 1707-95
processing
Practice for dosimetry in an electron-beam facility for radiation
15573 E 1818-96
processing at energies between 80 keV and 300 keV
. . .
III
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IS0 15572: 1998(E)
@ IS0
AMERICAN SOCIEN FOR TESTING AND MATERIALS
1916 Race St. Philadelphia, Pa 19103
Designation: E 1707 - 95
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
If not listed in the current combined index, will appear in the next edition.
Standard Guide for
Estimating Uncertainties in Dosimetry for Radiation
Processing’
number immediately following the designation indicates the year of
This standard is issued under the fixed designation E i 707; till-
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (c) indicates an editorial change since the last revision or reapproval.
E 1026 Practice for Using the Fricke Reference Standard
1. Scope
Dosimetry System3
1.1 This guide defines possible sources of error in
E 1204 Practice for Dosimetry in Gamma Irradiation
dosimetry performed in gamma, x-ray (bremsstrahlung) and
Facilities for Food Processing3
electron irradiation facilities and offers procedures for esti-
E 1205 Practice for Use of a Ceric-Cerous Sulfate
mating the resulting magnitude of the uncertainties in the
Dosimetry System3
measurement results. Basic concepts of measurement, esti-
E 1249 Practice for Minimizing Dosimetry Errors in
mate of the measured vaiue of a quantity, “true” value, error
Radiation Hardness Testing of Silicon Electronic De-
and uncertainty are defined and discussed. Components of
vices Using Co-60 Sources3
uncertainty are discussed and methods are given for evalu-
E 126 1 Guide for Selection and Calibration of Dosimetry
ating and estimating their values. How these contribute to
I Systems for Radiation Processing3
the standard uncertainty in the reported values of absorbed
1275 Practice for Use of a Radiochromic Film
E
dose are considered and methods are given for calculating
Dosimetry System3
the combined standard uncertainty and an estimate of
E 1276 Practice for Use of a Polymethylmethacrylate
overall (expanded) uncertainty. The methodology for evalu-
Dosimetry System3
ating components of uncertainty follows IS0 procedures (see
E 13 10 Practice for the Use of a Radiochromic Optical
2.3). The traditional concepts of precision and bias are not
Waveguide Dosimetry System3
used. Examples are given in five appendixes.
E 1401 Practice for Use of a Dichromate Dosimetry
1.2 This guide assumes a working knowledge of statistics.
System3
Several statistical texts are included in the references (1, 2, 3,
,
E 143 1 Practice for Dosimetry in Electron and
2
4)
Bremsstrahlung Irradiation Facilities for Food
‘1.3 This standard does not purport to address all of the
Processing3
sq&y concerns, if any, associated with its use. It is the
E 1607 Practice for Use of the Alanine-EPR Dosimetry
responsibility of the user o/this standard to establish appro-
System3
pritie safety and health practices and determine the applica-
2.2 ICRU Reports!
bility of regulatory limitations prior to use.
ICRU Report 14 Radiation Dosimetry: X-Rays and
Gamma Rays with Maximum Photon Energies Between
0.6 and 50 MeV
2. Referenced Documents
ICRU Report 17 Radiation Dosimetry: X-Rays Generated
at Potentials of 5 to 150 kV
2.1 ASTM Standards:
ICRU Report 33 Radiation Quantities and Units
E 170 Terminology Relating to Radiation Measurements
ICRU Report 34 The Dosimetry of Pulsed Radiation
and Dosimetry3
ICRU Report 35 Radiation Dosimetry: Electron Beams
E 177 Practice for Use of the Terms Precision and
with Energies Between 1 and 50 MeV
Accuracy as Applied to Measurement of a Property of a
ICRU Report 37 Stopping Powers for Electrons and
Material3
Positrons
E 178 Practice for Dealing With Outlying Observations3
b
23
.
E 456 Terminology Relating to Quality and Statistics4
E 666 Practice for Calculating Absorbed Dose from
3. Terminology
Gamma or X Radiation3
3.1 Definitions:
E 876 Practice for Use of Statistics In the Evaluation of
3.1.1 absorbed dose, D-quantity of radiation energy
Spectrometric Data5
imparted per unit mass of a specified material. The unit of
absorbed dose is the gray (Gy) where 1 gray is equivalent to
the absorption of 1 joule per kilogram (= 100 rad). The
i This guide is under the jurisdiction of ASTM Committee E-10 on Nuclear
mathematical relationship is the quotient of&by dm, where
Technology and Applications and is the direct responsibility of Subcommittee
E 10.0 I on Dosimetry for Radiation Processing. & is the mean energy imparted by ionizing radiation to
Current edition approved May 15, 1995. Published July 1995.
matter of mass dm (see ICRU 33).
2 The boldface numbers in parentheses refer to a list of references at the end of
this guide.
3 Annual Book of ASTM Slandards, Vol 12.02.
6 Available from International Commission on Radiation Units and Measure-
4 Annual Book ofASTM Standards, Vol 14.02.
ments, 79 IO Woodmont Ave., Suite 800 Bethesda, MD 208 14.
5 Annual Book of ASTM Standards, Vol 03.06.
1
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IS0 15572:1998(E) 0 IS0
D = &/dm 3.1.15 expected value- sum of possible values of a vari-
able weighted by the probability of the value occurring. It is
3.1.2 accuracy of measurement-closeness of the agree-
found from the expression:
ment between the result of a m ‘easurement and the true value
E(v) = Zi PiVi
of the measurand.
3.1.3 calibration curve-graphical representation of the
where:
relationship between dosimeter response and absorbed dose
Y. = zth value and
for a given dosimetry system. For a mathematical represen-
Pi’ = probabilky of zth value.
tation, see response function.
3.1.16 influence quantity-quantity that is not included in
3.1.4 coeficient of variation-sample standard deviation
the specification of the measurand but that nonetheless
expressed as a percentage of sample mean value (see 3.37 and
affects the result of the measurement.
3.38).
DIscussroN-This quantity is understood to include values associated
(Cv) = s,-,/x x 100 %
with measurement reference standards, reference materials, and refer-
3.1.5 combined standard uncertainty-standard uncer- ence data upon which the result of the measurement may depend, as
well as phenomena such as short-term instrument fluctuations and
tainty of the result of a measurement when that result is
parameters such as temperature, time, and humidity.
obtained from the values of a number of other quantities,
equal to the positive square root of a sum of terms, the terms 3.1.17 (measurable) quantity-attribute of a phenom-
enon, body or substance that may be distinguished qualita-
being the variances or covariances of these other quantities
weighted according to how the measurement result varies tively and determined quantitatively; for example, the spe-
with changes in these quantities. cific quantity of interest in this guide is absorbed dose.
3.1.6 confidence interval-an interval estimate that con- 3.1.18 measurand-specific quantity subject to measure-
tains the mean value of a parameter with a given probability. ment.
3.1.7 confidence level--the probability that a confidence
DISCU~SON-A specification of a measurand may include statements
interval estimate contains the value of a parameter.
about other quantities such as time, humidity, or temperature. For
3.1.8 corrected result-result of a measurement after cor- example, equilibrium absorbed dose in water at 25°C.
rection for the best estimate of systematic error.
3.1.19 measurement-set of operations having the object
3.1.9 correction- value that, added algebraically to the
of determining a value of a quantity.
uncorrected result of a measurement, compensates for sys-
3.1.20 measurement procedure-set of operations, in spe-
tematic error.
cific terms, used in the performance of particular measure-
DIscussroN-The correction is equal to the negative of the systematic ments according to a given method.
error. Some systematic errors may be estimated and compensated by
3.12 1 measurement system-system used for evaluating
applying appropriate corrections. However, since the systematic error
the measurand.
cannot be known perfectly, the compensation cannot be complete.
3.1.22 measurement traceability-The ability to demon-
3.1.10 correction jktor- numerical factor by which the
strate and document on a continuing basis that the measure-
uncorrected result of a measurement is multiplied to com-
ment results from a particular measurement system are in
pensate for a systematic error.
agreement with comparable measurement results obtained
with a national standard (or some identifiable and accepted
DIscussroN-Since the systematic error cannot be known perfectly,
the compensation cannot be complete. standard) to a specified uncertainty.
3.1.23 method ofmeasurement-logical sequence of oper-
3.1.11 coverage factor- numerical factor used as a multi-
ations used in the performance of measurements according
plier of the combined standard uncertainty in order to obtain
to a given principle.
an overall uncertainty.
DIscu~roN-Methods of measurement may be qualified in various
DISCUSSION-A coverage factor, k, is typically in the range of 2 to 3
ways such as: substitution method, differential method, and null
(see 8.3).
method.
3.1.12 dosimeter batch-quantity of dosimeters made
3.1.24 outlier-a measurement result that deviates mark-
from a specific mass of material with uniform composition,
edly from others within a set of measurement results.
fabricated in a single production run under controlled,
3.1.25 overall uncertainty-quantity defining the interval
consistent conditions and having a unique identification
about the result of a measurement within which the values
code.
that could reasonably be attributed to the measurand may be
3.1.13 dosimetry system- a system used for determining
expected to lie with a high level of confidence.
absorbed dose, consisting of dosimeters, measurement in-
]DISCusSION-Overall uncertainty is referred to as “expanded uncer-
struments and their associated reference standards, and
tainty” (see Guide to the Expression of Uncertainty in Measurement)
procedures for the system ’s use,
(5).’ To associate a specific level of confidence with the interval defined
3.1.14 error (of measurement)-result of a measurement
by the overall uncertainty requires explicit or implicit assumptions
minus a true value of the measurand.
regarding the probability distribution characterized by the measurement
result and its combined standard uncertainty. The level of confidence
DrscusWN+-Since a true value cannot be determined, in practice a
that may be attributed to this interval can be known only to the extent to
conventional true value is used. The quantity is sometimes called
which such assumptions may be justified.
“absolute error of measurement” when it is necessary to distinguish it
from relative error. If the result of a measurement depends on the values
of quantities other than the measurand, the errors of the measured
values of these quantities contribute to the error of the result of the
7 Available from International Organization for Standardization, Case Postal
measurement. 56, CH- 12 1 1 Geneva 20 Switzerland.
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IS0 15572: 1998(E)
d# El707
-mathematical representation of
3.1.26 primary standard dosimeter-a dosimeter of the 3.1.35 response function
the relationship between dosimeter response and absorbed
highest metrological quality, established and maintained as
dose for a given dosimetry system. -
an absorbed dose standard by a national or international
standards organization. 3.1.36 result of a measurement-value attributed to a
3.1.27 principle of measurement-scientific basis of a measurand, obtained by measurement.
method of measurement.
DrscussroN-when the term “result of a measurement” is used, it
-a method of estimating overall uncer-
3.1.28 quadrature
should be made clear whether it refers to: the indication, the uncorrected
tainty from independent sources by taking the square root of
result, the corrected result, and whether severa! VZIWS are averaged. A
the sum of the squares of individual components of uncer-
complete statement of the result of the measurement includes informa-
tion about the uncertainty of the measurement.
tainty (for example, coefficient of variation).
3.1.29 random error-result of a measurement minus the
3.1.37 routine dosimeter-dosimeter calibrated against a
mean result of a large number of measurements of the same
primary-, reference-, or transfer-standard dosimeter and used
measurand that are made under repeatable or reproducible
for routine dosimetry measurement.
conditions (see 3.32 and 3.33).
3.1.38 sample mean -a measure of the average value of a
data set which is representative of the population. It is
DIscussroN-In these definitions (and that for systematic error), the
term “mean result of a large number of measurements of the same determined by summing all the values in the data set and
measurand” is understood to mean “the expected value or mean of all
dividing by the number of items (n) in the data set. It is
possible measured values of the measurand obtained under conditions of
found from the expression:
repeatability or reproducibility ”. This ensures that the definition cannot
be misinterpreted to imply that for a series of observations, the random
1
js=-
= 1,2,3.n
n 2 Xi9 i
error of an individual observation is known and can be eliminated by
applying a correction. The view of this guide is that error is an idealized
i
concept and that errors cannot be known exactly.
3.1.39 sample standard deviation, S,-,-measure of dis-
persion of values expressed as the positive square root of the
3.1.30 reference standard dosimeter-a dosimeter of high
sample variance.
metrological quality, used as a standard to provide measure-
3.1.40 sample variance-the sum of the squared devia-
ments traceable to and consistent with measurements made
tions from the sample mean divided by (n-l), given by the
using primary standard dosimeters.
expression:
3.1.3 1 reference value (ofa quantity)-value attributed to
a specific quantity and accepted, sometimes by convention,
- X)2
p-, = = cxi
as having an uncertainty appropriate for a given purpose; for
(n- 1)
example, the value assigned to the quantity realized by a
where:
reference standard.
= individual value of parameter with i = 1, 2. . .n, and
xi
DIscussroN-This is sometimes called “assigned value ”, or “assigned
x = mean of n values of parameter (see 3.37).
reference value ”.
3.1.4 1 standard uncertainty-uncertainty of the results of
a measurement expressed as a standard deviation.
3.1.32 relative error (of measurement)-error of measure-
3.1.42 systematic error -mean result of a large number of
ment divided by a true value of the measurand.
repeated measurements of the same measurand minus a true
DrSCuSSIOr+-Since a true value cannot be determined, in practice a
value of the measurand.
reference value is used.
DIscussroN-The repeated measurements are carried out under the
3.1.33 repeatability (of results of measurements)-close- conditions of the term “repeatability ”. Like true value, systematic error
and its causes cannot be completely known. The error of the result of a
ness of the agreement between the results of successive
measurement may often be considered as arising from a number of
measurements of the same measurand carried out subject to
random and systematic effects that contribute individual components of
all of the following conditions: the same measurement
error to the error of the result (see E 170, E 177, and E 456).
procedure, the same observer, the same measuring instru-
ment, used under the same conditions, the same location, 3.1.43 traceability-see measurement traceability.
and repetition over a short period of time. 3.1.44 transfer standard dosimeter-a dosimeter, often a
reference standard dosimeter, suitable for transport between
DIscussroN-These conditions are called “repeatability conditions.”
different locations for use as an intermediary to compare
Repeatability may be expressed quantitatively in terms of the dispersion
absorbed dose measurements.
characteristics of the results.
3.1.45 true value-value of measurand that would be
3.1.34 reproducibility (of results of measurements)-close-
obtained by a perfect measurement.
ness of agreement between the results of measurements of
DIscussroN-True values are by nature indeterminate and only an
the same measurand, where the measurements are carried
idealized concept. In this guide the terms “true value of a measurand”
out under changed conditions such as differing: principle or
and “value of a measurand” are viewed as equivalent (see 5.1.1).
method of measurement, observer, measuring instrument,
3.1.46 Type A evaluation (of standard uncertainty)-
location, conditions of use, and time.
method of evaluation of a standard uncertainty by the
DISCUSSION-A valid statement of reproducibility requires specifica-
statistical analysis of a series of observations.
tion of the conditions changed. Reproducibility may be expressed
3.1.47 Type B evaluation (of standard uncertainty)-
quantitatively in terms of the dispersion characteristics of the results. In
method of evaluation of a standard uncertainty by means
this context, results of measurement are understood to be corrected
results. other than the statistical analysis of a series of observations.
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IS0 15572: 1998(E)
3.1.48 uncertainty (of measurement)-a parameter, asso- for the result of a measurement therefore ultimately depends
on the understanding, critical analysis, and integrity of those
ciated with a measurand or derived quantity, that character-
who contribute to the assignment of its val ’ue.
izes the distribution of the values that could reasonably be
attributed to the measurand or derived quantity.
DIScuss!oN-For example, uncertainty may be a standard deviation 5. Basic Concepts- Components of Uncertainty
(or a given multiple of it), or the width of a confidence interval.
5. I Measurement.
Uncertainty of measurement comprises, in general, many components.
5.1.1 The objective of a measurement is to determine the
Some of these components may be evaluated from the statistical
value of the measurand, that is, the value of the specific
distribution of the results of series of measurements and can be
characterized by experimental standard deviations. The other compo- quantity to be measured. A measurement therefore begins
nents, which can also be characterized by standard deviations, are
with an appropriate specification of the measurand, the
evaluated from assumed probability distributions based on experience or
method of measurement, and the measurement procedure.
other information. It is understood that all components of uncertainty
5.1.2 In general, the result of a measurement is only an
contribute to the distribution.
approximation or estimate of the value of the measurand
3.1.49 uncorrected result-result of a measurement before
and thus is complete only when accompanied by a statement
correction for the assumed systematic error.
of the uncertainty of that estimate.
3.1.50 value (of a quantity)-magnitude of a specific
5.1.3 In practice, the specification or definition of the
quantity generally expressed as a number with a unit of
measurand depends on the required accuracy of the mea-
measurement, for example, 25 kGy.
surement. The measurand should be defined with sufficient
exactness relative to the required accuracy so that for all
4. Significance and Use
practical purposes the measurand value is unique.
4.1 Gamma, electron and x-ray (bremsstrahlung) facilities
NOTE 2-Incomplete definition of the measurand can give rise to a
routinely irradiate a variety of products such as food,
component of uncertainty sufficiently large that it must be included in
medical devices, aseptic packaging and commodities (see
the evaluation of the uncertainty of the measurement result.
Practices E 1204 and E 143 1). Process parameters for the
products must be carefully controlled to ensure that these 5.1.3.1 Although a measurand should be defined in sufTi-
cient detail that any uncertainty arising from its incomplete
products are processed within specifications (see ANSI/
definition is negligible in comparison with the required
AAMI ST3 l-1 990, ANSI/AAMI ST32- 199 1 and IS0 11137
accuracy of the measurement, it must be recognized that this
(6, 7, 8)? Accurate dosimetry is essential in process control
may not always be practicable. The definition may, for
(see Guide E 126 1). For absorbed dose measurements to be
meaningful, the overall uncertainty associated with these example, be incomplete because it does not specify parame-
measurements must be estimated and its magnitude quanti- ters that may have been assumed, unjustifiably, to have
negligible effect; or it may imply conditions that can never
fied .
fully be met and whose imperfect realization is difficult to
NOTE I-For a comprehensive discussion of various dosimetry
take into account.
methods applicable to the radiation types and energies discussed in this
5.1.4 In many cases, the result of a measurement is
guide, see ICRU Reports 14, 17, 34, 35 and Reference (9).
determined on the basis of repeated observations. Variations
4.2 This standard guide uses the methodology adopted by
in repeated observations are assumed to arise from not being
the International Organization for Standardization for esti-
able to hold completely constant each influence quantity that
mating uncertainties in dosimetry for radiation processing
can affect the measurement result.
(see 2.3). The ASTM traditionally expresses uncertainty in
5.1.5 The mathematical model of the measurement pro-
terms of precision and bias where precision is a measure of
cedure that transforms the set of repeated observations into
the extent to which replicate measurements made under
the measurement result is of critical importance since, in
specified conditions are in agreement and bias is a systematic
addition to the observations, it generally includes various
error (see Practice E 170, E 177 and E 456). As seen from
influence quantities that are inexactly known. This lack of
this standard, sources of uncertainty are evaluated as either
knowledge contributes to the uncertainty of the measure-
Type A or Type B rather than in terms of precision and bias.
ment result along with the variations of the repeated obser-
Both random and systematic error clearly are differentiated
vations and any uncertainty associated with the mathemat-
from components of uncertainty. The methodology for
ical model itself.
treatment of uncertainties is in conformance with current
5.2 Errors, Efects, and Corrections:
internationally accepted practice. (See Guide to the Expres-
5.2.1 In general, a measurement procedure has imperfec-
sion of Uncertainty in Measurement (5).)
tions that give rise to an error in the measurement result.
4.3 Although this guide provides a framework for as-
Traditionally, an error is viewed as having two components,
sessing uncertainty, it cannot substitute for critical thinking,
namely, a random component and a systematic component.
intellectual honesty, and professional skill. The evaluation of
5.2.2 Random error presumably arises from unpredict-
uncertainty is neither a routine task nor a purely mathemat-
able or stochastic temporal and spatial variations of influ-
ical one; it depends on detailed knowledge of the nature of
ence quantities. The effects of such variations, hereafter
the measurand and of the measurement method and proce-
referred to as random effects, give rise to variations in
dure used, The quality and utility of the uncertainty quoted
repeated observations of the measurand. The random error
of a measurement result cannot be compensated by correc-
tion but it can usually be reduced by increasing the number
8 Available from Association for the Advancement of Medical Instrumentation,
3330 Washington Boulevard, Suite 400, Arlington, VA 22201-4598. of observations; its expectation or expected value is zero.
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0 IS0
IS0 15572: 1998(E)
NOTE 3-The experimental standard deviation of the arithmetic
532.10 variations in repeated observations of the
mean or average of a series of observations is not the random error of the
measurand under apparently identical conditions.
mean, although it is so referred to in some publications on uncertainty.
It is instead a measure of the uncertainty of the mean due to random
NOTE 7-These sources are not necessarily independent and some
effects. The exact value of the error in the mean arising from these
may contribute to 5.3.2.10. Of course, an unrecognized systematic effect
effects cannot be known. In this guide great care is taken to distinguish
cannot be taken into account in the evaluation of the uncertainty of the
between the terms “error” and “uncertainty ”; they are not synonyms
result of a measurement but contributes to its error.
but represent completely different concepts; they should not be confused
with one
...
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