ASTM D4697-95
(Guide)Standard Guide for Maintaining Test Methods in the User's Laboratory
Standard Guide for Maintaining Test Methods in the User's Laboratory
SCOPE
1.1 This guide is intended to assist laboratories in maintaining precision and controlling bias in testing. It includes statistical procedures for detecting lack of control, changes in calibration constants, and in operator technique. Suggestions are given for the correction of some out of control situations.
1.2 This guide includes the following topics: Topic Title SectionNumberScope1Referenced Documents2Terminology3Significance and Use4Calibration Control5Test Performance Control6
Annexes:
Calibration ControlAnnex A1Test Performance ControlAnnex A2
1.3 This standard does not give all of the details for preparing statistical quality control charts or the statistical tests used to interpret them, but such information may be found easily in a number of publications.
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Designation: D 4697 – 95
Standard Guide for
Maintaining Test Methods in the User’s Laboratory
This standard is issued under the fixed designation D 4697; the number immediately following the designation indicates the year of
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 (e) indicates an editorial change since the last revision or reapproval.
19428, USA. The control chart parameters described in the annexes of this
1. Scope
guide can be calculated with one of these programs and the control charts
1.1 This guide is intended to assist laboratories in maintain-
screen plotted.
ing precision and controlling bias in testing. It includes
statistical procedures for detecting lack of control, changes in 3. Terminology
calibration constants, and in operator technique. Suggestions
3.1 Definitions:
are given for the correction of some out of control situations.
3.1.1 accuracy, n—of a test method, the degree of agree-
1.2 This guide includes the following topics:
ment between the true value of the property being tested (or an
Section
accepted standard value) and the average of many observations
Topic Title Number
made according to the test method, preferably by many
Scope 1
Referenced Documents 2 observers. (See also bias and precision.)
Terminology 3
3.1.2 attribute data, n—observed values or determinations
Significance and Use 4
which indicate the presence or absence of specific character-
Calibration Control 5
Test Performance Control 6 istics.
3.1.3 bias, n—in statistics, a constant or systematic error in
Annexes:
test results.
Calibration Control Annex A1 3.1.3.1 Discussion—Bias can exist between the true value
Test Performance Control Annex A2
and a test result obtained from one method; between test results
from two methods; or between two test results obtained from a
1.3 This standard does not give all of the details for
single method, for example, between operators or between
preparing statistical quality control charts or the statistical tests
laboratories.
used to interpret them, but such information may be found
3.1.4 calibrate, vt—to determine and record the relationship
easily in a number of publications.
between a set of standard units of measure and the output of an
2. Referenced Documents
instrument or test procedure.
2.1 ASTM Standards: 3.1.5 calibration, n—the act or process of calibrating; the
recorded relationship resulting from calibrating.
D 123 Terminology Relating to Textiles
3.1.6 measurement value, n—the numerical result of quan-
D 1578 Test Method for Breaking Strength of Yarn in Skein
tifying a particular property or dimension. (Syn. measurement,
Form
measurement datum.)
E 456 Terminology Relating to Quality and Statistics
3.1.7 moving range, MR, n—the difference without regard
2.2 ASTM Adjuncts:
to sign between two successive observations.
TEX-PAC
3.1.8 precision, n—the degree of agreement within a set of
NOTE 1—Tex-Pac is a group of PC programs on floppy disks, available
observations or test results obtained as directed in a test
through ASTM Headquarters, 100 Barr Harbor Drive, Conshohocken, PA
method.
3.1.8.1 Discussion—The term “precision” delimited in vari-
This guide is under the jurisdiction of ASTM Committee D-13 on Textiles and
ous ways is used to describe different aspects of precision. This
is the direct responsibility of Subcommittee D13.93 on Statistics.
usage was chosen in preference to the use of “repeatability”
Current edition approved May 15, 1995. Published July 1995. Originally
and “reproducibility” which have been assigned conflicting
published as D 4697 – 87. Last previous edition D 4697 – 91.
For information see: Juran, J. M., ed., Quality Control Handbook, McGraw meanings by various authors and standardizing bodies.
Hill, New York, 4th ed., 1988; Manual on Presentation of Data and Control Chart
3.1.9 test method, n—a definitive procedure for the identi-
Analysis, ASTM STP 15D, ASTM, 1976; and Statistical Quality Control Handbook,
fication, measurement, and evaluation of one or more qualities,
Western Electric Co., Inc., 2nd ed., 1985 (Inquiries may be made to: AT& T
characteristics, or properties of a material, product, system, or
Technologies, Commercial Sales Clerk, Select Code 700-444, P.O. Box 19901,
Indianapolis, IN 44219).
service that produces a test result.
Annual Book of ASTM Standards, Vol 07.01.
3.1.10 verification, n—the act or process of verifying.
Annual Book of ASTM Standards, Vol 14.02.
5 3.1.11 verify, vt—(1) to determine whether a previously
PC programs on floppy disks are available through ASTM. For a 3 ⁄2 inch disk
calibrated instrument, standard solution, or other standard is
request PCN:12-429040-18, for a 5 ⁄4 inch disk request PCN:12-429041-18.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
D 4697
still properly calibrated; (2) to establish that an operation has 5.3.2 In the case of calibration control, it is seldom neces-
been completed correctly. sary to plot a control chart for the range of specimens. This
3.1.12 For definitions of textile terms in this standard, refer aspect of test method maintenance will usually be well
to Terminology D 123. For definitions of statistical terms in controlled when the directions in 6.1, 6.2, and 6.5 are followed.
this standard, refer to Terminology D 123 or Terminology
6. Test Performance Control
E 456.
6.1 Standard Sample—Reserve an adequate supply of a
3.2 Definitions of Terms Specific to This Standard:
stable standard sample of material for maintaining test perfor-
3.2.1 maintain—to monitor the usage of test methods and to
mance (Note 2). Each day, before making a test on unknown
take remedial steps when necessary.
laboratory samples, have each analyst run an analysis on the
standard sample. Have the analyst use the machine he will use
4. Significance and Use
later to test the unknown samples.
4.1 Following this guide will aid the user in maintaining
control of both the bias and the precision of any test method.
NOTE 2—It is essential to obtain a new supply of a standard material
4.1.1 It is necessary to control bias so that, if a change in well before the old supply is exhausted, and to run the old supply and the
new supply in parallel for a short length of time.
level of an unknown material under test occurs, the user can be
confident that the change was not due to the execution of the 6.1.1 If a supply of a stable standard sample cannot be
obtained, there are techniques available for overcoming this
test method.
4.1.2 It is also necessary to control precision so that the problem. For example, two analysts could analyze a specimen
from the same sample at the same time, and the difference
established confidence limits and critical differences will be
maintained. between the two results could be plotted. For problems of this
4.2 Should the use of the test method be out of control, this kind, competent statistical help is required in the planning of
the program, the presentation, and analysis of the data.
guide will detect it, and may give an indication of where the
problem lies. 6.2 Quality Control Chart—Using the standard sample test
data, establish statistical quality control charts for the test
5. Calibration Control
results produced by each analyst-instrument pair. If there is
5.1 Calibration Procedure—To be completely useful, the more than one analyst-instrument pair, plot a separate average
test method must contain a calibration procedure if it makes and range chart for each pair, using the same control lines (for
use of a reagent, apparatus, or standard that is subject to change an example, see Annex A2).
with age or use. If it does not have a calibration procedure, then 6.3 Average Center Line—Use the established expected test
one should be obtained or written and incorporated in the value of the standard sample as the center line on the chart for
method. averages. This value may have been obtained with a standard
5.2 Calibration Records—Establish for ea
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