ASTM E177 : 90a(2002)

Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods

Standard Details

1.1 The purpose of this practice is to present concepts necessary to the understanding of the terms "precision" and "bias" as used in quantitative test methods. This practice also describes methods of expressing precision and bias and, in a final section, gives examples of how statements on precision and bias may be written for ASTM test methods. The term "accuracy", used in earlier editions of Practice E 177, embraces both precision and bias (see Section 20 and Note 4).

1.2 Informal descriptions of the concepts are introduced in the text as the concepts are developed, and appear in the following sections:

	Section
Terminology	3
Significance and Use	4

GENERAL CONCEPTS

Test Method	5
Measurement Terminology	6
Observation	7
Test Determination	8
Test Result	9

SOURCES OF VARIABILITY

Experimental Realization of a Test Method	10
Operator	11
Apparatus	12
Environment	13
Sample	14
Time	15

STATISTICAL CONCEPTS

Accepted Reference Value	16
Statistical Control	17
Precision	18
Bias	19
Accuracy	20
Variation of Precision and Bias with Material	21
Variation of Precision and Bias with Sources of Variability	22

COMBINATIONS OF SOURCES OF VARIABILITY

Repeatability and Laboratory Bias	23
Other Within-a-Single Laboratory Precisions	24
Reproducibility and Bias of the Test Method	25
Range of Materials	26

METHODS OF EXPRESSING PRECISION AND BIAS

Indexes of Precision	27
Preferred Indexes of Precision for ASTM Test Methods	28
Preferred Statements of Bias for ASTM Test Methods	29
Elements of a Statement of Precision and Bias	30

STATEMENTS OF PRECISION AND BIAS

Examples of Statements of Precision and Bias	31

APPENDIX

Alphabetical List of Descriptions of Terms from the Text	X1

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.