accuracy (of measurement)

Closeness of the agreement between the result of a measurement and a true value of the measurand.
NOTES
1. Accuracy is a qualitative concept. Its quantitative counterpart is error of measurement.
2. IFCC has used this term with the present meaning of trueness.

basic state

Specific state of a system for use as a base for the evaluation of actual states of the system.
NOTE
In clinical laboratory sciences the basic state is represented by the zero value of the state variable.

calibration

Set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system, or values represented by a material measure or a reference material and the corresponding values realized by standards.

characteristic

Property that helps to distinguish between items of a given population

combined standard uncertainty (of a measurement)

Standard uncertainty of the result of a measurement when that result is obtained from the values of a number of other quantities, equal to the positive square root sum of terms, the terms being variances or covariances of these other particular quantities weighted according to how the measurement result varies with changes in these quantities.

conventional true value (of a quantity)

Value attributed to a particular quantity and accepted, sometimes by convention, as having an uncertainty appropriate for a given purpose.
NOTE
Conventional true value is sometimes called 'assigned value' or 'target value' .

drift

Slow change of a metrological characteristic of a measuring instrument.

error (of measurement)

Result of a measurement minus a true value of the measurand.
NOTES
1. When it is necessary to distinguish "error" from "relative error", the former is sometimes called 'absolute error of measurement'.
2. In many instances the error of measurement is called 'total error'.

expanded uncertainty (of a measurement)

Quantity defining an interval about the result of a measurement that may be expected to encompass a large fraction of the distribution of values that could reasonably be attributed to the measurand.

influence quantity

Quantity that is not the measurand but that affects the result of the measurement.
NOTE
In clinical laboratory sciences the component of an influence quantity is usually called 'analytical interferent'.
EXAMPLE
Bilirubin concentration in the measurement of the concentration of creatininium in plasma.

material measure

Device intended to reproduce or supply, in a permanent manner during its use, one or more known values of a given quantity.

measurand

Particular quantity subject to measurement.

measurement procedure

Set of operations, described specifically, used in the performance of particular measurements according to a given method.
NOTES
1. In a quality system a measurement procedure is recorded as a working instructions document, and should be described in sufficient detail to enable an operator to carry out a measurement without additional information.
2. Metrological characteristics such a repeatability, systematic error or minimum detectable value can be assessed in measurement procedures, not in methods of measurement.
EXAMPLE
IFCC reference procedure for the measurement of the catalytic concentration of alanine aminotransferase in serum.

measurement

Set of operations having the object of determining a value of a quantity.

measuring instrument

Device intended to be used to make measurements, alone or in conjunction with supplementary device(s).

measuring system

Complete set of measuring instruments and other equipment assembled to carry out specified measurements.
NOTE
Many anlalyzers used in clinical laboratory sciences are measuring systems.

method of measurement

Logical sequence of operations, describes generically, used in the performance of measurements.
EXAMPLE
Glucose oxydase/molecular absorption spectrometry method for the measurement of glucose concentration in serum.

metrology

Science of measurement.

minimum detectable value (of the net state variable)

True value of the net state variable in the actual state that will lead, with probability (1-b), to the conclusion that the system is not in the basic state.
NOTES
1. In clinical laboratory sciences the net state variable is conceptually equivalent to the state variable itself.
2. In clinical laboratory sciences and in analytical chemistry this concept is usually termed 'limit of detection'.

net state variable

Difference between the state variable and its value in the basic state.
NOTE
In clinical laboratory sciences the net state variable is conceptually equivalent to the state variable itself.

nonconformity

Nonfulfilment of a specified requirement

precision

Closeness of agreement between independent results of measurement obtained under stipulated conditions.
NOTES
1. Precision is a qualitative concept. Its quantitative counterpart is imprecision, which is computed as a standard deviation or a coefficient of variation of the measurement results.
2. Imprecision depends critically on the specified conditions.
3. Standard deviation expressing imprecision may depend on the value of the measurand; the phenomenon is called heteroscedasticity.

primary standard

Standard that is designated or widely acknowledged as having the highest metrological qualities and whose value is accepted without reference to other standards of the same quantity.

principle of measurement

Scientific basis of a measurement.
EXAMPLES
1. Molecular absorption spectrometry.
2. Chemiluminescence.

process in control

Process in which each of the quality measures is in a state of statistical control.

process quality control

That part of the quality control that is concerned with maintaining process variability within the required limits.

quality

Totality of features and characteristic of a product, process or service that bear on its ability to satisfy stated or implied needs.

quality assurance

All those planned and systematic actions necessary to provide adequate confidence that a product, process or service will satisfy given requirements for quality.

quality control

Operational techniques and activities that are used to fulfil given requirements for quality.

quantity

Attribute of a phenomenon, body or substance that may be distinguished qualitatively and determined quantitatively.
NOTES
1. The term 'quantity' may refer to a quantity in a general sense or to a particular quantity.
2. IUPAC and IFCC recommend the term 'kind-of-quantity' instead of 'quantity in a general sense' for the field of clinical laboratory sciences.
EXAMPLES
1. Kind-of-quantities: substance concentration, catalytic concentration, number fraction.
2. Particular quantities: substance concentration of glucose in serum of a given patient at a given time, mass rate of protein excretion of a given patient at a given day.

random error

Result of a measurement minus the mean that would result from an infinite number of measurements of the same measurand carried out under repeatability conditions.
NOTES
1. Random error is equal to error of measurement minus systematic error.
2. In practice, random error may be estimated from twenty or more repeated measurements of a measurand under specified conditions.

reference material

Material or substance one or more of whose property values are sufficiently homogeneous and well established to be used for the calibration of an apparatus, the assessment of a measurement method, or for assigning values to materials.
NOTE
Some reference materials have properties which, because they cannot be correlated with an established chemical structure or for other reasons, cannot be measured by exactly defined physical and chemical procedures. Such materials include certain biological reference materials to which an arbitrary unit termed 'international unit' has been assigned by the World Health Organization.
EXAMPLES
1. Human serum SRM 909b from the National Institute of Standards and Technology.
2. Human prolactin IS 84/500 from the World Health Organization.

relative error

Error of measurement divided by a true value of the measurand.

repeatability (of results of measurements)

Closeness of the agreement between the results of successive measurements of the same measurand carried out under the same conditions of measurement.
NOTES
1. Repeatability is a qualitative concept. Its quantitative counterpart is standard deviation of repeatability or coefficient of variation of repeatability of the measurement results.
2. Repeatability may depend on the value of the measurand.

repeatability conditions

Conditions where independent results of measurements are obtained with the same measurement procedure in the same laboratory by the same operator using the same equipment within short intervals of time.

repeatability

Precision under repeatability conditions.

reproducibility (of results of measurements)

Closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement.
NOTES
1. The changed conditions may include: principle of measurement, method of measurement, observer, measuring instrument, reference standard, location, conditions of use, time.
2. The set of specified condition is termed 'reproducibility conditions'.
3. Reproducibility is a qualitative concept. Its quantitative counterpart is standard deviation of repeatability or coefficient of variation of repeatability of the measurement results.
4. Reproducibility may depend on the value of the measurand.

reproducibility conditions

Conditions where results of measurements are obtained on the same measurand in different laboratories with different conditions.
NOTE
The different conditions should be specified.

reproducibility

Precision under reproducibility conditions

result of a measurement

Value attributed to a measurand, obtained by measurement.
NOTE
A complete statement of the result of a measurement includes information about the uncertainty of measurement.

secondary standard

Standard whose value is assigned by comparison with a primary standard of the same quantity.

sensitivity

Change in the response of a measuring instrument divided by the corresponding change in the stimulus.
NOTES
1. The sensitivity may depend on the value of the stimulus.
2. Sensitivity is not synonym of minimum detectable value (limit of detection).
3. Nosographic sensitivity (also called 'diagnostic sensitivity') should be clearly differentiated from (metrological) sensitivity.

specification

Document that prescribes the requirements with the product, process or service has to conform.

standard (of measurement)

Material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit of measurement or one or more values of a quantity to serve as a reference.

standard uncertainty (of a measurement)

Uncertainty of the result of a measurement expressed as a standard deviation.

state of statistical control

State in which the variations among the observed sampling results can be attributed to a system of chance causes which does not appear to change with time.
NOTE
In clinical laboratory sciences "sampling results" are the results obtained with control materials.

state variable

Quantity describing the state of a system.
NOTE
State variable is conceptually the same that particular quantity.
EXAMPLE
Substance concentration of a component in serum.

statistical quality control

That part of quality control in which statistical techniques are used.

systematic error

Mean that would result from an infinite number of measurements of the same measurand carried out under repeatability conditions minus a true value of the measurand.
NOTES
1. Systematic error is equal to error of measurement minus random error.
2. Systematic error may be constant or proportional to the value of the measurand.
3. In practice systematic error is estimated from twenty or more repeated measurements of a measurand under specified conditions.
4. In many instances the systematic error is called 'bias', but the International Vocabulary of Basic and General Terms in Metrology only uses this term as a characteristic of a measuring instrument.
5. Systematic error is practically equivalent to the IFCC classical concept of "inaccuracy".

tolerance interval

Variate values between and including tolerance limits.

tolerance limits

Specified variate values giving upper and lower limits to permissible values.

traceability

Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties.

true value (of a quantity)

Value consistent with the definition of a given particular quantity.
NOTES
1. This is a value that would be obtained by a perfect measurement. True values are by nature indeterminate.
2. The indefinite article 'a', rather than the definite article 'the' is used in conjunction with 'true value' because there may be many values consistent with the definition of a given particular quantity.

trueness

Closeness of agreement between the mean obtained from a large series of results of measurement and a true value or a conventional true value.
NOTES
1. Trueness is a qualitative concept. Its quantitative counterpart is systematic error.
2. Trueness is practically equivalent to the IFCC classical concept of "accuracy".

uncertainty of measurement

Parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand.
NOTE
The parameter may be, for example, a standard deviation (or a given multiple of it), or the half-width of an interval having a stated level of confidence.

unit (of measurement)

Particular quantity, defined and adopted by convention, with which other quantities of the same kind are compared in order to express their magnitudes relative to that quantity.

value (of a quantity)

Magnitude of a particular quantity generally expressed as a unit of measurement multiplied by a number.

working standard

Standard that is used routinely to calibrate or check material measures, measuring instruments or reference materials.
NOTE
In clinical laboratory sciences a working standard is usually called 'calibration material' or simply 'calibrator'.