# QA Glossary

This is the Glossary of QA Terms of the Quality Assurance Management Staff (QAMS) within the Office of Modeling, Monitoring Systems, and Quality Assurance in the EPA's Office of Research and Development. To use this service, simply "click" on a letter below that corresponds to the first letter of the term you are searching for. This will bring you to the section for that letter.[ A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z ]

Permission to publish provided by Fred Haeberer, QAMS, who maintains this QAMS Glossary as a working document. Questions or comments about these terms can be directed to Mr. Haeberer at 202-260-5785.

**Absolute
method**: a body of procedures and techniques for which
measurement is based entirely on physically defined, fundamental
quantities.
**Acceptable
quality level**: a limit above which quality is considered
satisfactory and below which it is not. In sampling inspection,
the maximum percentage of defects or failures that can be
considered satisfactory as an average.
**Acceptable
quality range**: the interval, between specified upper and
lower limits of a sequence of values, within which the values
are considered to be satisfactory.
**Acceptable
value**: an observed or corrected value that falls within
the acceptable range. See **Corrected value** and **Observed
value**.
**Acceptance
sampling**: the procedure of drawing samples from a lot
or population to determine whether to accept or reject a sampled
lot or population.
**Accepted
reference value**: a numerical quantity that serves as an
agreed-upon basis for comparison, and which is derived as:
l) a theoretical or established quantity based on scientific
principles, 2) an assigned value, based on experimental work
of some recognized organization, or 3) a consensus quantity
based on collaborative experimental work under the auspices
of a scientific or engineering group.
**Accreditation**:
a formal recognition that an organization (e.g., laboratory)
is competent to carry out specific tasks or specific types
of tests. See also **Certification**.
**Accreditation
criterion**: a requirement that a laboratory must meet to
receive authorization and approval to perform a specified
task.
**Accredited
laboratory**: a laboratory which has been evaluated and
given approval to perform a specified measurement or task,
usually for a specific property or analyte and for a specified
period of time.
**Accuracy**:
the degree of agreement between an observed value and an accepted
reference value. Accuracy includes a combination of random
error (precision) and systematic error (bias) components which
are due to sampling and analytical operations; a data quality
indicator. EPA recommends that this term not be used and that
precision and bias be used to convey the information usually
associated with accuracy. See **Precision** and **Bias**.
**Action limit**: See **Control limit**.
**Adjusted
value**: the observed value after adjustment for values
of a blank or bias of the measurement system.
**Aliquant**:
a subsample derived by a divisor that divides a sample into
a number of equal parts but leaves a remainder; a subsample
resulting from such a divisor. See **Subsample**.

**Aliquot**:
a subsample derived by a divisor that divides a sample into
a number of equal parts and leaves no remainder; a subsample
resulting from such a division. In analytical chemistry the
term aliquot is generally used to define any representative
portion of the sample.

**Alpha
error**: See **Type I Error**.

**Alternate
method**: any body of procedures and techniques of sample
collection and/or analysis for a characteristic of interest
which is not a reference or approved equivalent method but
which has been demonstrated in specific cases to produce results
comparable to those obtained from a reference method.

**Analysis
(chemical)**: the determination of the qualitative and/or
quantitative composition of a substance.

**Analyte**:
the substance, a property of which is to be measured by chemical
analysis.

**Analytical
batch**: a group of samples, including quality control samples,
which are processed together using the same method, the same
lots of reagents, and at the same time or in continuous, sequential
time periods. Samples in each batch should be of similar composition
and share common internal quality control standards.

**Analytical
blank**: See **Reagent blank**.

**Analytical
limit of discrimination**: See **Method detection limit**.

**Analytical
reagent (AR)**: the American Chemical Society's designation
for the highest purity of certain chemical reagents and solvents.
See **Reagent grade**.

**Arithmetic
mean**: the sum of all the values of a set of measurements
divided by the number of values in the set, usually denoted
by x-; a measure of central tendency. See **Measure of central
tendency**.

**Assignable
cause**: a factor or an experimental variable shown to significantly
change the quality of an effect or a result.

**Audit**:
a systematic evaluation to determine the conformance to quantitative
specifications of some operational function or activity. See
**Audit of data quality**, **Performance evaluation audit**,
and **Technical systems audit**, and also **Review**,
and **Management systems review**.

**Audit
of data quality (ADQ)**: a qualitative and quantitative
evaluation of the documentation and procedures associated
with environmental measurements to verify that the resulting
data are of acceptable quality.

**Audit
sample**: See **Performance evaluation sample**.

**Average**:
See **Arithmetic mean**.

**Background
level (environmental)**: the concentration of substance
in a defined control area during a fixed period of time before,
during or after a data gathering operation.

**Batch**:
a quantity of material produced or processed in one operation,
considered to be a uniform discrete unit.

**Batch-lot**:
the samples collected under sufficiently uniform conditions
to be processed as a group. See **Batch**, **Batch size**.

**Batch-sample**:
one of the samples drawn from a batch.

**Batch-size**:
the number of samples in a batch-lot.

**Beta error**: See **Type II Error**.

**Bias**:
the systematic or persistent distortion of a measurement process
which deprives the result of representativeness (i.e., the
expected sample measurement is different than the sample's
true value.) A data quality indicator.

**Blank
sample**: a clean sample or a sample of matrix processed
so as to measure artifacts in the measurement (sampling and
analysis) process.

**Blind
sample**: a subsample submitted for analysis with a composition
and identity known to the submitter but unknown to the analyst
and used to test the analyst's or laboratory's proficiency
in the execution of the measurement process. See **Double-blind
sample**.

**Bulk
sample**: a sample taken from a larger quantity (lot) for
analysis or recording purposes.

**Calibrant**:
See **Calibration standard**.

**Calibrate**:
to determine, by measurement or comparison with a standard,
the correct value of each scale reading on a meter or other
device, or the correct value for each setting of a control
knob. The levels of the calibration standards should bracket
the range of planned measurements. See **Calibration curve**.

**Calibration-check**:
See **Calibrate**.

**Calibration-check
standard**: See **Calibration standard**.

**Calibration
curve**: the graphical relationship between the known values
for a series of calibration standards and instrument responses.

**Calibration
drift**: the difference between the instrument response
and a reference value after a period of operation without
recalibration.

**Calibration
standard**: a substance or reference material used to calibrate
an instrument.

**Candidate
method**: a body of procedures and techniques of sample
collection and/or analysis that is submitted for approval
as a reference method, an equivalent method, or an alternative
method.

**Carrying-agent**:
any diluent or matrix used to entrain, dilute or to act as
a vehicle for a compound of interest.

**CAS#**:
Chemical Abstracts Service registry number of elements, chemical
compounds, and certain mixtures.

**Cause-effect
diagram**: a graphical representation of an effect and possible
causes. A popular one is the Ishikawa "fish bone diagram."

**Central
line**: the line on a control chart that represents the
expected value of the control chart statistic; often the mean.
See **Control chart**.

**Certification**:
the process of testing and evaluation against specifications
designed to document, verify, and recognize the competence
of a person, organization, or other entity to perform a function
or service usually for a specified time. See also **Accreditation**.

**Certification
of Data Quality**: the real-time attestation that the activities
of an environmental data collection operation's individual
elements (e.g., sampling design, sampling, sample handling,
chemical analysis, data reduction, etc.,) have been carried
out in accordance with the operation's requirements and that
the results meet the defined quality criteria.

**Certified
Reference Material (CRM)**: a reference material that has
one or more of its property values established by a technically
valid procedure and is accompanied by or traceable to a certificate
or other documentation issued by a certifying body. See **Certification**
and **Reference material**.

**Certified
value**: the reported numerical quantity that appears on
a certificate for a property of a reference material.

**Chain-of-custody**:
an unbroken trail of accountability that insures the physical
security of samples, data and records.

**Chance
cause**: an unpredictable, random determinant of variation
of a response in a sampling or measurement operation.

**Characteristic**:
See **Property**.

**Check
sample**: an uncontaminated sample matrix spiked with known
amounts of analytes usually from the same source as the calibration
standards. It is generally used to establish the stability
of the analytical system but may also be used to assess the
performance of all or a portion of the measurement system.
See also **Quality control sample**.

**Check
standard**: a substance or reference material obtained from
a source independent from the source of the calibration standard;
used to prepare check samples.

**Chi-square
test**: a statistical test of the agreement between the
observed frequency of events and the frequency expected according
to some hypothesis.

**Clean
sample**: a sample of a natural or synthetic matrix containing
no detectable amount of the analyte of interest and no interfering
material.

**Coefficient
of variation (CV)**: a measure of relative dispersion (precision.)
It is equal to the ratio of the standard deviation divided
by the arithmetic mean. See also **Relative standard deviation**.

**Collaborative
testing**: the evaluation of an analytical method by typical
or representative laboratories using subsamples prepared from
a homogeneous standard sample.

**Collocated
sample**: one of two or more independent samples collected
so that each is equally representative for a given variable
at a common space and time.

**Collocated
samplers**: two or more identical sample collection devices,
located together in space and operated simultaneously, to
supply a series of duplicate or replicate samples for estimating
precision of the total measurement system/process.

**Comparability**:
the degree to which different methods, data sets and/or decisions
agree or can be represented as similar; a data quality indicator.

**Completeness**:
the amount of valid data obtained compared to the planned
amount, and usually expressed as a percentage; a data quality
indicator.

**Component
of variance**: a part of the total variance associated with
a specified source of variation.

**Composite
sample**: a sample prepared by physically combining two
or more samples having some specific relationship and processed
to ensure homogeneity. See **Flow-proportioned sample**
and **Time-proportioned sample**.

**Confidence
coefficient**: the probability statement that accompanies
a confidence interval and is equal to unity minus the associated
type I error rate (false positive rate). A confidence coefficient
of 0.90 implies that 90% of the intervals resulting from repeated
sampling of a population will include the unknown (true) population
parameter. See **Confidence interval**.

**Confidence
interval**: the numerical interval constructed around a
point estimate of a population parameter, combined with a
probability statement (the confidence coefficient) linking
it to the population's true parameter value. If the same confidence
interval construction technique and assumptions are used to
calculate future intervals, they will include the unknown
population parameter with the same specified probability.
See **Confidence coefficient**.

**Control
chart**: a graph of some measurement plotted over time or
sequence of sampling, together with control limit(s) and,
usually, a central line and warning limit(s). See **Central
line**, **Control limit** and **Warning limit**.

**Control
limit**: a specified boundary on a control chart that, if
exceeded, indicates a process is out of statistical control,
and the process must be stopped, and corrective action taken
before proceeding (e.g., for a Shewhart- chart the control
limits are the mean plus and minus three standard deviations,
i.e., the 99.72% confidence level on either side of the central
line.)

**Control
sample**: See **Quality control sample** and **Check
sample**.

**Control
standard**: See **Check standard**.

**Controlled
variable**: a variable that is set at a pre-selected level
when a controlled experiment is conducted.

**Correlation**:
a measure of association between two variables. See also **Correlation
coefficient**.

**Correlation
coefficient**: a number between -1 and 1 that indicates
the degree of linearity between two variables or sets of numbers.
The closer to -1 or +1, the stronger the linear relationship
between the two (i.e., the better the correlation.) Values
close to zero suggest no correlation between the two variables.
The most common correlation coefficient is the product-moment,
a measure of the degree of linear relationship between two
variables.

**Critical-toxicity
range**: the interval between the highest concentration
at which all test organisms survive and the lowest concentration
at which all test organisms die within the test period.

**Daily
standard**: synonym for Calibration standard.

**Data**:
facts or figures from which conclusions can be inferred.

**Data
quality**: the totality of features and characteristics
of data that bears on their ability to satisfy a given purpose;
the sum of the degrees of excellence for factors related to
data.

**Data
quality indicators**: quantitative statistics and qualitative
descriptors that are used to interpret the degree of acceptability
or utility of data to the user. The principal data quality
indicators are bias, precision, accuracy, comparability, completeness,
and representativeness.

**Data
Quality Objective (DQO)**: qualitative and quantitative
statements of the overall level of uncertainty that a decision-maker
is willing to accept in results or decisions derived from
environmental data. DQOs provide the statistical framework
for planning and managing environmental data operations consistent
with the data user's needs.

**Data
reduction**: the process of transforming raw data by arithmetic
or statistical calculations, standard curves, concentration
factors, etc., and collation into a more useful form.

**Data
set**: all the observed values for the samples in a test
or study; a group of data collected under similar conditions
and which, therefore, can be analyzed as a whole.

**Datum**:
the singular of data. See **Data** and **Value**.

**Defensible**:
the ability to withstand any reasonable challenge related
to the veracity or integrity of laboratory documents and derived
data.

**Degrees
of freedom**: the total number of items in a sample minus
the number of independent relationships existing among them;
the divisor used to calculate a variance term; in the simplest
cases, it is one less than the number of observations.

**Dependent
variable**: See **Response variable**.

**Detection
limit (DL)**: the lowest concentration or amount of the
target analyte that can be determined to be different from
zero by a single measurement at a stated level of probability.
See **Method detection limit**.

**Determination**:
the application of the complete analytical process of measuring
the property of interest in a sample, from selecting or measuring
a test portion to the reporting of results. See **Test determination**.

**Diluent**:
a substance added to another to reduce the concentration and
resulting in a homogeneous end product without chemically
altering the compound of interest.

**Dilution
factor**: the numerical value obtained from dividing the
new volume of a diluted substance by its original volume.

**Document
control**: a systematic procedure for indexing documents
by number, date and revision number for archiving, storage,
and retrieval.

**Double-blind
sample**: a sample submitted to evaluate performance with
concentration and identity unknown to the analyst. See **Blind
sample**.

**Duplicate**:
an adjective describing the taking of a second sample or performance
of a second measurement or determination. Often incorrectly
used as a noun and substituted for "duplicate sample." Replicate
is to be used if there are more than two items. See **Replicate**.

**Duplicate
analyses or measurements**: the analyses or measurements
of the variable of interest performed identically on two subsamples
of the same sample. The results from duplicate analyses are
used to evaluate analytical or measurement precision but not
the precision of sampling, preservation or storage internal
to the laboratory.

**Duplicate
samples**: two samples taken from and representative of
the same population and carried through all steps of the sampling
and analytical procedures in an identical manner. Duplicate
samples are used to assess variance of the total method including
sampling and analysis. See **Collocated sample**.

**Dynamic
blank**: a sample-collection material or device (e.g., filter
or reagent solution) that is not exposed to the material to
be selectively captured but is transported and processed in
the same manner as the sample. See **Instrumental blank**
and **Sampling equipment blank**.

**Dynamic
calibration**: standardization of both the measurement and
collection systems using a reference material similar to the
unknown. For example, a series of air-mixture standards containing
sulfur dioxide of known concentrations could be used to calibrate
a sulfur dioxide bubbler system.

**Environmental
sample**: a sample of any material that is collected from
an environmental source.

**Environmentally
related measurement**: any assessment of environmental concern
generated through or for field, laboratory, or modelling processes;
the value obtained from such an assessment.

**Equivalent
method**: any method of sampling and/or analysis demonstrated
to result in data having a consistent and quantitatively known
relationship to the results obtained with a reference method
under specified conditions, and formally recognized by the
EPA.

**Error
(measurement)**: the difference between an observed or corrected
value of a variable and a specified, theoretically correct,
or true value.

**Error
function**: the mathematical relationship of the results
obtained from the measurement of one or more properties and
the error of the applied measurement process. See **Normal
distribution**.

**Experimental
variable**: See **Independent variable**.

**External
quality control**: the activities which are routinely initiated
and performed by persons outside of normal operations to assess
the capability and performance of a measurement process.

**False
negative decision**: See **Type II Error**.

**False
negative result**: estimating (incorrectly) that an analyte
is not present when it actually is present.

**False
positive decision**: See **Type I Error**.

**False
positive result**: estimating (incorrectly) that an analyte
is present when it is actually not present.

**Field
blank**: a clean sample (e.g., distilled water), carried
to the sampling site, exposed to sampling conditions (e.g.,
bottle caps removed, preservatives added) and returned to
the laboratory and treated as an environmental sample. Field
blanks are used to check for analytical artifacts and/or background
introduces by sampling and analytical procedures. See **Dynamic
blank** and **Sampling equipment blank**.

**Field
duplicates**: See **Duplicate sample**.

**Field
reagent blank**: See **Field blank**.

**Field
sample**: See **Sample**.

**Flow
rate**: the quantity-per-unit time of a substance passing
a point, plane, or space; for example the volume or mass of
gas or liquid emerging from an orifice, pump, or turbine or
moving through a point in a conduit or channel.

**Flow-proportioned
sample**: a sample or subsample collected from a fluid system
at a rate that produces a constant ratio of sample accumulation
to matrix flow rate.

**Fortify**:
synonym for Spike.

**Full-scale
response**: the maximum output of a measurement instrument
in a given range as displayed on a meter or scale.

**Functional
analysis**: a mathematical evaluation of each component
of the measurement system (sampling and analysis) in order
to quantitate the error for each component. A functional analysis
is usually performed prior to a ruggedness test in order to
determine those variables which should be studied experimentally.

**Geometric
mean**: the antilogarithm of the mean of the logarithms
of all the values in a set.

**Good
laboratory practices (GLP)**: either general guidelines
or formal regulations for performing basic laboratory operations
or activities that are known or believed to influence the
quality and integrity of the results.

**Goodness-of-fit**:
the measure of agreement between the data in a data set and
the expected or hypothesized values.

**Grab
sample**: a single sample which is collected at one point
in time and place.

**Gross
sample**: See **Bulk sample**.

**Homogeneity**:
the degree of uniformity of structure or composition.

**In-control**:
a condition indicating that performance of the quality control
system is within the specified control limits, i.e., that
a stable system of chance is operating and resulting in statistical
control. See **Control chart**.

**Independent
variable**: See **Controlled variable**.

**Inspection
criterion**: the specification(s) and rationale for rejecting
and accepting samples in a particular sampling plan.

**Instrument
blank**: a clean sample processed through the instrumental
steps of the measurement process; used to determine instrument
contamination. See **Dynamic blank**.

**Interference**:
a positive or negative effect on a measurement caused by a
variable other than the one being investigated.

**Interference
equivalent**: the mass or concentration of a foreign substance
which gives the same measurement response as one unit of mass
or concentration of the substance being measured.

**Interlaboratory
calibration**: the process, procedures, and activities for
standardizing a given measurement system to ensure that laboratories
participating in the same program can produce comparable data.

**Interlaboratory
method validation study (IMVS)**: the formal study of a
sampling and/or analytical method, conducted with replicate,
representative matrix samples, following a specific study
protocol and utilizing a specific written method, by a minimum
of seven laboratories, for the purpose of estimating interlaboratory
precision, bias and analytical interferences.

**Interlaboratory
precision**: a measure of the variation, usually given as
the standard deviation, among the test results from independent
laboratories participating in the same test.

**Interlaboratory
test**: a test performed by two or more laboratories on
the same material for the purpose of assessing the capabilities
of an analytical method or for comparing different methods.

**Internal
quality control**: See **Intralaboratory quality control**.

**Internal
standard**: a standard added to a test portion of a sample
in a known amount and carried through the entire determination
procedure as a reference for calibration and controlling the
precision and bias of the applied analytical method.

**Intralaboratory
quality control**: the routine activities and checks, such
as periodic calibrations, duplicate analyses and spiked samples,
that are included in normal internal procedures to control
the accuracy and precision of measurements.

**Intralaboratory
precision**: a measure of the method/sample specific analytical
variation within a laboratory; usually given as the standard
deviation estimated from the results of duplicate/replicate
analyses. See also **Standard deviation** and **Variance**.

**Laboratory
accreditation**: See **Accredited laboratory** and **Accreditation**.

**Laboratory
blank**: See **Reagent blank**.

**Laboratory
control sample**: See **Quality control sample**.

**Laboratory
duplicates**: synonym for Duplicate analyses.

**Laboratory
performance check solution**: a solution of method and surrogate
analytes and internal standards; used to evaluate the performance
of the instrument system against defined performance criteria.

**Laboratory
replicates**: See **Replicate analysis** or **measurement**.

**Laboratory
spiked blank**: See **Spiked laboratory blank**.

**Laboratory
spiked sample**: See **Spiked sample**.

**Laboratory
sample**: a subsample of a field, bulk or batch sample selected
for laboratory analysis.

**Least
squares method**: a technique for estimating model coefficients
which minimizes the sum of the squares of the differences
between each observed value and its corresponding predicted
value derived from the assumed model.

**Limit
of detection (LOD)**: See **Method detection limit**.

**Limit
of quantification (LOQ)**: the concentration of analyte
in a specific matrix for which the probability of producing
analytical values above the method detection limit is 99 percent.

**Linearity**:
the degree of agreement between the calibration curve of a
method and a straight line assumption.

**Lot**:
a number of units of an article or a parcel of articles offered
as one item; commonly, one of the units, such as a sample
of a substance under study. See **Batch**.

**Lot
size**: the number of units in a particular lot. See **Batch
lot** and **Batch size**.

**Lower
control limit**: See **Control limit**.

**Lower
warning limit**: See **Warning limit**.

**Management
systems review (MSR)**: the qualitative assessment of a
data collection operation and/or organization(s) to establish
whether the prevailing quality management structure, practices,
and procedures are adequate for ensuring that the type and
quality of data needed and expected are obtained. See **Review**
and **Audit**

**Matrix**:
a specific type of medium (e.g., surface water, drinking water)
in which the analyte of interest may be contained. See **Medium**.

**Matrix
spike**: See **Spiked sample**.

**Matrix
spike duplicate sample analysis**: See **Matrix**, **Duplicate
analysis** and **Spiked sample**.

**Maximum
contaminant level**: the highest permissible concentration
of a pollutant that may be delivered to any receptor.

**Maximum
holding time**: the length of time a sample can be kept
under specified conditions without undergoing significant
degradation of the analyte(s) or property of interest.

**Mean**:
See **Arithmetic mean**.

**Measurement
range**: the range over which the precision and/or recovery
of a measurement method are regarded as acceptable. See **Acceptable
quality range**.

**Measurement
standard**: a standard added to the prepared test portion
of a sample (e.g. to the concentrated extract or the digestate)
as a reference for calibrating and controlling measurement
or instrumental precision and bias.

**Measure
of central tendency**: a statistic that describes the grouping
of values in a data set around some common value (e.g., the
median, arithmetic mean, or geometric mean.)

**Measure
of dispersion**: a statistic that describes the variation
of values in a data set around some common value. See **Coefficient
of variation**, **Range**, **Variance** and **Standard
deviation**.

**Medium**:
a substance (e.g., air, water, soil) which serves as a carrier
of the analytes of interest. See **Matrix**.

**Medium
blank**: See **Field blank** and/or **Laboratory blank**.

**Median**:
the middle value for an ordered set of n values; represented
by the central value when n is odd or by the mean of the two
most central values when n is even.

**Method**:
a body of procedures and techniques for performing a task
(e.g., sampling, characterization, quantification) systematically
presented in the order in which they are to be executed.

**Method
blank**: a clean sample processed simultaneously with and
under the same conditions as samples containing an analyte
of interest through all steps of the analytical procedure.

**Method
check sample**: See **Spiked laboratory blank**.

**Method
detection limit (MDL)**: the minimum concentration of an
analyte that, in a given matrix and with a specific method,
has a 99% probability of being identified, qualitatively or
quantitatively measured, and reported to be greater than zero.
See **Detection limit**.

**Method
of least squares**: See **Least squares method**.

**Method
performance study**: See **Interlaboratory method validation
study**.

**Method
quantification limit (MQL)**: See **Limit of quantification**
and also **Method detection limit**.

**Minimum
detectable level**: See **Method detection limit**.

**Mode**:
the most frequent value or values in a data set.

**Multipoint
calibration**: the determination of correct scale values
by measuring or comparing instrument responses at a series
of standardized analyte concentrations; used to define the
range for generating quantitative data of acceptable quality.

**Noise**:
the sum of random errors in the response of a measuring instrument.

**Normal
distribution**: an idealized probability density function
that approximates the distribution of many random variables
associated with measurements of natural phenomena and takes
the form of a symmetric "bellshaped curve."

**Observation**:
a fact or occurrence that is recognized and recorded.

**Observed
value**: the magnitude of a specific measurement; a variable;
a unit of space, time or quantity; a datum. The observed value
is that reported before correction for a blank value. See
**Corrected value**.

**Outlier**:
an observed value that appears to be discordant from the other
observations in a sample. One of a set of observations that
appears to be discordant from the others. The declaration
of an outlier is dependent on the significance level of the
applied identification test. See also **Significance level**.

**Parameter**:
any quantity such as a mean or a standard deviation characterizing
a population. Commonly misused for "variable", "characteristic"
or "property."

**Percentage
standard deviation**: synonym for Relative standard deviation.

**Performance
evaluation audit**: a type of audit in which the quantitative
data generated in a measurement system are obtained independently
and compared with routinely obtained data to evaluate the
proficiency of an analyst or laboratory.

**Performance
evaluation sample (PE sample)**: a sample, the composition
of which is unknown to the analyst and is provided to test
whether the analyst/laboratory can produce analytical results
within specified performance limits. See **Blind sample**
and **Performance evaluation audit**.

**Population**:
all possible items or units which possess a variable of interest
and from which samples may be drawn.

**Precision**:
the degree to which a set of observations or measurements
of the same property, usually obtained under similar conditions,
conform to themselves; a data quality indicator. Precision
is usually expressed as standard deviation, variance or range,
in either absolute or relative terms. See also **Standard
deviation** and **Variance**.

**Preventative
maintenance**: an orderly program of activities designed
to ensure against equipment failure.

**Primary
reference standard**: See **Primary standard**.

**Primary
standard**: a substance or device, with a property or value
that is unquestionably accepted (within specified limits)
in establishing the value of the same or related property
of another substance or device.

**Probability**:
a number between zero and one inclusive, reflecting the limiting
proportion of the occurrence of an event in an increasingly
large number of identical trials, each of which results in
either the occurrence or nonoccurrence of the event.

**Probability
sampling**: sampling in which: (a) every member of the population
has a known probability of being included in the sample; (b)
the sample is drawn by some method of random selection consistent
with these probabilities; and (c) the known probabilities
of inclusion are used in forming estimates from the sample.
The probability of selection need not be equal for members
of the population.

**Procedure**:
a set of systematic instructions for performing an operation.

**Proficiency
testing**: a systematic program in which one or more standardized
samples is analyzed by one or more laboratories to determine
the capability of each participant.

**Property**:
a quality or trait belonging and peculiar to a thing; a response
variable is a measure of a property. Synonym for Characteristic.

**Protocol**:
a detailed written procedure for a field and/or laboratory
operation (e.g., sampling, analysis) which must be strictly
adhered to.

**Quality**:
the sum of features and properties/characteristics of a product
or service that bear on its ability to satisfy stated needs.

**Quality
assessment**: the evaluation of environmental data to determine
if they meet the quality criteria required for a specific
application.

**Quality
assurance (QA)**: an integrated system of activities involving
planning, quality control, quality assessment, reporting and
quality improvement to ensure that a product or service meets
defined standards of quality with a stated level of confidence.

**Quality
Assurance Narrative Statement**: a description of the quality
assurance and quality control activities to be followed for
a research project.

**Quality
Assurance Objectives**: the limits on bias, precision, comparability,
completeness and representativeness defining the minimal acceptable
levels of performance as determined by the data user's acceptable
error bounds.

**Quality
Assurance Program Plan (QAPP)**: a formal document describing
the management policies, objectives, principles, organizational
authority, responsibilities, accountability, and implementation
plan of an agency, organization or laboratory for ensuring
quality in its products and utility to its users.

**Quality
Assurance Project Plan (QAPjP)**: a formal document describing
the detailed quality control procedures by which the quality
requirements defined for the data and decisions pertaining
to a specific project are to be achieved.

**Quality
Circle**: a small group of individuals from an organization
or unit who have related interests and meet regularly to consider
problems or other matters related to the quality of the product
or process.

**Quality
control (QC)**: the overall system of technical activities
whose purpose is to measure and control the quality of a product
or service so that it meets the needs of users. The aim is
to provide quality that is satisfactory, adequate, dependable,
and economical.

**Quality
control chart**: See **Control chart**.

**Quality
control check sample**: See **Calibration standard**.

**Quality
control sample**: an uncontaminated sample matrix spiked
with known amounts of analytes from a source independent from
the calibration standards. It is generally used to establish
intralaboratory or analyst specific precision and bias or
to assess the performance of all or a portion of the measurement
system. See also **Check sample**.

**Quantitation
limits**: the maximum or minimum levels or quantities of
a target variable that can be quantified with the certainty
required by the data user.

**Random**:
lacking a definite plan, purpose or pattern; due to chance.

**Random
error**: the deviation of an observed value from a true
value, which behaves like a variable in that any particular
value occurs as though chosen at random from a probability
distribution of such errors. The distribution of random error
is generally assumed to be normal.

**Random
sample or subsample**: a subset of a population or a subset
of a sample, selected according to the laws of chance with
a randomization procedure.

**Random
variable**: a quantity which may take any of the values
of a specified set with a specified relative frequency or
probability. It is defined by a set of possible values, and
by an associated probability function giving the relative
frequency of occurrence of each possible value.

**Randomization**:
the arrangement of a set of objects in a random order, a set
of treatments applied to a set of experimental units is said
to be randomized when the treatment applied to any given unit
is chosen at random from those available and not already allocated.

**Randomness**:
a basic statistical concept and property implying an absence
of a plan, purpose or pattern, or of any tendency to favor
one outcome rather than another.

**Range**:
the difference between the minimum and the maximum of a set
of values.

**Raw
data**: any original factual information from a measurement
activity or study recorded in laboratory worksheets, records,
memoranda, notes, or exact copies thereof and that are necessary
for the reconstruction and evaluation of the report of the
activity or study. Raw data may include photographs, microfilm
or microfiche copies, computer printouts, magnetic media,
including dictated observations, and recorded data from automated
instruments. If exact copies of raw data have been prepared
(e.g., tapes which have been transcribed verbatim, dated,
and verified accurate by signature), the exact copy or exact
transcript may be substituted.

**Reagent
blank**: a sample consisting of reagent(s), without the
target analyte or sample matrix, introduced into the analytical
procedure at the appropriate point and carried through all
subsequent steps to determine the contribution of the reagents
and of the involved analytical steps to error in the observed
value.

**Reagent
grade**: the second highest purity designation for reagents
which conform to the current specifications of the American
Chemical Society Committee on Analytical Reagents.

**Records
system (or plan)**: a written, documented group of procedures
describing required records, steps for producing them, storage
conditions, retention period and circumstances for their destruction
or other disposition.

**Recovery
efficiency**: in an analytical method, the fraction or percentage
of a target analyte extracted from a sample containing a known
amount of the analyte.

**Reference
material**: a material or substance, one or more properties
of which are sufficiently well established to be used for
the calibration of an apparatus, the assessment of a measurement
method, or assigning values to materials.

**Reference
method**: a sampling and/or measurement method which has
been officially specified by an organization as meeting its
data quality requirements.

**Reference
standard**: See **Calibration standard**.

**Relative
standard deviation**: the standard deviation expressed as
a percentage of the mean recovery, i.e., the coefficient of
variation multiplied by 100.

**Reliability**:
the likelihood that an instrument or device will function
under defined conditions for a specified period of time.

**Repeatability**:
the degree of agreement between mutually independent test
results produced by the same analyst using the same test method
and equipment on random aliquots of the same sample within
a short period of time.

**Replicability**:
See **Repeatability**.

**Replicate**:
an adjective or verb referring to the taking of more than
one sample or to the performance of more than one analysis.
Incorrectly used as a noun in place of replicate analysis.
Replicate is to be used when referring to more than two items.
See **Duplicate**.

**Replicate
analyses or measurements**: the analyses or measurements
of the variable of interest performed identically on two or
more subsamples of the same sample within a short time interval.
See **Duplicate analyses** or **measurements**.

**Replicate
samples**: two or more samples representing the same population
characteristic, time, and place, which are independently carried
through all steps of the sampling and measurement process
in an identical manner. Replicate samples are used to assess
total (sampling and analysis) method variance. Often incorrectly
used in place of the term "replicate analysis." See **Duplicate
samples** and **Replicate analysis**.

**Representative
sample**: a sample taken so as to reflect the variable(s)
of interest in the population as accurately and precisely
as specified. To ensure representativeness, the sample may
be either completely random or stratified depending upon the
conceptualized population and the sampling objective (i.e.,
upon the decision to be made.)

**Representativeness**:
the degree to which data accurately and precisely represent
the frequency distribution of a specific variable in the population;
a data quality indicator.

**Reproducibility**:
the extent to which a method, test or experiment yields the
same or similar results when performed on subsamples of the
same sample by different analysts or laboratories.

**Response
variable**: a variable that is measured when a controlled
experiment is conducted.

**Result**:
the product of a calculation, test method, test or experiment.
The result may be a value, data set, statistic, tested hypothesis
or an estimated effect.

**Review**:
the assessment of management/operational functions or activities
to establish their conformance to qualitative specifications
or requirements. See **Management systems review** and
also, **Audit**.

**Risk**:
the probability or likelihood of an adverse effect.

**Risk
(statistical)**: the expected loss due to the use of a given
decision procedure.

**Robustness**:
(in)sensitivity of a statistical test method to departures
from underlying assumptions. See **Ruggedness**.

**Rounded
number**: a number, reduced to a specified number of significant
digits or decimal places using defined criteria.

**Routine
method**: a defined plan of procedures and techniques used
regularly to perform a specific task.

**Ruggedness**:
the (in)sensitivity of an analytical test method to departures
from specified analytical or environmental conditions. See
**Robustness**.

**Ruggedness
testing**: the carefully ordered testing of an analytical
method while making slight variations in test conditions (as
might be expected in routine use) to determine how such variations
affect test results. If a variation affects the results significantly,
the method restrictions are tightened to minimize this variability.

**Sample**:
a part of a larger whole or a single item of a group; a finite
part or subset of a statistical population. A sample serves
to provide data or information concerning the properties of
the whole group or population.

**Sample
data custody**: See **Chain-of-custody**.

**Sample
variance (statistical)**: a measure of the dispersion of
a set of values. The sum of the squares of the difference
between the individual values of a set and the arithmetic
mean of the set, divided by one less than the number of values
in the set. (The square of the sample standard deviation.)
See also **Measure of dispersion**.

**Sampling**:
the process of obtaining a representative portion of the material
of concern.

**Sampling
equipment blank**: a clean sample that is collected in a
sample container with the sample-collection device and returned
to the laboratory as a sample. Sampling equipment blanks are
used to check the cleanliness of sampling devices. See **Dynamic
blank**.

**Sampling
error**: the difference between an estimate of a population
value and its true value. Sampling error is due to observing
only a limited number of the total possible values and is
distinguished from errors due to imperfect selection, bias
in response, errors of observation, measurement or recording,
etc. See also **Probability sampling**.

**Scheduled
maintenance**: See **Preventative maintenance**.

**Screening
test**: a quick test for coarsely assessing a variable of
interest.

**Secondary
standard**: a standard whose value is based upon comparison
with a primary standard.

**Selectivity
(analytical chemistry)**: the capability of a method or
instrument to respond to a target substance or constituent
in the presence of nontarget substances.

**Sensitivity**:
capability of method or instrument to discriminate between
measurement responses representing different levels of a variable
of interest.

**Significance
level**: the magnitude of the acceptable probability of
rejecting a true null hypothesis or of accepting a false null
hypothesis; the difference between the hypothetical value
and the sample result.

**Significant
digit**: any of the digits 0 through 9, excepting leading
zeros and some trailing zeros, which is used with its place
value to denote a numerical quantity to a desired rounded
number. See **Rounded number**.

**Significant
figure**: See **Significant digit**.

**Single
operator precision**: the degree of variation among the
individual measurements of a series of determinations by the
same analyst or operator, all other conditions being equal.

**Site**:
the area within boundaries established for a defined activity.

**Span-drift**:
the change in the output of a continuous monitoring instrument
over a stated time period during which the instrument is not
recalibrated.

**Span-gas**:
a gas of known concentration which is used routinely to calibrate
the output level of an analyzer. See **Calibration check
standard**.

**Specimen**:
See **Sample**.

**Spike**:
a known mass of target analyte added to a blank sample or
subsample; used to determine recovery efficiency or for other
quality control purposes.

**Spiked
laboratory blank**: See **Spiked reagent blank**.

**Spiked
reagent blank**: a specified amount of reagent blank fortified
with a known mass of the target analyte; usually used to determine
the recovery efficiency of the method.

**Spiked
sample**: a sample prepared by adding a known mass of target
analyte to a specified amount of matrix sample for which an
independent estimate of target analyte concentration is available.
Spiked samples are used, for example, to determine the effect
of the matrix on a method's recovery efficiency.

**Spiked
sample duplicate analysis**: See **Duplicate analysis**
and **Spiked sample**.

**Split
samples**: two or more representative portions taken from
a sample or subsample and analyzed by different analysts or
laboratories. Split samples are used to replicate the measurement
of the variable(s) of interest.

**Standard
(measurement)**: a substance or material with a property
quantified with sufficient accuracy to permit its use to evaluate
the same property in a similar substance or material. Standards
are generally prepared by placing a reference material in
a matrix. See **Reference material**.

**Standard
addition**: the procedure of adding known increments of
the analyte of interest to a sample to cause increases in
detection response. The level of the analyte of interest present
in the original sample is subsequently established by extrapolation
of the plotted responses.

**Standard
curve**: See **Calibration curve**.

**Standard
deviation**: the most common measure of the dispersion or
imprecision of observed values expressed as the positive square
root of the variance. See **Variance**.

**Standard
material**: See **Standard (measurement)**, **Reference
material**.

**Standard
method**: an assemblage of techniques and procedures based
on consensus or other criteria, often evaluated for its reliability
by collaborative testing and receiving organizational approval.

**Standard
operating procedure (SOP)**: a written document which details
the method of an operation, analysis or action whose techniques
and procedures are thoroughly prescribed and which is accepted
as the method for performing certain routine or repetitive
tasks.

**Standard
reference material (SRM)**: a certified reference material
produced by the U.S. National Institute of Standards and Technology
and characterized for absolute content independent of analytical
method.

**Standard
reference sample**: See **Secondary standard**.

**Standard
solution**: a solution containing a known concentration
of analytes, prepared and verified by a prescribed method
or procedure and used routinely in an analytical method.

**Standardization**:
the process of establishing the quantitative relationship
between a known mass of target material (e.g., concentration)
and the response variable (e.g., the measurement system or
instrument response.) See **Calibration**, **Calibration
curve** and **Multipoint calibration**.

**Statistic**:
an estimate of a population characteristic calculated from
a data set (observed or corrected values), e.g., the mean
or standard deviation.

**Stratification**:
the division of a target population into subsets or strata
which are internally more homogeneous with respect to the
characteristic to be studied than the population as a whole.

**Stratified
sampling**: the sampling of a population that has been stratified,
part of the sample coming from each stratum. See **Stratification**.

**Stock
solution**: a concentrated solution of analyte(s) or reagent(s)
prepared and verified by prescribed procedure(s), and used
for preparing working standards or standard solutions.

**Subsample**:
a representative portion of a sample. A subsample may be taken
from any laboratory or a field sample. See **Aliquant**,
**Aliquot**, **Split sample** and **Test portion**.

**Surrogate
analyte**: a pure substance with properties that mimic the
analyte of interest. It is unlikely to be found in environmental
samples and is added to them for quality control purposes.

**Surveillance**:
the act of maintaining supervision of or vigilance over a
well-specified portion of the environment so that detailed
information is provided concerning the state of that portion.

**Synthetic
sample**: a manufactured sample. See **Quality control
sample**.

**Systematic
error**: a consistent deviation in the results of sampling
and/or analytical processes from the expected or known value.
Such error is caused by human and methodological bias.

**Systems
audit**: See **Technical systems audit**.

**Systems
error**: See **Total systems error**.

**Target**:
the chosen object of investigation for which qualitative and/or
quantitative data or information is desired, e.g., the analyte
of interest.

**Technical
systems audit**: a thorough, systematic on-site, qualitative
review of facilities, equipment, personnel, training, procedures,
record keeping, data validation, data management, and reporting
aspects of a total measurement system.

**Technique**:
a principle and/or the procedure of its application for performing
an operation.

**Test**:
a procedure used to identify or characterize a substance or
constituent. See **Method**.

**Test
data**: See **Data**.

**Test
determination**: See **Determination**.

**Test
method**: See **Method**.

**Test
portion**: a subsample of the proper amount for analysis
and measurement of the property of interest. A test portion
may be taken from the bulk sample directly, but often preliminary
operations, such as mixing or further reduction in particle
size, are necessary. See **Subsample**.

**Test
result**: a product obtained from performing a test determination.
See **Test determination**.

**Test
sample**: See **Test portion**.

**Test
specimen**: See **Test portion**.

**Test
unit**: See **Test portion**.

**Time-proportioned
sample**: a composite sample produced by combining samples
of a specific size, collected at preselected, uniform time
intervals.

**Total
Quality Management (TQM)**: the process whereby an entire
organization, led by senior management, commits to focusing
on quality as a first priority in every activity. TQM implementation
creates a culture in which everyone in the organization shares
the responsibility for continuously improving the quality
of products and services, (i.e., for "doing the right thing,
the right way, the first time, on time.") in order to satisfy
the customer.

**Total
measurement error**: the sum of all the errors that occur
from the taking of the sample through the reporting of results;
the difference between the reported result and the true value
of the population that was to have been sampled.

**Traceability**:
an unbroken trail of accountability for verifying or validating
the chain-of-custody of samples, data, the documentation of
a procedure, or the values of a standard.

**Treatment
(experimental)**: an experimental procedure whose effect
is to be measured and compared with the effect of other treatments.

**Trip
blank**: a clean sample of matrix that is carried to the
sampling site and transported to the laboratory for analysis
without having been exposed to sampling procedures.

**Tuning**:
the process of adjusting a measurement device or instrument,
prior to its use, to ensure that it works properly and meets
established performance criteria.

**Type
I error, (alpha error)**: an (incorrect) decision resulting
from the rejection of a true hypothesis. (A false positive
decision.)

**Type
II error, (beta error)**: an (incorrect) decision resulting
from acceptance of a false hypothesis. (A false negative decision.)

**Uncertainty**:
a measure of the total variability associated with sampling
and measuring that includes the two major error components:
systematic error (bias) and random error.

**Universe**:
See **Population**.

**Upper
control limit**: See **Control limit**.

**Upper
warning limit**: See **Warning limit**.

**User
check**: an evaluation of a written procedure (e.g., chemical
analysis method) for clarity and accuracy in which an independent
laboratory analyzes a small number of spiked samples, following
the procedure exactly.

**Valid
study**: a study conducted in accordance with accepted scientific
methodology, the results of which satisfy predefined criteria.

**Validated
method**: a method which has been determined to meet certain
performance criteria for sampling and/or measurement operations.

**Validation**:
the process of substantiating specified performance criteria.

**Value**:
the magnitude of a quantity. A single piece of factual information
obtained by observation or measurement and used as a basis
of calculation.

**Variable**:
an entity subject to variation or change.

**Variance**:
See **Sample variance**.

**Verifiable**:
the ability to be proven or substantiated.

**Warning
limit**: a specified boundary on a control chart that indicates
a process may be going out of statistical control and that
certain precautions are required. For example, for a Shewhart-
chart the warning limits are placed at plus and minus two
standard deviations of the mean (i.e., at the 95% confidence
interval.)

**Working standard**: See **Secondary standard**.

**Zero drift**: the change in instrument output over a stated time
period of nonrecalibrated, continuous operation, when the
initial input concentration is zero; usually expressed as
a percentage of the full scale response.