Validity (statistics)
In science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...

 and statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

, validity has no single agreed definition but generally refers to the extent to which a concept, conclusion or measurement is well-founded and corresponds accurately to the real world. The word "valid" is derived from the Latin validus, meaning strong. The validity of a measurement tool (for example, a test in education) is considered to be the degree to which the tool measures what it claims to measure.

In psychometrics
Psychometrics is the field of study concerned with the theory and technique of psychological measurement, which includes the measurement of knowledge, abilities, attitudes, personality traits, and educational measurement...

, validity has a particular application known as test validity
Test validity
Test validity concerns the test and assessment procedures used in psychological and educational testing, and the extent to which these measure what they purport to measure...

: "the degree to which evidence and theory support the interpretations of test scores" ("as entailed by proposed uses of tests").

In the area of scientific research design
Research design
Research designs are concerned with turning the research question into a testing project. The best design depends on your research questions. Every design has its positive and negative sides...

 and experimentation, validity refers to whether a study is able to scientifically answer the questions it is intended to answer.

In clinical fields, the validity of a diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...

 and associated diagnostic tests may be assessed.

It is generally accepted that the concept of scientific validity addresses the nature of reality and as such is an epistemological and philosophical issue as well as a question of measurement
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...

. The use of the term in logic is narrower, relating to the truth of inferences made from premises.

Reliability and validity

Validity is often assessed along with reliability
Reliability (statistics)
In statistics, reliability is the consistency of a set of measurements or of a measuring instrument, often used to describe a test. Reliability is inversely related to random error.-Types:There are several general classes of reliability estimates:...

 - the extent to which a measurement gives consistent results.

An early definition of test validity identified it with the degree of correlation between the test and a criterion. Under this definition, one can show that reliability of the test and the criterion places an upper limit on the possible correlation between them (the so-called validity coefficient). Intuitively, this reflects the fact that reliability involves freedom from random error and random errors do not correlate with one another. Thus, the less random error in the variables, the higher the possible correlation between them. Under these definitions, a test cannot have high validity unless it also has high reliability. However, the concept of validity has expanded substantially beyond this early definition and the classical relationship between reliability and validity need not hold for alternative conceptions of reliability and validity.

Within classical test theory
Classical test theory
Classical test theory is a body of related psychometric theory that predict outcomes of psychological testing such as the difficulty of items or the ability of test-takers. Generally speaking, the aim of classical test theory is to understand and improve the reliability of psychological...

, predictive or concurrent validity (correlation between the predictor and the predicted) cannot exceed the square root of the correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....

 between two versions of the same measure — that is, reliability limits validity.

Construct validity

Construct validity
Construct validity
In science , construct validity refers to whether a scale measures or correlates with the theorized psychological scientific construct that it purports to measure. In other words, it is the extent to which what was to be measured was actually measured...

 refers to the extent to which operationalizations of a construct (e.g. practical tests developed from a theory) do actually measure what the theory says they do. For example, to what extent is an IQ questionnaire actually measuring "intelligence"?

Construct validity evidence involves the empirical and theoretical support for the interpretation of the construct. Such lines of evidence include statistical analyses of the internal structure of the test including the relationships between responses to different test items. They also include relationships between the test and measures of other constructs. As currently understood, construct validity is not distinct from the support for the substantive theory of the construct that the test is designed to measure. As such, experiments designed to reveal aspects of the causal role of the construct also contribute to construct validity evidence.

Convergent validity

Convergent validity
Convergent validity
Convergent validity, is the degree to which an operation is similar to other operations that it theoretically should also be similar to. For instance, to show the convergent validity of a test of mathematics skills, the scores on the test can be correlated with scores on other tests that are also...

 refers to the degree to which a measure is correlated with other measures that it is theoretically predicted to correlate with.

Discriminant validity

Discriminant validity
Discriminant validity
In psychology, discriminant validity tests whether concepts or measurements that are supposed to be unrelated are, in fact, unrelated.Campbell and Fiske introduced the concept of discriminant validity within their discussion on evaluating test validity. They stressed the importance of using both...

 describes the degree to which the operationalization does not correlate with other operationalizations that it theoretically should not be correlated with.

Content validity

Content or contents may refer to:* Contentment, a state of being* Content , the highest common factor of a polynomial's coefficients* Content , an additive real function defined on a field of sets...

 is a non-statistical type of validity that involves “the systematic examination of the test content to determine whether it covers a representative sample of the behavior domain to be measured” (Anastasi & Urbina, 1997 p. 114). For example, does an IQ questionnaire have items covering all areas of intelligence discussed in the scientific literature?

Content validity evidence involves the degree to which the content of the test matches a content domain associated with the construct. For example, a test of the ability to add two numbers should include a range of combinations of digits. A test with only one-digit numbers, or only even numbers, would not have good coverage of the content domain. Content related evidence typically involves subject matter experts (SME's) evaluating test items against the test specifications.

A test has content validity built into it by careful selection of which items to include (Anastasi & Urbina, 1997). Items are chosen so that they comply with the test specification which is drawn up through a thorough examination of the subject domain. Foxcraft et al. (2004, p. 49) note that by using a panel of experts to review the test specifications and the selection of items the content validity of a test can be improved. The experts will be able to review the items and comment on whether the items cover a representative sample of the behaviour domain.

Representation validity

Representation validity
Representation validity
Representation validity is concerned about how well the constructs or abstractions translate into observable measures. There are two primary questions to be answered:...

, also known as translation validity, is about the extent to which an abstract theoretical construct can be turned into a specific practical test

Face validity

Face validity
Face validity
Face validity is a property of a test intended to measure something. It is the validity of a test at face value. In other words, a test can be said to have face validity if it "looks like" it is going to measure what it is supposed to measure...

 is an estimate of whether a test appears to measure a certain criterion; it does not guarantee that the test actually measures phenomena in that domain. Indeed, when a test is subject to faking (malingering), low face validity might make the test more valid.

Face validity is very closely related to content validity. While content validity depends on a theoretical basis for assuming if a test is assessing all domains of a certain criterion (e.g. does assessing addition skills yield in a good measure for mathematical skills? - To answer this you have to know, what different kinds of arithmetic skills mathematical skills include ) face validity relates to whether a test appears to be a good measure or not. This judgment is made on the "face" of the test, thus it can also be judged by the amateur.

Face validity is a starting point, but should NEVER be assumed to be provably valid for any given purpose, as the "experts" have been wrong before—the Malleus Malificarum (Hammer of Witches) had no support for its conclusions other than the self-imagined competence of two "experts" in "witchcraft detection," yet it was used as a "test" to condemn and burn at the stake perhaps 100,000 women as "witches."

Criterion validity

Criterion validity
Criterion validity
A valid measure actually measures what it says it will measure. To define a measure as valid, one can assess different types of validity. The type of validity of measurement assessed depends on what the researcher wants to know...

 evidence involves the correlation between the test and a criterion variable (or variables) taken as representative of the construct. In other words, it compares the test with other measures or outcomes (the criteria) already held to be valid. For example, employee selection tests are often validated against measures of job performance (the criterion), and IQ tests are often validated against measures of academic performance (the criterion).

If the test data and criterion data are collected at the same time, this is referred to as concurrent validity evidence. If the test data is collected first in order to predict criterion data collected at a later point in time, then this is referred to as predictive validity evidence.

Concurrent validity

Concurrent validity
Concurrent validity
Concurrent validity is a parameter used in sociology, psychology, and other psychometric or behavioral sciences. Concurrent validity is demonstrated where a test correlates well with a measure that has previously been validated. The two measures may be for the same construct, or for different, but...

 refers to the degree to which the operationalization correlates with other measures of the same construct that are measured at the same time. Returning to the selection test example, this would mean that the tests are administered to current employees and then correlated with their scores on performance reviews.

Predictive validity

Predictive validity
Predictive validity
In psychometrics, predictive validity is the extent to which a score on a scale or test predicts scores on some criterion measure.For example, the validity of a cognitive test for job performance is the correlation between test scores and, for example, supervisor performance ratings...

 refers to the degree to which the operationalization can predict (or correlate with) other measures of the same construct that are measured at some time in the future. Again, with the selection test example, this would mean that the tests are administered to applicants, all applicants are hired, their performance is reviewed at a later time, and then their scores on the two measures are correlated.

Experimental validity

The validity of the design of experimental research studies is a fundamental part of the scientific method
Scientific method
Scientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence subject to specific principles of...

, and a concern of research ethics
Research ethics
Research ethics involves the application of fundamental ethical principles to a variety of topics involving scientific research. These include the design and implementation of research involving human experimentation, animal experimentation, various aspects of academic scandal, including scientific...

. Without a valid design, valid scientific conclusions cannot be drawn. There are several different kinds of experimental validity.

Conclusion validity

One aspect of the validity of a study is statistical conclusion validity
Statistical conclusion validity
Statistical conclusion validity refers to the appropriate use of statistics to infer whether the presumed independent and dependent variables covary...

 - the degree to which conclusions reached about relationships between variables are justified. This involves ensuring adequate sampling procedures, appropriate statistical tests, and reliable measurement procedures. Conclusion validity is only concerned with whether there is any kind of relationship at all between the variables being studied; it may only be a correlation.

Internal validity

Internal validity
Internal validity
Internal validity is the validity of inferences in scientific studies, usually based on experiments as experimental validity.- Details :...

 is an inductive
Inductive reasoning
Inductive reasoning, also known as induction or inductive logic, is a kind of reasoning that constructs or evaluates propositions that are abstractions of observations. It is commonly construed as a form of reasoning that makes generalizations based on individual instances...

 estimate of the degree to which conclusions about causal relationships can be made (e.g. cause and effect), based on the measures used, the research setting, and the whole research design. Good experimental techniques, in which the effect of an independent variable
Independent variable
The terms "dependent variable" and "independent variable" are used in similar but subtly different ways in mathematics and statistics as part of the standard terminology in those subjects...

 on a dependent variable is studied under highly controlled conditions, usually allow for higher degrees of internal validity than, for example, single-case designs.

Eight kinds of confounding
In statistics, a confounding variable is an extraneous variable in a statistical model that correlates with both the dependent variable and the independent variable...

 variable can interfere with internal validity (i.e. with the attempt to isolate causal relationships):
  1. History, the specific events occurring between the first and second measurements in addition to the experimental variables
  2. Maturation, processes within the participants as a function of the passage of time (not specific to particular events), e.g., growing older, hungrier, more tired, and so on.
  3. Testing, the effects of taking a test upon the scores of a second testing.
  4. Instrumentation, changes in calibration of a measurement tool or changes in the observers or scorers may produce changes in the obtained measurements.
  5. Statistical regression, operating where groups have been selected on the basis of their extreme scores.
  6. Selection, biases resulting from differential selection of respondents for the comparison groups.
  7. Experimental mortality, or differential loss of respondents from the comparison groups.
  8. Selection-maturation interaction, etc. e.g., in multiple-group quasi-experimental designs

Intentional validity

To what extent did the chosen constructs and measures adequately assess what the study intended to study?

External validity

External validity
External validity
External validity is the validity of generalized inferences in scientific studies, usually based on experiments as experimental validity....

 concerns the extent to which the (internally valid) results of a study can be held to be true for other cases, for example to different people, places or times. In other words, it is about whether findings can be validly generalized. If the same research study was conducted in those other cases, would it get the same results?

A major factor in this is whether the study sample (e.g. the research participants) are representative of the general population along relevant dimensions. Other factors jeopardizing external validity are:
  1. Reactive or interaction effect of testing, a pretest might increase the scores on a posttest
  2. Interaction effects of selection biases and the experimental variable.
  3. Reactive effects of experimental arrangements, which would preclude generalization about the effect of the experimental variable upon persons being exposed to it in non-experimental settings
  4. Multiple-treatment interference, where effects of earlier treatments are not erasable.

Ecological validity

Ecological validity
Ecological validity
Ecological validity is a form of validity in a research study. For a research study to possess ecological validity, the methods, materials and setting of the study must approximate the real-life situation that is under investigation. Unlike internal and external validity, ecological validity is not...

 is the extent to which research results can be applied to real life situations outside of research settings. This issue is closely related to external validity but covers the question of to what degree experimental findings mirror what can be observed in the real world (ecology = the science of interaction between organism and its environment). To be ecologically valid, the methods, materials and setting of a study must approximate the real-life situation that is under investigation.

Ecological validity is partly related to the issue of experiment versus observation. Typically in science, there are two domains of research: observational (passive) and experimental (active). The purpose of experimental designs is to test causality, so that you can infer A causes B or B causes A. But sometimes, ethical and/or methological restrictions prevent you from conducting an experiment (e.g. how does isolation influence a child's cognitive functioning?). Then you can still do research, but it's not causal, it's correlational. You can only conclude that A occurs together with B. Both techniques have their strengths and weaknesses.

The relationship of external and internal validity

On first glance, internal and external validity seem to contradict each other: To get an experimental design you have to control for all interfering variables. That's why you often conduct your experiment in a laboratory setting. While gaining internal validity (excluding interfering variables by keeping them constant) you lose ecological or external validity because you establish an artificial lab setting. On the other hand with observational research you can't control for interfering variables (low internal validity) but you can measure in the natural (ecological) environment, at the place where behavior normally occurs. However, in doing so, you sacrifice internal validity.

The apparent contradiction of internal validity and external validity is, however, only superficial. The question of whether results from a particular study generalize to other people, places or times arises only when one follows an inductivist research strategy
Empiricism is a theory of knowledge that asserts that knowledge comes only or primarily via sensory experience. One of several views of epistemology, the study of human knowledge, along with rationalism, idealism and historicism, empiricism emphasizes the role of experience and evidence,...

. If the goal of a study is to deductively test
Falsifiability or refutability of an assertion, hypothesis or theory is the logical possibility that it can be contradicted by an observation or the outcome of a physical experiment...

 a theory, one is only concerned with factors which might undermine the rigor of the study, i.e. threats to internal validity.

Diagnostic validity

In clinical fields such as medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....

, the validity of a diagnosis, and associated diagnostic tests or screening tests
Screening (medicine)
Screening, in medicine, is a strategy used in a population to detect a disease in individuals without signs or symptoms of that disease. Unlike what generally happens in medicine, screening tests are performed on persons without any clinical sign of disease....

, may be assessed.

In regard to tests, the validity issues may be examined in the same way as for psychometric tests as outlined above, but there are often particular applications and priorities. In laboratory
A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...

 work, the medical validity of a scientific finding has been defined as the 'degree of achieving the objective' - namely of answering the question which the physician asks. An important requirement in clinical diagnosis and testing is sensitivity and specificity
Sensitivity and specificity
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...

 - a test needs to be sensitive enough to detect the relevant problem if it is present (and therefore avoid too many false negative results), but specific enough not to respond to other things (and therefore avoid too many false positive results).

In psychiatry
Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...

 there is a particular issue with assessing the validity of the diagnostic categories
Classification of mental disorders
The classification of mental disorders, also known as psychiatric nosology or taxonomy, is a key aspect of psychiatry and other mental health professions and an important issue for consumers and providers of mental health services...

 themselves. In this context:
  • content validity may refer to symptoms and diagnostic criteria;
  • concurrent validity may be defined by various correlates or markers, and perhaps also treatment response;
  • predictive validity may refer mainly to diagnostic stability over time;
  • discriminant validity may involve delimitation from other disorders.

Robins and Guze proposed in 1970 what were to become influential formal criteria for establishing the validity of psychiatric diagnoses. They listed five criteria:
  • distinct clinical description (including symptom profiles, demographic characteristics, and typical precipitants)
  • laboratory studies (including psychological tests, radiology and postmortem findings)
  • delimitation from other disorders (by means of exclusion criteria)
  • follow-up studies showing a characteristic course (including evidence of diagnostic stability)
  • family studies showing familial clustering

These were incorporated into the Feighner Criteria and Research Diagnostic Criteria
Research Diagnostic Criteria
The Research Diagnostic Criteria are a collection of psychiatric diagnostic criteria published in late 1970s . As psychiatric diagnoses widely varied especially between the USA and Europe, the purpose of the criteria were allow diagnoses to be consistent in psychiatric research...

 that have since formed the basis of the DSM and ICD classification systems.

Kendler in 1980 distinguished between:
  • antecedent validators (familial aggregation, premorbid personality, and precipitating factors)
  • concurrent validators (including psychological tests)
  • predictive validators (diagnostic consistency over time, rates of relapse and recovery, and response to treatment)

Nancy Andreasen (1995) listed several additional validators — molecular genetics
Molecular genetics
Molecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...

 and molecular biology
Molecular biology
Molecular biology is the branch of biology that deals with the molecular basis of biological activity. This field overlaps with other areas of biology and chemistry, particularly genetics and biochemistry...

, neurochemistry
Neurochemistry is the specific study of neurochemicals, which include neurotransmitters and other molecules such as neuro-active drugs that influence neuron function. This principle closely examines the manner in which these neurochemicals influence the network of neural operation...

, neuroanatomy
Neuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...

, neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...

, and cognitive neuroscience
Cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...

 - that are all potentially capable of linking symptoms and diagnoses to their neural substrates.

Kendell and Jablinsky (2003) emphasized the importance of distinguishing between validity and utility
In economics, utility is a measure of customer satisfaction, referring to the total satisfaction received by a consumer from consuming a good or service....

, and argued that diagnostic categories defined by their syndromes should be regarded as valid only if they have been shown to be discrete entities with natural boundaries that separate them from other disorders.

Kendler (2006) emphasized that to be useful, a validating criterion must be sensitive enough to validate most syndromes that are true disorders, while also being specific enough to invalidate most syndromes that are not true disorders. On this basis, he argues that a Robins and Guze criterion of "runs in the family" is inadequately specific because most human psychological and physical traits would qualify - for example, an arbitrary syndrome comprising a mixture of "height over 6 ft, red hair, and a large nose" will be found to "run in families" and be "hereditary", but this should not be considered evidence that it is a disorder. Kendler has further suggested that "essentialist" gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

 models of psychiatric disorders, and the hope that we will be able to validate categorical psychiatric diagnoses by "carving nature at its joints" solely as a result of gene discovery, are implausible.

In the United States Federal Court System validity and reliability of evidence is evaluated using the Daubert Standard. Perri and Lichtenwald (2010) provide a starting point for a discussion about a wide range of reliability and validity topics in their analysis of a wrongful murder conviction.

July 2010, 34-45.

See also

  • Validity (logic)
    In logic, argument is valid if and only if its conclusion is entailed by its premises, a formula is valid if and only if it is true under every interpretation, and an argument form is valid if and only if every argument of that logical form is valid....

  • Validation (disambiguation)
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