Relationship between validity and reliability

Foxcroft, Paterson, le Roux & Herbst (2004, p.В 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. Items are chosen so that they comply with the test specification which is drawn up through a thorough examination of the subject domain. Before going to the final administration of questionnaires, the researcher should consult the validity of items against each of the constructs or variables and accordingly modify measurement instruments on the basis of SME's opinion.ДЄ test has content validity built into it by careful selection of which items to include (Anastasi & Urbina, 1997). Content related evidence typically involves a subject matter expert (SME) evaluating test items against the test specifications. A test with only one-digit numbers, or only even numbers, would not have good coverage of the content domain.

For example, a test of the ability to add two numbers should include a range of combinations of digits. For example, does an IQ questionnaire have items covering all areas of intelligence discussed in the scientific literature?Д¬ontent validity evidence involves the degree to which the content of the test matches a content domain associated with the construct. Content validity Д¬ontent validity 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.В 114). As such, experiments designed to reveal aspects of the causal role of the construct also contribute to constructing validity evidence. 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. They also include relationships between the test and measures of other constructs. Such lines of evidence include statistical analyses of the internal structure of the test including the relationships between responses to different test items. Д¬onstruct validity evidence involves the empirical and theoretical support for the interpretation of the construct. A measure of intelligence presumes, among other things, that the measure is associated with things it should be associated with ( convergent validity), not associated with things it should not be associated with ( discriminant validity). For example, the extent to which a test measures intelligence is a question of construct validity. Validity is important because it can help determine what types of tests to use, and help to make sure researchers are using methods that are not only ethical, and cost-effective, but also a method that truly measures the idea or constructs in question.Д¬onstruct validity refers to the extent to which operationalizations of a construct (e.g., practical tests developed from a theory) measure a construct as defined by a theory. This has the effect of making claims of 'scientific or statistical validity' open to interpretation as to what, in fact, the facts of the matter mean. This is why 'scientific or statistical validity' is a claim that is qualified as being either strong or weak in its nature, it is never necessary nor certainly true. By contrast, 'scientific or statistical validity' is not a deductive claim that is necessarily truth preserving, but is an inductive claim that remains true or false in an undecided manner. The conclusion of an argument is true if the argument is sound, which is to say if the argument is valid and its premises are true. In logic, validity refers to the property of an argument whereby if the premises are true then the truth of the conclusion follows by necessity.

The use of the term in logic is narrower, relating to the relationship between the premises and conclusion of an argument. It is generally accepted that the concept of scientific validity addresses the nature of reality in terms of statistical measures and as such is an epistemological and philosophical issue as well as a question of measurement. In psychometrics, validity has a particular application known as test validity: 'the degree to which evidence and theory support the interpretations of test scores' ('as entailed by proposed uses of tests'). face validity, construct validity, etc.) described in greater detail below. Validity is based on the strength of a collection of different types of evidence (e.g. The validity of a measurement tool (for example, a test in education) is the degree to which the tool measures what it claims to measure. The word 'valid' is derived from the Latin validus, meaning strong. Validity is the main extent to which a concept, conclusion or measurement is well-founded and likely corresponds accurately to the real world. Extent to which a measurement corresponds to reality

Relationship between validity and reliability