It is important for researchers to use valid instruments for the conclusions they draw are based on the information they obtain using these instruments.
The term "validity," as used in research, refers to the appropriateness, meaningfulness, correctness, and usefulness of any inferences a researcher draws based on data obtained through the use of an instrument.
Content-related evidence of validity refers to judgments on the content and logical structure of an instrument as it is to be used in a particular study.
Criterion-related evidence of validity refers to the degree to which information provided by an instrument agrees with information obtained on other, independent instruments.
A criterion is a standard for judging; with reference to validity, it is a second instrument against which scores on an instrument can be checked.
Construct-related evidence of validity refers to the degree to which the totality of evidence obtained is consistent with theoretical expectations.
A validity coefficient is a numerical index representing the degree of correspondence between scores on an instrument and a criterion measure.
An expectancy table is a two-way chart used to evaluate criterion-related evidence of validity.
Reliability
The term "reliability," as used in research, refers to the consistency of scores or answers provided by an instrument.
Errors of measurement refer to variations in scores obtained by the same individuals on the same instrument.
The test-retest method of estimating reliability involves administering the same instrument twice to the same group of individuals after a certain time interval has elapsed.
The equivalent-forms method of estimating reliability involves administering two different, but equivalent, forms of an instrument to the same group of individuals at the same time.
The internal-consistency method of estimating reliability involves comparing responses to different sets of items that are part of an instrument.
Scoring agreement requires a demonstration that independent scorers can achieve satisfactory agreement in their scoring.
