Validity
(1) An experimental designs: internal validity is the extent to which a study is free from design biases that threaten the interpretation of the results; external validity is the extent to which the results of the experiment generalise beyond the setting in which the study was conducted.
(2) In measurement: the extent to which an instrument measures what it is intended to measure. Validity is of three basic kinds:
- content,
- criterion-related,
- construct.