Validity refers to the accuracy and validity of measurements or methods in research or other areas. It describes the extent to which a method or instrument actually captures the actual phenomenon that is to be measured or analysed.

In research, validity refers to whether a study actually investigates what it is supposed to investigate. For example, if a study is being conducted to investigate the effects of a drug treatment, the validity of the study is crucial to ensure that the results actually reflect the effects of the drugs and not other factors.

There are different types of validity, including internal validity, external validity, construct validity and ecological validity. Internal validity refers to the validity of study results within the study itself, while external validity refers to the transferability of results to other situations. Construct validity refers to whether a measurement instrument actually captures the construct it is intended to measure, and ecological validity refers to the transferability of the results to the real world.