Validity

Lead Author(s): Jeff Martin, MD

Types of Validity

There are two types of validity:

• Internal : Inference from the study sample to the source population.

• External : Inference from the study sample to other external populations.

Measures of Validity

Validity is measured in terms of sensitivity (ability to measure who HAS the characteristic: disease or exposure) and specificity (ability to measure who DOES NOT HAVE the characteristic: disease or exposure).

Importance of Validity

In terms of study validity, though, the key question is not when is the study being carried out, but:

• when were the measurements made and

• how good are they?

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