To judge these factors, readers need to consider the response rate. Having decided who the respondents represent, readers can proceed to making judgments about their responses. Validity is the degree to which a particular indicator measures what it is supposed to measure rather than reflecting some other phenomenon. At one extreme, readers can determine the extent to which researchers have compared the performance of their question with an external gold standard. Examples of criterion validity include comparing reported age with birth certificates, reported weight with measured weight, and reported eyesight with visual acuity.
Face validity has the disadvantage of being entirely subjective.
At the same time, it may be the only type of validity that can be applied to the important subjective questions that survey researchers are trying to answer. Construct Validity Construct validity is somewhere between criterion validity and face validity. The basic idea behind construct validity is that if your measurement does what you think it does, it should behave in certain ways. For example, the level of self reported pain would be expected to decrease when respondents are given morphine. Wherever possible, readers should look for evidence that the pattern of responses is generally what would be expected given other data.