One of the difficulties is that there are more than one source of measurement errors in performance assessment. Because of its vagueness and subjectivity, psychometricians have abandoned this concept for a long time. However, outside the measurement arena, face validity has come back in another form. The internal structure of things may not concur with the appearance. Many times professional knowledge is counter-common sense.
Content validity is concerned with sample-population representativeness .
For example, computer literacy includes skills in operating system, word processing, spreadsheet, database, graphics, internet, and many others. However, it is difficult, if not impossible, to administer a test covering all aspects of computing. Therefore, only several tasks are sampled from the population of computer skills. Content validity is usually established by content experts . Take computer literacy as an example again.