The general concept of validity was traditionally defined as "the degree to which a test measures what it claims, or purports, to be measuring" (Brown, 1996, p. 231).

the construct: media effects
(it exists in theory and has been known to exist in practice)

construct validity: the experiment demonstrates that a test is measuring the construct it claims to be measuring

looking to show that media effects is a construct that can be measured to affect public opinion

the construct validity of a test should be demonstrated by an accumulation of evidence

Content validity is achieved when an instrument has appropriate content for measuring a complex concept, or construct.

An instrument has high construct validity if there is a close fit between the construct it supposedly measures and actual observations made with the instrument. The question is: Do your measures get at--that is, actually measure--the construct or constructs you are studying? An instrument has high construct validity, in other words, if it allows you to infer that a unit of analysis (a person, a country, whatever) has a particular complex trait and if it supports predictions that are made from theory.