Validity is the extent to which a test measures or predicts what it is supposed to. There are two types of validity such as, content validity and predictive validity. Content validity is the extent to which a test samples the behavior that is of interest. Predictive Validity is the success with which a test predicts the behavior it is designed to predict. While reliability is concerned with the accuracy of the actual measuring instrument or procedure, validity is concerned with the study's success at measuring what the researchers set out to measure. Criterion related validity, also referred to as instrumental validity, is used to demonstrate the accuracy of a measure or procedure by comparing it with another measure or procedure which has been demonstrated to be valid.




Sources:
Jonathan Howell, Paul Miller, Hyun Hee Park, Deborah Sattler, Todd Schack, Eric Spery, Shelley Widhalm, and Mike Palmquist. (2005). Reliability and Validity. Writing@CSU. Colorado State University Department of English. Retrieved [January 4] from http://writing.colostate.edu/guides/research/relval/.