What is Validity
Validity indicates the degree to which a tool measures what it has been designed to measure. Assessing the validity of a psychological tool that measures abstract qualities (like intelligence or honesty) can be tricky. There are, however, a number of scientific methodologies that we use to answer the question "How well do our instruments measure what they are supposed to measure?"
Multiple Validation Methods
Our validity studies are conducted using statistical analysis of raw assessment data, one-on-one interviews with respondents, individual comparative survey questionnaires, and comparison of measurement to other validated comparable assessments in the marketplace.
Reliability indicates the consistency or stability of test performance and is one of the most important considerations when selecting tests and other assessment tools. A measure is said to have a high reliability if it produces similar results under consistent conditions.
Reliability does not imply validity. That is, a reliable measure that is measuring something consistently is not necessarily measuring what you want to be measuring. For example, while there are many reliable tests of specific abilities, not all of them would be valid for predicting, say, job performance. In terms of accuracy and precision, reliability is a more accurate way of describing precision, while validity is a more precise way of describing accuracy.
While reliability does not imply validity, a lack of reliability does place a limit on the overall validity of a test. A test that is not perfectly reliable cannot be perfectly valid, either as a means of measuring attributes of a person or as a means of predicting scores on a criterion. While a reliable test may provide useful valid information, a test that is not reliable cannot possibly be valid.