Validity vs. Reliability. Do You Know the Difference?


April 2, 2015

screening imageWhile validity and reliability go hand in hand when it comes to personality assessment or other forms of employment testing, they do differ. Validity basically refers to research that provides evidence that a test actually measures what it is supposed to measure. Reliability is more of a consistency measure.

How reliable is it?

Consider this: You measured the length of your dining room table. It was 72 inches long. What if you measured it the next day and it was 68 inches? You would have to find out what went wrong with the measurement.  Did you use the tape measure incorrectly? Is your tape measure faulty? A reliable measure should yield the same result. If it did not we would say that the measure is unreliable.

So, similar to a pre-employment test, if, for example, if a person scores high in a trait such as dominance, that result should be the same if that same person takes the test six weeks later. If however, that same person scores low in dominance, you would have to conclude that the measure (or test) was inaccurate and unreliable and, therefore, of minimal value.

How valid is it?

Validity is the most important issue in selecting a test. It refers to what characteristic the test measures and how well the test measures that characteristic. It also tells you if the characteristic being measured by a test is related to job qualifications and requirements. Validity evidence indicates that there is linkage between test performance and job performance. It can tell you what you may conclude or predict about someone from his or her score on the test.

It is important to understand the differences between reliability and validity. Validity will tell you how good a test is for a particular situation; reliability will tell you how trustworthy a score on that test will be. You cannot draw valid conclusions from a test score unless you are sure that the test is reliable. Even when a test is reliable, it may not be valid. So, therefore you should be careful that any test you select is both reliable and valid for your situation.

When is a test both valid and reliable?

So while reliability and validity are closely inter-related, the distinct difference is best summed up with an example: A researcher devises a new test that measures IQ faster than the standard IQ test:

  • If the test delivers scores for a candidate of 82, 63, 141 and 100, then the test is not reliable or valid.
  • If the test consistently delivers a score of 99 when checked, but the candidates real IQ is 122, then the test is reliable, but not valid.
  • If the test delivers a consistent score of 118, then that is pretty close, and the test can be considered valid and reliable.
Topic: FAQ |