Why is validity important?
Validity has to do with the application of the test results; whether they are consistent with the evaluee’s actual ability and can predict how the evaluee will do on the job. Without validity, your results are not useful. It is possible to have reliability but not validity. In fact, this is the most important problem with many of the tests in use today, such as those that use isometric strength testing to predict lift capacity. There is a poor relationship between isometric strength and lift capacity. When I first started doing such testing many years ago, I was hopeful that it would be useful to predict lift capacity. Thus far, we have performed many such studies in our laboratory, with poor results, which is why I only endorse certain types of isometric testing. As an example, one of our studies (Matheson, LN, Danner, R, Grant, J, Mooney, V. Effect of computerized instructions on measurement of lift capacity: Safety, reliability, and validity. Journal of Occupational Rehabilitation,
