Why clinicians often disagree about the validity of test results.

Examining the validity of test results using specialised methods is still a relatively new venture and many different approaches are taken to the same task. This paper discusses some of the reasons why discrepant results and differing conclusions may be arrived at by clinicians or researchers, depending on their theoretical and practical choices. These choices include whether to test for effort, what methods to use, how to employ effort tests, what failure criteria to apply and how to interpret individual results. Equally important is the decision about whether or not to employ effort testing to remove error from data in group research studies. No concensus has yet been reached on the need for systematic effort testing in group studies but there are indications that it should be a serious consideration because controlling for invalid data can lead to altered conclusions.