I have already mentioned the importance of psychological tests as major resources in assessing intellectual, cognitive, and psychological states. Clinical and forensic psychologists are the only professionals trained to administer, score, and interpret these tests. The standard of care is to use a battery of tests rather than a single measure to evaluate the client. The psychologist selects the tests he/she deems appropriate. Judgments are based upon the referral question and the expertise of the psychologist in the use of specific tests.

Now we evidence that psychological tests can be as valid as physical tests. In a recent article in the American Psychologist (2001), Meyer, Finn, Eyde, Kay, Moreland, Dres, Eisner, Krubaszyn, and Reed present comparisons of physical and psychological assessment validity coefficients. They point out, for example, that the ability to detect dementia with psychological tests is as good as with an MRI.

Validity scores for such commonly employed tests as the MMPI, the MCMI, and the TAT are essentially the same as commonly used physical tests such as mammography, electrocardiograms, MRI, and Pap smears. In common English, predicting positive or negative outcomes from psychological tests are about the same as predictions from common medical tests.

Psychological assessment requires a battery of tests because results of one test may be contradictory to another, not unlike physical tests. That is why assessments require a comprehensive battery including a thorough case history. Repeated assessments are also required to establish changes over time. It is also particularly valuable if pre-condition evaluations or baselines can be used to compare current functions. This is usually difficult to obtain with most psychological tests. The major exception is intellectual functioning. Most clients have had this type of assessment during their school years.