Neuropsychological assessment is a difficult and complicated process. Often experienced clinicians as well as trainees and students gloss over fundamental problems or fail to consider potential sources of error. Since formal test data on the surface appear unambiguous and objective, they may fall into the habit of overemphasizing tests and their scores and underemphasizing all the factors that affect the validity, reliability and interpretability of test data. But interpretation is far from straightforward, and a pragmatic application of assessment results requires attention to a multitude of...