A fundamental requirement for neuropsychological assessment is dependability. Neuropsychological knowledge is dependable only if it has been validated using psychometric methods. Since batteries are used for interpretations, the psychometric validation methods that are acceptable for individual tests must be applied to batteries to produce dependable information. While the standardized battery has been validated, the flexible battery has not. Due to the probability that some tests will be impaired by chance, a flexible battery cannot produce dependable interpretations by selecting or combining test results. Localization and diagnostic assessments are obtained by comparisons. Comparisons require that the tests in a battery are invariant or have equivalent norms along with a common metric. While standardized batteries do meet these criteria, flexible batteries do not. Consequently, clinical judgment applied to a flexible battery cannot provide dependable knowledge beyond that which could be provided by a single validated individual test.