Evidence-Based Assessment:
The practice of Evidence-Based Medicine (EBM) is described as the application of evidence gained from the scientific and research communities to medical practice (Guyatt & Rennie, 2002; Straus, Richardson, Glasziou, & Haynes, 2005). These EBM practices have long been established for treatment and therapeutic strategies, but are now being recommended to increase the efficacy of many other diagnostic methods and instruments resulting in a strategy of Evidence-Based Assessment, or EBA. In the mental health professions, many sources referring to EBA recommend that a particular treatment, intervention or assessment has some level of empirical evidence to support its use. In the medical sense, EBM is more specific to mean that the professionals have evaluated the scientific literature and reviewed the published findings of the statistical relationships between a given condition and an assessment measure, treatment or intervention. This is commonly recorded as the effect size of the relationship. These published effect sizes can be converted to useful metrics, such as sensitivity and specificity, which can then be easily converted into Diagnostic Likelihood Ratios, (DLR) (Straus, et al., 2005). The benefit of using likelihood ratios is that the clinician can build a predictive index by combining the results from multiple lines of evidence during assessment to better support treatment decisions. A similar approach in psychological assessment is referred to as incremental validity or the use of multiple measures in combination to add greater predictive power to a diagnosis and proposed treatment plan. Johnston and Murray (2003) emphasized the importance of incremental validity in the assessment of children for the presence of psychological disorders. These researchers describe incremental validity as the use of methods that add to the assessment process in such a way as to improve outcomes. Johnston and Murray emphasize the value and importance of selecting a highly objective criterion. As they put it, “Demonstrating incremental validity will always be easier when the criterion is objective, widely agreed on, and not confounded with the information used in prediction.” (p. 499).