ABSTRACT
According to Merriam Webster (1996) evidence has different vernacular and legal meanings. In the vernacular it is associated with proof and truth, as well as the observation of events. In law, the term is more precise, referring to “proof of fact(s)” presented at a trial. Evidence is essential in convincing the judge or jury of the facts in a case, thereby enabling the discovery of truth. Legal evidence can include “hard” findings such as photographs, audio recordings, plaster castings, fingerprints, and medical records. More often, however, evidence is provided by a fallible witness who can be questioned and cross-examined. In this chapter we consider the evidentiary basis of psychological test data. Psychometric theory, the foundation of psychological test interpretation, evolved from statistical hypothesis testing (see chapter 3, this volume). Recent trends in test interpretation (see Chan, R.C.K., 2001; Martens, Donders, & Millis, 2001; Mitrushina, Boone & D’Elia, 1999; Putzke, Williams, Blutting, Konold, & Boll, 2001; and Rosenfeld, Sands & Van Gorp, 2000)
1This chapter is prepared with individuals who have received at least one undergraduate and one graduate course in statistics and psychometric theory in mind. Readers lacking this preparation, or those whose exposure to the topics is weak or dated, should review current works such as those prepared by Glenberg (1996) and Thorndike (1997). 2Please address correspondence to PO Box 246, Candor, NC 27229 or rdfphd@yahoo.com
champion interpretation anchored in base rate. Although base rate must be considered as an import component of diagnostic formulation, rarity is not synonymous with disability. For example, it is rare when children are born with extra digits or red eyes, but both are expressions of normal variation and rarely impair growth or development even though they may be associated with other disorders that affect development. In considering psychological findings as evidence it is wise to remember Fisher’s (1959) frequency admonition “…infrequency with which, in particular circumstances, decisive evidence is obtained, should not be confused with the force, or cogency, of such evidence” (p. 93).
