Decision-Making in Psychological Assessment

This chapter describes a number of factors that may influence a clinician's judgment and conclusions while conducting an assessment, and it discusses others that make interpretation of the results less than straightforward. It begins by discussing the effects of the prevalence, or base rate, of the disorder on the diagnostic accuracy of the findings. Even in the presence of seemingly unequivocal results pointing to a given diagnosis, the findings may lead to a false-positive conclusion if the prevalence is low and to a false-negative one if the prevalence is high. The chapter shows how using Bayes' theorem can tell us the likelihood of a wrong diagnosis. It next discusses incremental validity-whether adding another test to the battery increases diagnostic accuracy. If the new test is correlated with ones already administered, then the amount of new information it provides is limited and may increase unwarranted confidence in the final diagnosis. Third, the chapter discusses various biases and heuristics that may affect diagnostic decision-making, such as anchoring, diagnostic momentum, premature closure, and the influence of patient and assessor characteristics. It concludes by presenting a number of steps that should be taken to minimize the effects of these biases.