A new article in Psychological Assessment, “Quantifying Diagnostic Uncertainty Using Item Response Theory: The Posterior Probability of Diagnosis Index” by Oliver Lindhiem, David Kolko, and Lan Yu from the University of Pittsburg School of Medicine describes a novel method for helping the clinician to consider the degree of uncertainty associated with a psychiatric diagnosis in terms of probability. The Posterior Probability of Diagnosis Index (PPOD) was developed using Item Response Theory. The PPOD Index takes a Bayesian approach to diagnosis, which takes into consideration a patient’s profile of symptoms. The authors illustrate the use of the PPOD Index in a sample of 321 children and adolescents with symptoms of Oppositional Defiant Disorder. Their results suggest that the PPOD Index yields more refined, and perhaps more clinically useful, information about a particular patient than does a traditional symptom count by estimating the confidence with which a diagnostic threshold is met or exceeded.
Question for Comment: How might the PPOD Index move us closer to a personalized medicine approach in the Mental Health Field?