This book describes the psychometric properties of the Diagnostic Reasoning Assessment The Diagnostic Reasoning Assessment assesses the level of expertise of the diagnostic reasoning process in graduate level nurse practitioner students during performance exams using standardized patients. NP students' performance was assessed by faculty raters and Standardized Patient raters using the Diagnostic Reasoning Assessment. Generalizability studies were performed for the Diagnostic Reasoning Assessment, SOAP Note Evaluation Tool and Script Con-cordance Test to determine the variance components of the three measures. Evidence for the construct validity of the Diagnostic Reasoning Assessment was examined by comparing correlations bet-ween the Diagnostic Reasoning Assessment and the two other instruments, the SOAP note evaluation tool and the Script Concordance Test. Based on the studies conducted there is support for the psycho-metric properties of the Diagnostic Reasoning Assessment.