The Concise Data Processing Assessment (CDPA) was developed to probe student abilities related to the nature of measurement and uncertainty and to handling data. The diagnostic is a ten question, multiple-choice test that can be used as both a pre-test and post-test. A key component of the development process was interviews with students, which were used to both uncover common modes of student thinking and validate item wording. To evaluate the reliability and discriminatory power of this diagnostic, we performed statistical tests focusing on both item analysis (item difficulty index, item discrimination index, and point-biserial coefficient) and on the entire test (test reliability and Ferguson's delta). Scores on the CDPA range from chance (for novices) to about 80% (for experts), indicating that it possesses good dynamic range. Overall, the results indicate that the CDPA is a reliable assessment tool for measuring targeted abilities in undergraduate physics students. (Contains 4 tables and 10 figures.) [A 41-item list of references and notes is provided.]