Validated diagnostic test for introductory physics course placement

Diagnostic tests for placing students into appropriate courses are commonly used in higher education math and science departments. We found no physics education research examining the validity of such exams, how well they are placing students into appropriate courses, and what guidance these exams can give for better focusing instruction. In this study, we present criteria by which to evaluate the validity and value of a diagnostic test, and we then apply these to the test developed for physics course placement at Stanford University. We examine the data collected from the first year in which all students intending to enroll in an introductory physics course were required to take the test and received an email suggesting which course would best match their level of preparation based on their score. We found that most students followed this advice. We also found that the diagnostic test score was a good predictor of performance in both the introductory physics course for physics majors and the course targeting science and engineering majors. It was not a good predictor of performance in two other courses, likely due to lack of alignment between course objectives and diagnostic measures. We found many individual questions which were particularly discriminating in predicting performance in the various courses, suggesting specific topics on which instruction should focus. We found that 27 of the 38 questions were predictive of performance in at least one of the courses studied, and only 8 questions that were not predictive of course performance or did not show any difference between students enrolled in different courses. These results provide evidence for the validity and usefulness of our diagnostic test, and we offer it to instructors at other institutions who might find it of value.

Figure 1

Histogram of diagnostic scores for students in the honors course (Phys 61), standard calculus-based course (Phys 41), calculus-based course for poorly prepared students (Phys 41E), and algebra-based course (Phys 21).

Figure 2

Student course grades (Phys 61 and Phys 21) or exam grades (Phys 41 and Phys 41E) as a function of diagnostic exam scores. Points in red are for Phys 41E (the calculus-based course for students with no prior physics), points in black are for Phys 21 (the algebra-based mechanics course), points in green are for Phys 41 (the calculus based course for scientists and engineers), and points in blue are for Phys 61 (the honors course for physics majors). We include ordinary least squares trend lines and associated standard errors to guide the reader’s eye.