Was there One Distractor too Many?

A mathematics item on the SAT—the Rolling Circle Problem—was found to be faulty. This paper reports a detailed investigation into its mathematical and psychometric properties. In addition to examining performance of the item with more than 100,000 examinees, two small studies were performed with the aid of a physical model of the problem. It was found that the problem could be considered ambiguous due to the nonspecification of the frame of reference, but that almost no one noticed this lack.