I would say there is a great degree of variance when it comes to interviews. Each panel typically consists of two SMU faculty, a PS alumni, and a current PS student. While you should certainly be up to speed on the books and the topics you selected, make sure that it goes beyond summary–be able to address economic, ethical, political, philosophical, etc., ramifications. The books and topics are often a starting point for conversation–an ice breaker if you will. Sometimes the conversation will lead to interesting places and become the focus of the interview; sometimes the interview won’t even touch on the books and topics.