A student?s standardized examination score and high school percentile rank are two intitative factors admission often uses to form a selection index, which is one of the main criteria used to make college admission decisions, especially in public universities. While the standardized scores are based on national examinations, the high school percentile rank is dependent on the quality of the student?s high school. We constructed a modified high school percentile rank variable, to take into account both high school percentile rank and the quality of the student?s high school. Using student data from the University of Illinois at Chicago, we showed a student?s modified high school percentile rank as a substantially better indicator for university success than other commonly used variables. Based on this result, we recommend the use of a different admission selection index; one based on a student?s standardized examination score and modified high school percentile rank. This new admission index should be used, together with other considerations such as diversity, to make better college admission decisions.