Graduate studies, and in particular doctoral ones, pursue the development of scientific researchers able to make original contributions in a specific area of knowledge. However, attrition rates indicate that achieving this goal is not easy. The available evidence indicates that there are behavioral factors, positive and negative, that influence obtaining a doctoral degree. Unlike in other western nations, such as the USA, these factors have not been studied in Mexico. In particular, this article analyzes the relationship between academic success and the instruments commonly used to decide admission to undergraduate (EXANI-II) and postgraduate studies (EXANI-III) in Mexico. Additionally, a number of measurable psychological constructs are introduced. These constructs are different from those comprising the EXANI and can be used for admission to doctoral studies, to reduce attrition rates and increase the certainty about the timely completion of Doctoral dissertations.