Doctoral programs have high dropout rates of 43% representing the highest among all post-baccalaureate programs. Cross sectional studies of doctoral students' retention have showed the importance of financial aid in predicting degree completion. These studies however, do not estimate the labor market's effect on doctoral student retention and neglect the longitudinal nature of doctoral study and the multiple requirements that make doctoral education a three-stage process. This research study examines the effect of various factors, including financial aid and labor market conditions, on the likelihood that doctoral students will complete the three stages of doctoral education: transition, development, and research. The results show that although financial aid as a whole is important, the type of financial aid received is even more significant and has differential impacts on doctoral students' retention at each stage. The study concludes that research assistantships have the highest likelihood of degree completion compared to students with other forms of financial support. Labor market conditions are also an important factor affecting doctoral student retention with higher expected earnings motivating doctoral students in the later part of their programs to complete their degrees.