tudents in Ph.D. programs, or refuse to consider graduate credit older than ten years as counting towards a Ph.D. degree.  Similarly, students may be required to re-take the comprehensive exam if they do not defend their dissertations within five years of taking it. Overall, 57% of students who begin a Ph.D. program in the US will complete their degree within ten years, approximately 30% will drop out or be dismissed, and the remaining 13% of students will continue on past ten years.[23]Funding[සංස්කරණය]Doctoral students are usually discouraged from engaging in external employment during the course of their graduate training. As a result, Ph.D. students at U.S. universities typically receive a tuition waiver and some form of annual stipend. The source and amount of funding varies from field to field and university to university. Many U.S. graduate students work as teaching assistants or research assistants while they are doctoral students.  Graduate schools increasingly[තහවුරු කර නො