Initially, graduate students usually rotate through the laboratories of several faculty researchers, after which the student commits to joining a particular laboratory for the remainder of his or her education. The remaining time is spent conducting original research under the direction of the principal investigator to complete and publish a dissertation. Unlike undergraduate and professional schools, there is no set time period for graduate education. Students graduate once a thesis project of significant scope to justify the writing of their dissertation has been completed, a point that is determined by the student's principal investigator as well as his or her faculty advisory committee. The average time to graduation can vary between institutions, but most programs average around 5–6 years.