* Prior education: Students with a strong background in biology and related fields may progress faster.
* Research progress: The speed of research, including data collection and analysis, significantly impacts completion time. Some projects are inherently longer than others.
* Funding: Securing funding (e.g., fellowships, grants) can sometimes affect the pace of research, as funding limitations might necessitate adjustments in the research plan.
* University requirements: Each university has its own specific requirements and timelines for PhD programs.
* Individual student's pace: Some students work more quickly and efficiently than others.
Therefore, while 5-7 years is a common range, it's crucial to understand that it's an estimate, and individual experiences can differ significantly.