High levels of depression are often due to poor supervision. Poor supervisors are more common than good ones.
Here is my view about PhD supervision.

1. PhD supervisors generally have no training in supervision skills.
2. Some supervisors know their academic discipline but have not bothered to learn anything about what is required of a supervisor.
2. Many supervisors ignore university guidelines and good practice.
3. Supervisors often seem accountable to nobody.
4. Many universities do nothing about supporting poor supervisors.
5. Universities are full of clever people but few seem able to see the link between poor supervisors and low completion rates.
6. The better the supervision, the more likely you are to complete.