I am not going to give too much credence to one study, especially by Rolf Foruli. But I will say what I see around . There is plenty of mental illness among Jehovah's witnesses. In a congregation of 90 there are the following:
3 known to have bi-polar
1 schizophrenia
10 + suffering with some depressive mood disorder
I'll create my own study and say that there is just as much mental illness among the jdubs as anywhere else maybe more.
A number of years ago , I worked in service with a circuit overseer's wife who was advocating taking anti -depressants. I think she was taking them too. She freely shared that there were many sisters in the circuit who got along with medication.