This isn't responsive to the parent's question, in a way that ironically underscores the point: you can tell me that "1 in 50 patients experience X", but that's meaningless, unless I know what X is in the selected population at baseline.
I don't mean to pick on you. This problem is widespread in academic research.
Care to share the meta-analysis? How does 1/39 compare to the base rate of those with severe depression who did not receive ECT?