The data being used to back this is very much a "children" issue, a adolescent female issue to be exact. The rate of depression stated to skyrocket in 2012 for this specific group.

This also seems to be an obvious counter to the implied hypothesis that "rate of depression increases linearly with facebook usage" since they launched in like 2005 or so, grew steadily from at least 2007, and also have most likely seen a significant decline in usage among adolescents in the recent years.