How does the rate of hospitalizations prove anything? Perhaps a growing awareness of mental health made people who were eligibile for hospitalization seek medical care, whereas before they would not be hospitalized for lack of a diagnosis? Or perhaps the same awareness made teens enact the pathological behavior they learned about online, complete with self-harm and suicide atemtps?
Any measure you can think to track a condition that is defined, diagnosed and (especially) self-diagnosed subjectively, is by definition subjective.