I worked on the Suicide and Self Injury team at Facebook. It was multi faceted, and whilst out of the door escalations (to emergency services) is one metric, i

I worked on the Suicide and Self Injury team at Facebook. It was multi faceted, and whilst out of the door escalations (to emergency services) is one metric, it was a guardrail - i.e., if it went down it's likely something was wrong, not because "yay we solved suicide!". The more difficult thing is that sometimes it's not possible to develop a metric to properly capture "decreased risk of harm", and so proxy metrics have to be employed.