Following my prior post, may I further ask about the conditions for causal inferences? Could you please kindly give me a clue, take an example of late-life depression and sleep disturbance.

With pleasure.

Thank you very much for the detailed reply.

Sure. First, there should be correlations between depression and sleep disturbance among older adults. Second, depression happens before sleep disturbance. Third, there is no other confounding factor that leads to sleep disturbance. If all three conditions are filled, then we can conclude that late-life depression leads to sleep disturbance. That’s my understanding.