In one sense you’re of course right that correlations are all we have. I think the most basic thing is correlating with wealth, or other aspects of a livid env

In one sense you’re of course right that correlations are all we have. I think the most basic thing is correlating with wealth, or other aspects of a livid environment. “Urban life engenders both early smartphone acquisition and more mental issues (at least self reporting)” is one hypothesis. Another is “social network usage correlates to more mental issues, and having smartphones gives more access to this” (which is relevant! But should be checked. Is it the phone? Is it social networks?) The point being that you are trying to establish a causal narrative, and right now there’s not much to chew on. If we want to help children we should dig deeper to understand actual causes instead of simply reporting the horizontal lines we found.