A sombre essay by Jonathan Haidt and Jean M. Twenge, two psychologists who have spent years studying the effect of smartphones and social media on our daily lives and mental health.

It’s been obvious for years that smartphones — and particularly social media apps — are having a devastating impact on teenagers.

This synchronized global increase in teenage loneliness suggests a global cause, and the timing is right for smartphones and social media to be major contributors. But couldn’t the timing just be coincidental? To test our hypothesis, we sought data on many global trends that might have an impact on teenage loneliness, including declines in family size, changes in G.D.P., rising income inequality and increases in unemployment, as well as more smartphone access and more hours of internet use. The results were clear: Only smartphone access and internet use increased in lock step with teenage loneliness. The other factors were unrelated or inversely correlated.

These analyses don’t prove that smartphones and social media are major causes of the increase in teenage loneliness, but they do show that several other causes are less plausible. If anyone has another explanation for the global increase in loneliness at school, we’d love to hear it.

Me too. The companies continually avoid this awkward topic on the grounds that there isn’t real causal evidence for the connection. Rather like the tobacco companies in the early days of medical concerns about lung cancer, or oil companies and evidence of climate change. See Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Global Warming by Erik Conway and Naomi Oreskes for the grisly detail.

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