A friend sent me an item for the "Pollyanna Drum" file today. It's a study of mental health and the internet, and its basic insight is that internet penetration has been different in different countries. So if we track measures of mental health along with levels of internet usage, we should be able to tell if there's any correlation.
Short answer: There isn't.
What the study finds is that as internet usage goes up, so do life satisfaction, negative experiences, and positive experiences. However, the numbers are all so close to zero that there's really no measurable effect at all.
The study also looks at mental health vs. cell phone use and finds much the same thing. They found a possible small increase in life satisfaction in countries with more cell phones, but it was still nothing meaningful. The authors also find no particular differences between sexes or age groups.
I don't know how seriously to take this report. It compares countries, not individuals, and shows only the broad impact of "the internet" on a vague outcome (life satisfaction). Overall, I'd say it's suggestive, but not much more.
That said, it's yet another brick in the coffin of social media hysteria. The more research that gets done, the less there seems to be to it.
What it suggests is that conservatives have always been like this.
Unless I misread it, they only compared "between-countries"* in the appendix and the conclusions you're referencing with the chart is the aggregation of all the people of all the countries.
I think you're also overstating/misstating what the study's conclusions were. From their own paper, "We did not make the necessary strong assumptions required for identifying causal effects". What they claim is a weak association between the global population's increased use of the internet and mobile tech.
One last point: It's quite a stretch to make country-level, let alone global-level assumptions about aggregated data of this nature. The better observation would have been to measure the internet and mobile use differences against the levels of life satisfaction.**
*-- The primary focus of the study was on "within-countries" while the appendix tackled -- seemingly as an afterthought -- "between-countries".
** -- The means of measuring life satisfaction was through the response of the question: "Please imagine a ladder, with steps numbered from 0 at the bottom to 10 at the top. The top of the ladder represents the best possible life for you and the bottom of the ladder represents the worst possible life for you. On which step of the ladder would you say you personally feel you stand at this time?"
I constantly remind myself that nearly all of these social "science" studies are junk. As D_Ohrk_E1 points out, the "study" doesn't seem to actually address what the conclusion/headline implies. And the design is deeply questionable.
Not to mention all the indications of folks suffering harm through social media, simple addiction, and the like. I'd give this one a big "So what?"