Cal Newport:

The data on the Reverse Flynn Effect includes several pieces of evidence that support Marriott’s claims. The IQ reversal, for example, seems to begin right around 2010—the point at which smartphones began their rapid ascent to ubiquity. In addition, according to the Northwestern study, the demographic suffering the steepest declines is 18 to 22-year-olds, who also happen to be the heaviest users of smartphones.