If you, like me, would have had to watch people play Candy Crush on the Tube [= the London subway] on the way to work every morning for seven years, you would not ask.
I felt terribly sorry for that loss of GDP and decline in mean global IQ.
Why would playing Candy Crush on the subway have any impact on GDP or IQ? Sounds like a non sequitur.
The plebians should be doing business during their commute, never stop hustling! /s