Re: Blaming the wrong tool
> Most Pokemon gyms & stops are at places where youths would normally congregate at anyway,
Do you have evidence to share with us that is the case?
> There's no real evidence other than just a random co-incidence unless the researcher has hard and fast evidence that the last app open on the unfortunate's mobile was indeed Pokemon Go.
That would only be true if _every_ place where youths normally congregate was also a Pokemon place.
Otherwise, you divvy up the location into the (for this case) 4 groups based upon combinations of two simple yes/no variables and ta-da you have controls against which your stats can be calculated. No need to look at the mobile phones.