To save a click: >Five hundred forty-eight undergraduates participated for course credit. [...] Our final sample consisted of 520 smartphone users. 520 isn't

To save a click: >Five hundred forty-eight undergraduates participated for course credit. [...] Our final sample consisted of 520 smartphone users. 520 isn't as bad as I was expecting, but it's still an order of magnitude away from being meaningful. And, obviously, a study population consisting only of students attending the same class is maybe going to be slightly biased.