In my opinion, "setoff" refers to the group of people who used the Internet to do research before buying their cell phones.
Student or Learner
The overwhelming majority of cellphone users make the purchase in a store - some 78% do,with 12% buying online and 9% by some other means. Among the narrower setoff those who use the internet in their cellphone research,26% bought their device online.
The term "Setoff" as used by the text refers to witch of the followings..
I Can't Understand the exact meaning of setoff in the text !?