 The outlet box is usually nailed to a stud, and you will find that 16 inches from the side of that outlet will be another stud. Now, most people are right-handed, so the boxes are nailed on the left-hand side of the stud, believe it or not, for receptacles. But if you're not sure, all you do is you pop the cover off of the receptacle, and you can stick a screwdriver in beside the box in the drywall. Not in the box, but...