It's an excellent question.
A conservative estimate now, developed recently by Jim Heckman at the University of Chicago, estimates $8 saved for every dollar expended.
I will tell you one very interesting thing that Fraser Mustard has just done some research on. In all the studies that have been done so far, no one has factored in long-term health costs or mental health costs. When we factor in childhood depression, adolescent depression, and adolescent health problems, we estimate that the true cost may be double Heckman's estimates. It may be as much as $16.