Because this was a study, the money spent has little to do with the individual subjects. If pollster calls me for a a national opinion poll I would rather be p

Because this was a study, the money spent has little to do with the individual subjects. If pollster calls me for a a national opinion poll I would rather be paid 1/1000 of whatever the budget was than answer the questions, but obviously my participation is more helpful overall. The goal was to identify what actually works, which is something you need to know before improving the situation. Paying a bad teacher more will not make the education provided any better (despite whatever the teacher's union says).