The main goal of this article was to refute such research. So, if you want to show that their methodologies are superior, I think that would be great. Also the

The main goal of this article was to refute such research. So, if you want to show that their methodologies are superior, I think that would be great. Also they were assessing efficiency, and since the cost component of efficiency (performance/cost) is measured as per-pupil spending, then we wouldn't get very useful results if performance=f(per-pupil spending).