They build a succession of models each one in the sequence with more controls than the previous. As examples see tables B.6.1 and B.7.1. I think merit would fal

They build a succession of models each one in the sequence with more controls than the previous. As examples see tables B.6.1 and B.7.1. I think merit would fall under the 2nd model (SAT scores, academic index, GPA, ...).