In spring 2014, faculty from the City University of New York (CUNY) reported on a randomized controlled trial they conducted. The goal of the experiment was to determine whether community college students who assess into elementary algebra could be successful if they were placed directly into college-level statistics (with extra support). The experiment was conducted at three urban CUNY community colleges. At the time of their recruitment into the experiment, participants did not plan to major in a subject requiring college algebra. Students who assessed into elementary algebra and agreed to participate in the study were randomly assigned to one of three treatments: 1) traditional elementary algebra, 2) traditional elementary algebra with extra support in a weekly workshop, or 3) college-level statistics with extra support in a weekly workshop. To control for teacher effects, each faculty member in the study taught one section associated with each of the 3 treatments. All of the instructors were full-time math faculty, and at each of the three colleges, there were four sections of each treatment for a total of 36 sections across the colleges with 721 student participants. In a comparison of course pass rates (C or better), students placed directly into college-level statistics outperformed both elementary algebra treatment groups. What is the explanatory variable? what is the response variable? what is the confounding variable? is this an experiment or an observational study?