1.11. A researcher is interested in the effect of attending…

1.11. A researcher is interested in the effect of attending private school (vs public school) on students’ test scores.  He is worried that the effect of school choice on test scores is confounded by a number of unobserved factors, such as parental ambition.  The researcher also believes that driving distance between home and the nearest private school is randomly distributed in the population and has no direct effect on test scores.  If we believe these assumptions, what technique should the researcher use to estimate the effect of school choice on test scores, and why?