The experiment is based on Dartmouth College freshmen who are randomly assigned to dorms and roommates, implying that a roommate's background variables are uncorrelated with own background characteristics.
As a natural experiment, the results indicate that the coefficient on roommate GPA is 0.12 and significant. However, this freshman roommate effect on GPA disappears by senior year. Own senior year GPA is not correlated with freshman year roommates' senior year GPA. Additionally, the roommate's pre-enrollment intention to graduate with honors has a positive and statistically significant effect on GPA. Regarding the major choice, the data show that randomly assigned roommates have no effect on major. And regarding membership in a fraternity, if a freshman roommate joins a fraternity then he is 8% more likely to do so and 27% of the roommate pairs join the same house. Thus, roommate peer effects are important influences in freshman year GPA and in decisions to join social organizations. Roommate effects are not important in determining choice of major.