  Over 1100 students over four semesters were given the option of taking an
introductory undergraduate statistics class either by in-person attendance in
lectures or by taking exactly the same class (same instructor, recorded
lectures, homework, blind grading, website, etc.) without the in-person
lectures. Roughly equal numbers of students chose each option. The online
lectures were available to all. Attendance by online students was rare. The
online students did slightly better on computer-graded exams. The causal effect
of choosing only online lectures was estimated by adjusting for measured
confounders, of which the incoming ACT math scores turned out to be most
important, using four standard methods. The four nearly identical point
estimates remained positive but were small and not statistically significant at
the 95% confidence level. Sensitivity analysis indicated that unmeasured
confounding was unlikely to be large but might plausibly reduce the point
estimate to zero. No statistically significant differences were found in
preliminary comparisons of effects on females/males, U.S./non-U.S. citizens,
freshmen/non-freshman, and lower-scoring/higher-scoring math ACT groups.
