Finally, they compared the front-door predictions and back-door predictions to the results from the randomized controlled experiment that was run at the same time. The results were impressive. The estimates from the back-door criterion (controlling for known confounders like Age, Race, and Site) were wildly incorrect, differing from the experimental benchmarks by hundreds or thousands of dollars. This is exactly what you would expect to see if there is an unobserved confounder, such as Motivation. The back-door criterion cannot adjust for it.
