Are the Findings Important?
Use common sense. A number of years ago NIH sponsored a study to determine whether patients with acute spinal injuries benefited from administration of large doses of steroids shortly after injury. A very carefully designed randomized clinical trial was done with very careful assessment of changes in sensory and motor function. In fact, the investigators were able to show that there was a statistically significant improvement in those who had received steroids. However, the differences were clinically minute. We're talking about maybe a centimeter or two more sensation in a patient who is basically a quadriplegic. So from a functional point of view the differences between the groups weren't of any consequence at all. To make matters worse, the patients who received high doses of steroids had a higher risk of pneumonia, so the steroids may have done more harm than good.
External Validity (Generalizability)
Can the conclusions of the study be generalized to other populations besides the study population? In other words, are the results externally valid?