Steroid treatment of croup: a silk purse from a sow’s ear
Clinical research — finding out which treatments help and which ones don’t (or even make the situation worse) — is tough research to do. In the laboratory a scientist can control conditions so that only one thing changes, isolating the effect of a particular thing. Clinical research is different because humans are complicated. The researcher tries to control the situation as much as possible, but ultimately she is comparing one dissimilar human to another one.
The result is that a lot of clinical studies, such as interventions in which researchers give patients this or that medicine and then try to find out if it worked, are underpowered. This means the studies aren’t powerful enough to answer the simple question: does this treatment help? Usually the reason for the lack of power is that, for all but situations that show extreme differences between the groups, you need a lot of patients in the study to demonstrate any difference. Sometimes this means researchers need to enroll thousands of patients in the study.
Recognizing this problem, the concept of “meta-analysis” was devised. The idea is that one can take a bunch of underpowered studies and lump the information together. This can create, in effect, a single study with enough power to answer the question. Critics compared meta-analysis to making a silk purse from a sow’s ear — trying to take a lot of poor studies and make a good study from them. This can be a problem. But if you’ve ever taken your child to the doctor for treatment of croup, you and your child have been the beneficiaries of what meta-analysis can accomplish.
Croup is caused by swelling of the airway from a virus (see the link above for details), and corticosteroid medicines reduce swelling. So it seemed logical to try them for croup. But although some of the early studies suggested steroids helped, they were all underpowered to answer the question for sure. Then somebody did a meta-analysis with the data and showed steroids probably helped. This information then led other researchers to spend the large amount of time and effort to do some fully-powered studies. The results? Steroids, by mouth, injection, or even inhaled, help relieve the symptoms of croup.
So in this case it was a silk purse all along.