Randomized clinical trials (RCTs) are the “gold standard” for medical studies. Nevertheless, even RCTs have their problems. An NBER working paper by Ludwig, Marcotte and Norberg points highlights some of these issues. The authors examine whether or not anti-depressants reduce suicide rates (they find that anti-depressants do reduce suicide rates).
Unfortunately, using data from RCTs will not give an accurate picture of an anti-depressant’s impact on suicide. For one, RCTs have relatively small sample sizes due to their expense. Since suicide occurs very infrequently, it will be difficult to pick up an statistically significant differences in suicide rates between the treatment and control groups. Secondly, people at high risk for suicide will likely be excluded from the RCT for ethical reasons. Thus, the RCT may have a sample which will under-represent individuals with suicidal tendencies.
- Ludwig J, Marcotte DE, Norberg K (2007) “Anti-depressants and Suicide” NBER Working Paper #12906.