EBM Episode 4: Lack of Causality
This is the fourth episode in our series on EBM. In it we look at a common criticism that is the lack of answers to "how" questions (e.g. "how did I get sick?" or "how does this medicine work?")
EBM is empirical, meaning it is based on experiments that show whether something works or not. It is not concerned with causality because of two main reasons. The first is that finding how something works doesn't change whether it works or not (e.g. penicillin was used for decades and saved millions of lives before we figured out the complete mechanism of action); the second is that knowing how something works, even if true, may distract from any harms it may also cause (e.g. we understood how PSA testing works when it was being recommended for use on every man over 50) but it took years to understand the harms of this practice.
It is true that understanding the mechanisms of action is not only interesting but also has applications in medicine. Drug discovery can be accelerated and improvements can be driven by an understanding of how therapies do or do not work. However, having a good explanation on why something should work, does not substitute checking that it actually does.