When is it obvious?


 Most of us agree that the fairest and more objective way to test if a treatment works is the randomised controlled trial (RCT). We may also agree that there are situations where a RCT is not feasible, practical or ethical, or situations where the effect is so obvious that you don’t need to test it. An example of this is the use of parachutes when jumping from an airplane.

There is a satirical systematic review published some years ago in the Christmas edition of the BMJ where authors mention that they could not find any RCTs that proved that parachutes work. Therefore, “there is no evidence” that they do. The review is a slap in the face for RCTs fanatics, but also raises a topic to discuss. It’s obvious that parachutes works, despite anecdotes of people surviving falls without them. But if we think about other interventions, when is it too obvious that we don’t need to test it?

In medicine, we have a few examples about obvious interventions that have not been tested with RCTs: epinephrin for cardiac arrest, epinephrin for anaphylaxis, insulin for diabetes. It’s obvious that they work, right? Then we have some examples of things that may appear obvious, such as the use of oxygen for myocardial infarction. It turns out that the few RCTs included in a systematic review show a trend that it may actually harm patients. At least one RCT is currently underway to find out the real effect. 

Which lead us to electric fans.

When I read that the authors of a systematic review did not find RCTs that tested if electric fans helped in heat waves, the first thing that popped into my mind was isn’t it obvious? And then, when I saw the news appearing everywhere, CBSScienceBlogNPR, I thought the same. It appears there are some observational studies that suggest electric fans, when used in temperatures above 95ºF (35ºC), may actually cause harm. The theory is that by feeling cool, the person may actually stop drinking enough fluids and dehydrate. In an interview, one of the authors says that if you place a fan near a window and it brings hot air from the outside, it would be harmful. But, isn’t it obvious? We who leave in the tropic do not use fans like that. It’s as simple as putting the fan in a cooler area of your room, not where it can suck hot air.

After thinking about the context, and discussing it with friends, colleagues and teachers, I began to understand the uncertainty the authors have. The question raises from developed countries, where people #’s behaviours# are not adapted to high temperatures and where heat waves can kill thousands. It’s obvious that you feel better if you are hot and turn on an electric fan. What the authors don’t think is obvious is the effect fans may have in dehydration and heat strokes in persons at high risk. But even if it’s a well thought hypothesis, it will be very hard to study with a RCT. Who would accept to be allocated to the control group (no electric fan)?

Truth is, even if things appear obvious, it is always worth to reflect, try to see if they really are, or if it is just an illusion. When is it so obvious that we don’t need to study it? I have no idea. Maybe someone could enlighten me. 


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