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Posts tagged ‘regression to the mean’

POST HOC ERGO PROPTER HOC

¨After this, therefore because of this¨ – It´s a logical fallacy that we tend to make more often than we would like to admit. I already talked about this in one of my previous posts but I would like to explain it one more time by giving 2 examples.

A lot of people don´t know what a wonderful machine our body and mind is. It is by far the best thing you will own in your lifetime. For example, did you know that roughly 50% of all illnesses for which people seek medical help are ¨self limited¨, meaning they are cured by the body´s own healing processes without assistance from medical science. Let´s see a Porsche trying to fix a flat tire or a broken suspension……haven´t seen it yet. So the body, we can safely say, is a truly amazing machine with remarkable powers to set itself right.

With the body so effective in healing itself, many who seek medical assistance will experience a positive outcome even if the therapist or doctor does nothing. In other words, even a worthless treatment can appear effective, I mean we have a 50% change that our body will fix itself. So when an intervention is followed by improvement, the intervention is said to be ¨effective¨ according to the person´s experience. Now, don´t try to convince that person that maybe it may not have been the treatment that restored his health because he will not even listen to you, you have no chance. His ¨personal experience¨ tells him otherwise.  But what about if he would have tried another treatment or even no treatment at all? Maybe he would have learned something else. This is a classic example of  Post hoc ergo propter hoc.

Regression to the mean-  Many diseases are cyclical, meaning they get worse or better temporarily, but always move back to an average severity(1). Back pain, arthritis, allergies, and multiple sclerosis are cyclical, meaning sometimes they get worse and sometimes they get better. Usually, we go to the therapist or doctor when we have the most pain, so it´s bound to get better no matter what the therapist does to you (2). So as you can see this would be another classic example of post hoc ergo propter hoc.

Things are sometimes not  as clear as they appear and looking at things from a different perspective can give us a better idea of what´s really going on.

References

  1. Streiner DL. Regression toward the mean: Its etiology, diagnosis, and treatment. Can J Psychiatry. 2001;46:72–76
  2. Ernst E, Simon S. Trick or Treatment ? Alternative medicine on trial. Transworld Publishers.London,UK.2008
  3. Gilovich Thomas. How we know what isn´t so.The free press. 1991
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