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“Assument” – How confirmation bias relates to assessment

Definition: noun – an assessment (or lack of assessment) where the practitioner’s treatment decision is based on confirmation bias instead of objective findings.

March 8, 2022  By Ken V Ansell


One of the best things that experience can bring to your practice is that you have often encountered similar problems many times over the years. This can be extremely beneficial to the person on your table seeking a resolution to their problem. Your past experience can guide you to using specific techniques that you know have provided successful outcomes or have helped you achieve faster, longer lasting results. It can also help you avoid an approach that hasn’t worked as well in the past. However, it can also create a pitfall if you are not careful.

I want to share with you my experience in treating one woman – I’ll call her “Mary.” When she came in for her initial treatment, she had subjective complaints of a painful right shoulder with limited movement, pain along the medial border of the right scapula as well as sharp pain and tightness between the spine and the scapula. As we went through her history she stated it had started about four days earlier. There wasn’t a specific injury or activity that had brought it on, and she had no history of this in the past. She had more or less just woken up with it and the pain got worse throughout the rest of the day. She also complained of pain with a deep breath in, almost like there was a knife in her back. Her description was: “I thought I was having a heart attack, but it was on the wrong side.” After she was checked over and heart issues eliminated by her physician, she was given the diagnosis of upper back spasms and she booked an initial treatment with me.

Now, looking at the list of symptoms,  I am sure that many of you are doing exactly what I did and thought – rib problem. Going through my physical assessment she was tender at the 4th and 5th costovertebral joints, along the 4th /5th  intercostal, tightness in the pec minor, serratus anterior and associated intra-scapular musculature. Her restricted shoulder abduction and flexion complaints could also be expected with a costovertebral problem.

In retrospect, however, my assessment was quick, and not nearly as thorough as it should have been. I had assumed, based on the symptoms that presented, she had a costovertebral problem. I subsequently looked for the objective findings to confirm my assumption. The term that is used to describe this is “confirmation bias” – where there is a tendency to search for or interpret information in a way that confirms one’s preconceptions.


She was suffering from a costovertebral issue, her subjective symptoms and my objective findings confirmed it, and I treated her accordingly. Although I treated the problem I assessed, I completely missed an underlying subscapularis problem. My confirmation bias confirmed the costovertebral dysfunction that I was expecting to find and that was as far as I looked. It was the missed subscapularis issue creating an impaction of the glenohumeral joint that was the true reason for her shoulder symptoms. During her follow up treatment, the costovertebral dysfunction was improved but she was still suffering with her right shoulder complaints. After a more complete assessment, the dysfunction that I had initially missed became glaringly apparent.

Luckily, no negative results occurred from me missing the second component to her symptoms, but it really got me thinking. How often does this happen? Is this something that affects many different types of practitioners? Is this something that only happens as we gain years of experience to base our decisions around? Does it happen with new therapists coming right out of school with a high level of confidence? Unfortunately, I do not have the data to answer these questions but it definitely gives us something to think about the next time we do our assessment.

Another question I had was what is the best way to describe how confirmation bias relates to the effectiveness of our assessments? Since I couldn’t find the right word to describe what I was trying to say, I made one up. Here is where that new word comes into play: The terms assume and assessment became ASSUMEMENT.

Definition: noun – an assessment (or lack of assessment) where the practitioner’s treatment decision is based on confirmation bias instead of objective findings.

I think that term completely describes my initial assessment in Mary’s situation.

The lesson I learned from this is to never assume. The knowledge that is gained with your years of experience is invaluable. It appears that the challenge at hand is to not let confirmation bias get in your way of providing the best care you can. Let your assessment, not your assumement, guide you in determining the problem. Let your experience guide your treatment.

Ken V. Ansell, RMT, D.Ac., has been a massage therapist in Regina for over 24 years, obtaining his education from the Western College of Remedial Massage Therapies. He is a member of MTAS, the Provincial Medical Acupuncture Association and the Canadian Contemporary Acupuncture Association.

The original article was printed in the Summer 2019 edition of Massage Therapy Canada.
The original online post was published on June 27th, 2019. 

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