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Musings about Clinical Prediction Rules

July 5, 2010 • Business • Larry Benz

Taking a mild break from blogging as I try to sift through and deal with CMS’ latest proposals to try and reduce physical therapy payments to about double the current minimum wage.  Am reposting some of our very early posts-this one from 25 April 2005.

I have been reading with great interest the posts which I believe correctly identify many of the issues we have within our profession from a public policy and research standpoint (e.g. the “commoditization” of PT and problems created by the variability in practice).  It is worth noting the great work that many of this blog’s authors have done in clincal prediction rules (CPR) and I believe that we must continue to develop more which would greatly decrease the variability in practice.  CPR’s work by directing us to a few directions which lead to the best results.  Counter-intuitively, less information can lead to better conclusions and better interventions.  There is some interesting references to this in some recent non-medical books as well as history.

A recent medical example comes from Malcom Gladwell’s new book, Blink.  He recounts the problem with the economically ridden Cook County ER and the struggle to correctly identify those patients that truly were at risk for heart attacks versus those that didn’t need the many resources often utilized for those potential patients.  Through collaboration, the well documented Goldman’s algorithm  was developed which combines the evidence of ECG with three urgent risk factors.  A decision tree then would recommend appropriate treatment options. ER physicians who didn’t use the algorithm for identification of urgent heart conditions but instead gathered a significant amount of information guessed right between 75 and 89 percent of the time.  The algorithm guessed right more than 95 percent of the time!  In most instances extra information isn’t an advantage and can lead you to the wrong path of intervention.  I believe that expert clinicians (who aren’t necessarily the most experienced) intuitively learn this.

I have read with interest the most recent Marcus Buckingham book, The One Thing You Need to Know which describes a similar phenomenon.  Although this book is about managing and leadership, Malcom describes his quest to find controlling insights-the crystallization of concept(s) that are so strong that they serve to be the best explanation (another words-the one thing).  For a concept to emerge as a controlling insight it must meet three requirements:  it must apply across a wide range of situations (how about diagnoses-LBP?), it must be a multiplier meaning that it will net the greatest return on investment of your time and energy (which specific signs and symptoms or special tests?), and lastly it must guide action (intervention).  I believe CPR’s should meet the same criteria.

Lastly, from medieval times, we have the rule of parsimony known as Occam’s Razor which essentially tells us that from a set of otherwise equivalent models-give us the simplest one!  This heuristic argument does not necessarily give correct answers; it is a loose guide to choosing the scientific hypothesis which (currently) contains the least number of unproven assumptions and is the most likely to be fruitful (in my military background they referred to this as the K.I.S.S. principle).  It has been stated that within contemporary medicine diagnostic parsimony advocates that when diagnosing a given injury, ailment, illness, or disease, one should strive to look for the fewest possible causes that will account for all of the symptoms.

Since this blog is about evidence, let’s learn from the references in BlinkBuckingham, and Occam and strive to develop and prove more CPR’s for physical therapy diagnosis and intervention.

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Larry Benz

Dr. Larry Benz, DPT, OCS, MBA, MAPP, is the Executive Chairman of Confluent Health. He is nationally recognized for his expertise in private practice physical therapy and occupational medicine. Dr. Benz’s current areas of interest include conducting research and integrating empathy, compassion, and positive psychology interventions within physical therapy. He released a book on September...

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