Monday, 7 February 2011

Disability and Range of Motion - Flipping the relationship

Relationships can often be interpreted the wrong way round. Here's a good example from lumbar spine disability.

Lumbar spine range of motion as a measure of physical and functional impairment: an investigation of validity.

The authors examined two different methods for determining lumbar spine ROM, suggested by the AMA to represent level of disability in those with CLBP. Poor ROM is interpreted as high disability.

So what they did was examine the relationships between ROM and disability as determined by a variety of measures including two questionnaire's and also a physical examination by the therapist.

Here's their conclusion
CONCLUSIONS: There was no evidence for a relationship between low back range of motion and impairment, and thus it would appear illogical to evaluate impairment in chronic low back pain patients using a spinal range of motion model when aiming to measure or compensate disability.
See the problem here?

They are correct, their data showed no relationship. The problem is that they draw the assumption that the criterion measure's are the ones they compared the ROM tests to.

The supposed 'criterion' measures they have used include two subjectively answered questionnaire's and a subjectively performed physical examination.

Lets flip it round this time.

We could consider that the opposite to their conclusion could also be drawn from the same data. It just depends on how you look at it.

If instead physical ROM is determined as the criterion measure then instead the conclusion might be that disability scores as indicated by the tests used does not accurately represent actual physical disability.

And thus we have another great example of bad science from the world of the lower back.

I would contend that a valid criterion measurement of disability must be physical and objective, not subjectively measured such as in questionnaire format. As such the second conclusion in my opinion is the more important especially in the context of clinical practice.


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