An Unfounded Assumption About Practice Variation Finally Is Challenged

As I mentioned in a previous post, many people interpret the practice variation literature as demonstrating that physicians often make unsubstantiated, even irrational decisions for individual patients. This supposed irrationality is used as justification for all sorts of things.
For example, the latest issue of Health Affairs (not yet on the web) includes a key-note article by David Eddy, [Eddy DM. Evidence-based medicine: a unified approach. Health Aff 2005; 24-9-16], which asserted,

"In 1973 John Wennberg and his colleagues began to document wide variations in
practice patterns. The implications ... were undeniable: when different
physicians are recommending different things for essentially the same patients,
it is impossible to claim that they are all doing the right thing."

Wennberg studied, however, rates of particular management options in different geographic areas. He did not control for prevalence of disease in these areas (much less severity of disease, co-morbidity, patient's values, etc.) Therefore, it is going well beyond his data to say the physicians were recommending different things for essentially the same patients.
Eddy used this assertion, among others, to justify his idiosyncratic version of evidence-based medicine, which seems to put the interests of "society" in controlling costs and efficiency on par with, or perhaps above, what Eddy called "the narrow viewpoint of an individual physician and patient."
A new study in Medical Care strongly challenges this old, unfounded assumption about practice variation. (viewing online requires a subscription.) [Shwartz M, Pekoz EA, Ash AS et al. Do variations in disease prevalanece limit the usefulness of population-based hospitalization rates for studying variations in hospital admissions? Med Care 2004; 43: 4-11.]
Let me quote liberally from the accompanying editorial [Ashton CM, Pietz K. Setting a new standard for studies of geographic varation in hospital utilizaton rates. Med Care 2004; 43: 1-3]

"For decades researchers analyzing differences in area-specific hospital
utilization rates have worked under the assumption that adjusting geographic
areas for age and sex differences is sufficient to account for any geographic
differences in disease prevalence. Shwartz et al challenged that
assumption and have shown it to be untrue."
"What can be concluded from this research is that geographic differences in
disease prevalence rates exist, even in small geographic areas within a single
state, and that studies of geographic variation in hospitalization rates that
fail to take underlying disease prevalence into account run a serious risk of
coming to spurious conclusions. The findings of Shwartz et al have set a
new standard in variations research."

Congratulations to Shwartz et al for taking this one on. I don't deny that physicians may sometimes make less than optimal, and even irrational decisions. However, let's stop pillorying their decisions based on irrelevant practice variation data. And let's stop using practice variation data to justify putting more control in the hands of bureaucrats and managers who may not be more rational, and who have not taken an oath to put the interests of patients first.