Correlation
or Causation – Developments in Medical Science
Like operations, medications and fad
diets, health care policy is usually appraised with a simple question: Does it
work, or doesn’t it? The assumption is that new regulations and practices
either cut costs and improve care, or they don’t; and so, by simple extension,
should be either supported or struck down.
Now a fascinating study asks
all of us to reconsider [how we
judge the success or failure of certain health care initiatives]. Focusing
on outcomes in obesity surgery, the study illustrates the breathtaking speed at
which clinical medicine can progress, [and
how wrong we can be about whether our medical initiatives are actually bringing
about improvements in patients’ lives.]
Doctors have attempted to use
surgery to treat obesity since the 1950s, but it wasn’t until the
early 1990s that doctors and patients began to view bariatric surgery [(stomach stapling, etc)] as an
acceptable alternative to diets, exercise and medications. Fuelled by dramatic
and well-televised outcomes, like patients clocking in losses of 100
pounds or more, the number of operations rose exponentially despite
the fact that they were still considered experimental and that complications
could be significant. Pulmonary embolism, leaks from the new intestinal
connections and even death were all known to result from bariatric surgery; and
the rates of such mishaps were not always systematically documented.
[As a result, in order to improve patient safety,] in 2006, the Centres for Medicare
and Medicaid Services (C.M.S) [(the
publicly funded health insurance programmes in the United States.)] began
restricting payment for bariatric surgery to so-called centres of
excellence. To become such a centre, hospitals needed first to fulfil criteria
set by one of two organizations, the American
[However,] in
the years since 2006, surgeons developed new operations, incorporated safer
techniques and better equipment, and began conducting large-scale
research on complication rates and safety measures [all of which would have improved the chances of successful surgery
for anyone, anywhere. This raises the question of whether we can be sure that
it was actually the decision to use only centres of excellence that led to the
improvements in survival rates, rather than these other improvements that would
have happened at any other hospital in the country?] Yes, Medicare patients
who had bariatric surgery after 2006 tended to do better, confirming
a common belief that the C.M.S. coverage decision contributed to the improvement
in outcomes and general upsurge in quality of care. But it wasn’t
clear if the improvements were due to the policy, or were simply a result
of the advances that had occurred over time.
To answer this question, the authors
of the new study reviewed the discharge records of more than 20,000 Medicare
patients who underwent bariatric surgery before and after the national coverage
decision. As with previous studies, they found that Medicare patients who had
their operations after 2006 did better than those who had them earlier.
The researchers then compared these
outcomes to those of patients who were not covered by Medicare and therefore
not restricted to having their operations done at centres of excellence. Even
after adjusting for individual patient risk factors and the specific type of
bariatric procedure performed, they found no differences in complication rates
or outcomes between Medicare and non-Medicare patients. Moreover, they
discovered that many of the improvements had been under way prior to
2006.
In other words, the much-heralded
policy of funnelling patients to centres of excellence has had little effect on
how patients do. [Thus this is a perfect
example of how something that looks like a case of causation (restricting
surgery to centres of excellence caused better results as patients suffered
fewer complications) was actually a case of correlation (restricting surgery to
centres of excellence just happened to coincide with a reduction in
post-operative complications) that was actually caused by something else. In
this case, the general improvement in surgical techniques in this field since
2006.]
The results of this study have
prompted the C.M.S. to reconsider its policy. As a number of patients who
may benefit from bariatric surgery do not currently choose to have it done
because of the difficulty of travelling to a centre of excellence for the
surgery and the subsequent regular medical check-ups
Not all bariatric surgeons
agree with lifting the 2006 coverage restrictions; but Dr. Dimick and his
co-authors believe that reviewing all the research and reassessing policy
choices is important, particularly in a field that has advanced as quickly as
theirs. “Policymaking has to be a dynamic process that reconsiders the evidence
as it comes out,” Dr. Dimick said. “If you’re going to keep designating centres
of excellence, you need to be sure they are actually excellent and actually
offering better care than other institutions.”
Dr. Pauline Chen, April 4th , 2013