Denialism

How we know what we know

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by

MarkH
in

Over the last few decades, the nature of medical knowledge has changed significantly. Before the revolution in evidence-based medicine, clinical medicine was practiced as more of an art (in the “artisan” sense). Individuals were treated empirically with a strong knowledge of medical biology, and the guidance of “The Giants”, or particularly skilled and respected practitioners. While the opinions of skilled practitioners is still valued, EBM adds a new value—one of “show me the evidence”.

Evidence-based medicine refers to the entire practice of gathering and applying medical knowledge. This includes evaluating diagnostic tests (e.g. how well does an CT scan diagnose pulmonary embolism?) and evaluating treatments (e.g. which anticoagulant is most effective, which one is safer, how long should you treat, etc.) There will always be some questions that are untestable, and some for which no testing is needed, and practices for which evidence is sketchy.

In corresponding with a friend recently, I started thinking about how we look at the quality of medical evidence, and how we can communicate this to the lay public.

Let’s take, for example, cholesterol.

It has been found over the years that there is a strong association between elevated cholesterol and coronary artery disease. Through many studies, it was found that LDL cholesterol is a useful marker of cardiac risk due to elevated cholesterol. Finally, it was found that lowering LDL cholesterol, especially with statin drugs, dramatically reduces heart disease risk and mortality.

That’s the facts. But what are they based on? How strong is the evidence?

Evidence-based medicine has many ways of grading quality of evidence. The primary reference for cholesterol treatment in the U.S. is the National Cholesterol Education Program’s Adult Treatment Panel III (NCEP and ATP III).

Before the report gets to any recommendations, it presents a table explaining how evidence used in the report is graded. First is the type of evidence (from randomized controlled trials down to clinical experience) then is the quality (from “very strong evidence” to “strong trend”).

For example, the ATP gives the following recommendation (among many):

Evidence statements: Secondary prevention trials demonstrate that reduction of LDL-cholesterol levels significantly reduces risk for recurrent major coronary events in persons with established CHD (A1).

That “A1” at the end gives an idea what kind of evidence we’re working with. In this case the statement is based on RCTs and there very strong evidence to support it.

Evidence-based medicine is about evidence. Sometimes that evidence is quite good, sometimes it isn’t: the quality of evidence is something we take into consideration when treating patients.

This is in stark contrast to so-called alternative medicine. Alternative medicine never discusses quality of evidence. The quality is usually, however, quite poor, relying on patient and physician anecdotes, uncontrolled “trials”, and fantasy.

Making use of EBM doesn’t have to be difficult. You don’t have to be able to interpret every chi-squared analysis, you don’t have to calculate every number needed to treat. You just have to be able to read the basic literature in your field, look up recommendations, and know how strong they are.

Anyone practitioner who ignores evidence-based medicine is not practicing the best of modern medicine. Anyone who treats disease without understanding the difference between evidence-based practice and non-evidence-based practice should hand you a Quack Miranda Warning when you walk in the door.

Comments

  1. bob koepp

    Evidence based medicine is a good ideal, but there are serious questions about how the idea is implemented. For example, available evidence doesn’t always speak to age-based or sex-based variations. And as we move into the brave new world of genetic- (or more generally, molecular-) based medicine, where individual variability is the name of the game, practicing evidence based medicine is going to require detailed knowledge not only of the science, but of individual patients. Medicine in the future is probably going to retain much of the “artisan model.”

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  2. Bill

    Evidence based medicine is fine, as far as it goes. But, far too often, profits trump evidence. Take dialysis, for example. The cost of treatment limits the standard treatment to 3 4 hour treatments per week when there is plenty of evidence that more treatments for longer times produce far better results.

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  3. PalMD

    That isn’t really an EBM question but a policy decision. EBM can give you an idea what does what, but it can’t decide how to use the knowledge.

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  4. William Wallace

    Medicine is still an art, and will always be, so long as humans remain human. But when humans become herds, chattel, or whatever, are are tantamount to this, well, then, we’ll ration medical treatment to maximize benefit and minimize cost.

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  5. Bill

    “we’ll ration medical treatment to maximize benefit and minimize cost.”

    That is close to what I was thinking, but rather than minimizing cost, most corporate entities (whether you are talking about large physicians groups or a pharmaceutical company)they want to maximize profits and provide safe, cookie cutter treatment. I know several individual doctors that are in such groups and privately will tell you they feel frustrated by this, but they do what they can, when they can.

    Like in my dialysis example, medicare doesn’t dictate treatment, they just set reimbursement. There are treatments that are far more effective than thrice weekly treatments and are actually profitable, if managed properly, but not nearly as profitable as PD or in center treatments. So, those remain the standard treatments.

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  6. Orac

    Evidence-based medicine is a step forward. However, one big drawback of EBM is that it comes very close to ignoring basic science and biological plausibility. Indeed, it ranks basic science considerations at the very bottom of its hierarchy of evidence. In the case of woo like homeopathy, that means, as far as EBM is concerned, a poorly done clinical trial that supposedly shows efficacy of homeopathy for a condition trumps all the basic science that says that homeopathic dilutions contain no active substance, that water does not have “memory” of active substance, that “like cures like” is not a valid scientific statement, etc., etc. It’s also why CAM practitioners can claim that unscientific modalities full of magical thinking have “evidence” that they work.

    That’s why Steve Novella coined a better term for what we as physicians should be practicing, “science-based medicine.” Think of it as EBM that takes into account scientific knowledge and prior probability based on our understanding of basic science. In reality, its main difference is that it allows us to consider basic science at a much higher level in the evidence hierarchy for treatments that are incredibly implausible on a strictly scientific basis in that for them to work much of what we know about various sciences would have to be seriously in error. Moadlities such as homeopathy or various “energy healing” modalities are good examples.

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  7. Bill

    So, in other words, if it smells like BS, it’s probably BS?

    Reply

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