Feb 17 2010

Choosing Your Evidence

The current process of districting in this country has many critics. Essentially their point is that congressmen carve up districts in odd ways so as to create an artificial majority for their party in their district. Of course, this leaves a majority for the other party in other districts, so everyone’s happy. This leads to the excessively high re-election rate in the House of Representatives of about 98%.

The best summary of this distorted practice in my opinion is by George Will, who says (and I paraphrase) – this is the practice of having politicians choose their voters rather than voters choosing their representatives.

There is a very similar phenomenon happening in the bizarro world of complementary and alternative medicine (CAM). CAM advocates seem intent on being able to choose their evidence, rather than have the scientific evidence choose which treatments are safe and effective.

This strategy is possible because there are many kinds of evidence in medicine. There is basic science dealing with biochemistry and physiology. There are observational studies that deal with observing what is happening in the world. And there are experimental studies where variables are carefully controlled and outcomes tracked. And within each category of scientific evidence there is a wide range of specific techniques and degrees of rigor.

If you take any topic in medicine that has been researched for years, you will likely find studies pointing in many different directions, with different inferences. Eventually we like to see that the majority of studies are pointing in a common direction, and it is this consensus of evidence that we base our opinions on. But there is almost always some disconfirming evidence, or studies that suggest a different interpretation.

As a result, if you choose which evidence to focus your attention, you can build a case for almost any conclusion you wish. This process is often called cherry-picking, and it is a common problem. It is also difficult to detect, unless you have a thorough knowledge of the relevant scientific evidence. Even then, it is a subtle mechanism by which bias asserts itself – for even if you look at all the evidence, knowing what relative weight to give to each kind of evidence requires expertise and judgment.

For example, advocates of science-based medicine (SBM) often refer to the plausibility of a claim or treatment. Plausibility generally refers to basic science evidence – does the alleged mechanism of a treatment make sense in light of what we know about physics, chemistry, and biology.

CAM advocates, however, often dismiss plausibility arguments as being “closed-minded” (an accusation which serves the same functional role as an accusation of lacking faith). To dismiss plausibility, however, is to dismiss a large segment of scientific evidence.

Anti-vaccinationists dismiss the extensive observational data showing no connection between vaccines and autism, and insist that the only relevant clinical evidence would be randomized experimental studies – which essentially cannot be done for ethical reasons.

Acupuncture advocates, meanwhile, dismiss randomized and blinded experimental studies that show acupuncture does not work, and prefer instead open-label “practical” studies which are almost guaranteed to give positive results.

Sometimes CAM advocates want to change the rules of evidence entirely. The existing rules do not give them enough elbow room – in other words, choosing the type of evidence to focus on still does not give them the results they want, they need to include low grade evidence as well. So they advocate specifically for allowing forms of evidence that are generally considered not scientific (like anecdotes), or only preliminary, and treating them as if they can be used to form clinical conclusions.

Further, they want to create a double-standard, where only CAM modalities are allowed to be based upon these unreliable or unscientific forms of evidence. In fact, the very label of CAM (or any of its variants) is designed to create such a double-standard.

SBM, on the other hand, advocates a single science-based standard for all health claims. Further, this standard is based upon an appropriate assessment of all scientific evidence, putting the different kinds of evidence into proper context.

Unfortunately, there is no simple formula for how to translate scientific evidence into clinical practice – this requires a nuanced understanding of the strengths and weaknesses of different kinds of evidence and how they apply to different kinds of questions. But there are many rules of thumb that the scientific community have developed over the last century – and it is largely these rules that CAM advocates wish to turn on their head.

Here are some examples: Basic science evidence is used to suggest new potential treatments, but those treatments still need to be subjected to clinical testing. Basic science also is a good indicator of plausibility, but plausibility is not sufficient. This can also be stated as – you cannot reliably extrapolate basic biochemical, physiological, or pharmacological phenomena into net clinical outcomes.

Basic science may also suggest that a treatment is implausible. While there is a base level of clinical evidence required to support even a highly plausible treatment, the more implausible a claim becomes the higher the bar should be raised for the level of clinical evidence required to conclude that it works none-the-less. For treatments that are highly implausible (homeopathy, say) the bar for clinical evidence should be raised high enough to counterbalance the basic science evidence that tells us it is implausible.


The reasons for exploring the complex issues surrounding the application of science to the practice of medicine is simple – we want to use treatments that are actually safe and effective. We want to know that a treatment really works, and does not just appear to work because of bias and self-deception.

I don’t think anyone can reasonably disagree with these goals. For health care professionals this is part of due diligence that is required, in my opinion, by professional ethics.

My core problem with CAM is that, in practice, it places allegiance to specific modalities above the interests of the patient, which require scientific due diligence. They do this largely by changing the rules of evidence so that they can choose, not the kinds of evidence that give us the most reliable information, but the kinds that tend to validate their preferred treatments.

This practice, which has been overtly adopted as CAM philosophy of medicine, functionally eliminates science as the basis for choosing treatments, since these practices allow anything under the umbrella of CAM. If homeopathy can get through the door, then anything can. And as further evidence of this my open challenge to name a CAM modality that has been rejected following negative scientific evidence remains unanswered.

More and more, as CAM culture becomes more sophisticated, this does not mean rejecting science, but changing the rules of science so that advocates can choose their evidence, rather than evidence choosing the treatments.

In that way CAM is more like politics than science.

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