Sunday, April 22, 2012

How to Interpret Medical News and Tests

     There have always been and will always be news articles and TV news stories about the results of medical tests. Some of these articles will quote (usually incompletely and incorrectly) from a study published in a refereed journal, some will quote from a talk given at a medical conference, and some will be derived from an interview with a doctor whose research has come to their attention. One major problem, of course, is that the non-scientist  has no way to judge the medical significance of such news reports, let alone whether or not the reported work fulfills certain basic requirements of scientific rigor. In this blog I will present some guidelines to help such readers and viewers evaluate the news report or interview.

     Firstly, there are no real secrets in medical treatments. Everyone publishes their research, and, if it is significant, tries to get on Oprah's show. Failing that, the PR department of their hospital will issue news releases to local and national newspapers and magazines as well as to the TV media. All of us would like to become famous, respected by our peers, and rich, no matter what our field of endeavor, and keeping our successes secret is not the proper avenue to achieve this. For instance in the field of cancer, each hospital has its weekly tumor board meeting where interesting, challenging or puzzling cases and/or results are presented and discussed. Then in most large cities there is a monthly oncology get-together. There also are quarterly meetings around the country as well as an annual meeting, which meeting is always well-attended by the media.

     Secondly, be careful about placing too much credence in any single report of a talk or paper delivered at a medical meeting. Such a report may or may not be clinically accurate, but until it is submitted for consideration to a refereed journal and is published, it is just one doctor's opinion. In my prior field of physics we recently had  newspaper reports of an experiment which purported to show that neutrinos traveled faster than the speed of light, but a careful re-analysis of the data showed that they did not.

     Third, it is essential to understand and appreciate the difference between relative risk and absolute risk. Absolute risk compares you to the entire world, e.g. you have a 10% chance of going bald if you are a man. Relative risk compares your subset to others in your group: if you are an American male, you have twice the chance of going bald than if you are Chinese. Researchers and reporters use relative risk to over-emphasize their results, and sometimes to stampede you into a certain behavior:  the relative risk number is always larger than the absolute risk number because a subset (the denominator in risk calculations) is always a smaller number than the entire set of humans. If your chance of being hit by lightning is 1/2,000,000, or one in two million, and I can reduce your risk to 1/1,000,000, the absolute statement is that I reduced your absolute risk by 1/1,000,000 , or 0.0001%. OTOH I can say with equal validity, that I reduced your relative risk by one-half, or 50%. Always look to see the absolute number, because only that number has immediate relevance to your case.

   Fourth, in connection with the degree of risk protection, we have the "number needed to treat", or NNT. That is, how many patients, based on the statistics of the study, would have to be treated by the drug or intervention in question in order to get one positive result (i.e. cure one patient, diagnose one disease, save one life, etc.). And note that they NEVER quote the NNS, or the number needed to treat to have one patient get  a side effect, and usually the NNS is quite smaller than the NNT. Would you take a pill to prevent a heart attack if they had to treat 10 people to save one person from a heart attack? What about 100, or 1,000, or 10,000 or 100,000? And would you still agree to treatment if the NNS were 2, i.e. 50% of those taking the medicine or other treatment suffered a side effect?

     Fifth, those patients who enrolled in a study group are probably not typical of the average patient, and the results quoted for them may not apply to you. The study group patients are highly motivated,  have a strong interest in staying healthy, and are committed to seeing the doctor when scheduled. Also their reporting of side effects may not encompass all possible side effects if a question about the possible effect is not included on the questionnaire. A case in point is that  a few men who took Viagra reported seeing a bluish tint to their field of view, a reaction that certainly was not looked for until it was first reported.

     Then we have the case of honest error. Many clinical studies are not borne out when they are repeated by another researcher or research group. This is in part due to the fact that with commonly accepted statistical medical analysis there is at least a 5% chance that the beneficial conclusion was reached by error.
Or it may be simply that the second study group differed in some important way from the first. There are many, many cases of the New England Journal of Medicine, or Lancet publishing back-to-back articles which come to opposite conclusions about a seemingly identical clinical treatment of the same medical problem.

     You should also be aware of the placebo effect. Many studies have demonstrated a placebo effect of 30% across the board. In other words, taking a sugar pill or an injection of normal saline can produce a beneficial effect.
This may be related to the fact that almost all patients feel instantly better as soon as the doctor walks into the examination room wearing a white coat. The human brain is a marvelous organ, and the mind-body interaction is always occurring, either on an unconscious or subconscious level. Believing can sometimes make it so, but we don't know how to engender that believing on a consistent basis.

     Finally, distrust all medical advertisements about the wonderfulness of the doctor or clinic or hospital doing the advertising. If they were that wonderful, they would not need to advertise. I especially dislike the ad (hospital name deliberately omitted) "Cancer. Where you're treated first can make all the difference." The insidious suggestion is that if you do not go to them for treatment and your cancer spreads you only have yourself to blame!!!

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