It’s easy to think of medical tests as black and white. If the test is positive, you have the disease; if it’s negative, you don’t. Even good clinicians sometimes fall into that trap. Based on the pre-test probability of the disease, a positive test result only increases the probability by a variable amount. An example: if the probability that a patient has a pulmonary embolus (based on symptoms and physical findings) is 10% and you do a D-dimer test, a positive result raises the probability of PE to 17% and a negative result lowers it to 0.2%.
Even something as simple as a throat culture for strep throat can be misleading. It’s possible to have a positive culture because you happen to be an asymptomatic strep carrier, while your current symptoms of fever and sore throat are actually due to a virus. Not to mention all the things that might have gone wrong in the lab: a mix-up of specimens, contamination, inaccurate recording…
Mammography is widely used to screen for breast cancer. Most patients and even some doctors think that if you have a positive mammogram you almost certainly have breast cancer. Not true. A positive result actually means the patient has about a 10% chance of cancer. 9 out of 10 positives are false positives.
But women don’t just get one mammogram. They get them every year or two. After 3 mammograms, 18% of women will have had a false positive. After ten exams, the rate rises to 49.1%. In a study of 2400 women who had an average of 4 mammograms over a 10 year period, the false positive tests led to 870 outpatient appointments, 539 diagnostic mammograms, 186 ultrasound examinations, 188 biopsies, and 1 hospitalization. There are also concerns about changes in behavior and psychological wellbeing following false positives.
Until recently, no one had looked at the cumulative incidence of false positives from other cancer screening tests. A new study in the Annals of Family Medicine has done just that. (more…)
In May 2008, the article “Why the NIH Trial to Assess Chelation Therapy (TACT) Should Be Abandoned” was published online in the Medscape Journal of Medicine. The authors included two of our own SBM bloggers, Kimball Atwood and Wallace Sampson, along with Elizabeth Woeckner and Robert Baratz. It showed that the existing evidence on treating heart disease with IV chelation did not justify further study, and that the TACT trial was questionable on several ethical points. Their ethical concerns were taken seriously enough that enrollment in the trial was put on hold pending an investigation. It has now been re-opened after a few band-aids were applied to the ethical concerns. The scientific concerns were never addressed.
I have seen many critiques of the Atwood study, and not a single one has offered any cogent criticism of its factual content or reasoning. Most of them could have been written by someone who had not bothered to read beyond the title. Their arguments can be boiled down to a few puerile points that can be further simplified to:
(1) I believe the testimonial evidence that chelation works.
(2) Atwood and his co-authors are bad guys.
Now Beth Clay has chimed in with an article entitled “Study of Chelation Therapy Should Not Be Abandoned.” I found it truly painful to read, but even the worst has some value as a bad example. Clay’s article could be used for a game of “Count the Errors.” I will point out some of them below. (more…)
A new book, Science Under Siege: Defending Science, Exposing Pseudoscience addresses many of the issues near and dear to the hearts of SBM bloggers and readers. A compilation of some of the best writing from the last few years of Skeptical Inquirer magazine, it’s not only good reading but can serve as a useful reference.
Skeptical Inquirer is the official magazine of what was formerly called The Committee for the Skeptical Investigation of Claims of the Paranormal (CSICOP). It was formed in 1976 and in its early days it concentrated on things like Bigfoot, UFOs and psychics. It has morphed into the Committee for Skeptical Inquiry and the magazine is now described on its cover as “The Magazine for Science and Reason.” It has gone way beyond paranormal claims to address everything from intelligent design to AIDS denial. In the 3 decades of its existence it has performed an invaluable service by investigating alleged phenomena and testing claims scientifically, providing natural explanations for weird observations, refuting pseudoscientific arguments, and teaching people how science works and how to think critically.
We now have many skeptical magazines, including Michael Shermer’s Skeptic in the US and similarly named publications in the UK, Australia and elsewhere. But Skeptical Inquirer was the first. It was the trailblazer and set the standard.
The word “skeptic” has negative connotations for some. But it is really a positive, inquisitive, reality-based approach to all aspects of life. A skeptic is a person who asks for evidence before accepting a belief and who asks if there could be another explanation other than the first one that is offered. Scientists are skeptics. Skeptics think scientifically. (more…)
I was recently asked to write about vaccines and autism for Skeptic magazine. I approached the project with trepidation. So much has been written, from Paul Offit’s book Autism’s False Prophets to a veritable flood of blogorrhea on the Internet. I didn’t have anything new to add, and I couldn’t hope to cover all aspects of the subject.
After some thought, I realized I could contribute something useful. I could organize the highlights into a concise and accessible story. While it awaits publication in the magazine, Michael Shermer elected to pre-publish it in the e-Skeptic newsletter. You can read it here.
There is a very good chance that you will feel worse after seeing a chiropractor.
According to a new systematic review, serious complications of spinal manipulation are rare, but 33-60% of patients experience milder short-term adverse effects such as increased pain, radiation of pain, headaches, vertigo and even loss of consciousness. The study, published in the journal Spine, involved searching PubMed and the Cochrane Library for the years 1966 to 2007. They identified additional studies by hand searching. They looked for all articles that reported adverse effects associated with chiropractic irrespective of type of design. They omitted any reports where patients had underlying diseases (osteogenesis imperfecta, expansive vertebral hemangioma, osteoporotic fracture, etc.) that predisposed them to complications with manipulation.
They found 46 pertinent studies:
- One randomized controlled trial
- Two case-control studies
- Six prospective studies
- Twelve surveys
- Three retrospective studies
- 115 case reports
They recognized that “the heterogeneity of the study designs did not allow conducting a formal meta-analysis.” But they did the best they could to make sense out of what they found. (more…)
Last month I wrote about a book on evolutionary medicine that I could not recommend. Now I’ve found one I can recommend. Marlene Zuk, an evolutionary biologist at the University of California, Riverside, has written a delightful book entitled Riddled with Life: Friendly Worms, Ladybug Sex, and the Parasites That Make Us Who We Are. She describes how our parasites and diseases co-evolved with us: as we developed better defenses, they developed better weapons. “We do not choose to have them, but our lives are unimaginable without them, and for better or worse, they have made us who we are.” Parasites have altered our bodies in ways that science fiction filmmakers could never have imagined. She even suggests that we can thank parasites for the fact that we reproduce sexually rather than asexually.
She advocates an evolutionary medicine that “places diseases and defects in an evolutionary framework to make sense of the apparent mismatch between the way our bodies often work and the way we would like them to.” Evolution did not design our bodies for health, but to maximize reproduction.
“Just because our species evolved in a different environment does not mean …that following the ways of the past is automatically going to free us from the illnesses of modern life.” She incisively debunks the myth of the Paleolithic diet and points out that if we wanted to copy our hunter-gatherer ancestors we would have no way of deciding which ones to copy – the ones from 10,000 years ago or the ones from 100,000 years ago; the Inuits or the Kalahari Bushmen. She also points out that evolution explains why humans vary and why one diet won’t suit everyone. (more…)
Alcoholics Anonymous is the most widely used treatment for alcoholism. It is mandated by the courts, accepted by mainstream medicine, and required by insurance companies. AA is generally assumed to be the most effective treatment for alcoholism, or at least “an” effective treatment. That assumption is wrong.
We hear about a few success stories, but not about the many failures. AA’s own statistics show that after 6 months, 93% of new attendees have left the program. The research on AA is handily summarized in a Wikipedia article. A recent Cochrane systematic review found no evidence that AA or other 12 step programs are effective.
In The Skeptic’s Dictionary, Bob Carroll comments:
Neither A.A. nor many other SATs [Substance Abuse Treatments] are based on science, nor do they seem interested in doing any scientific studies which might test whether the treatment they give is effective. (more…)
There is no question that patients on insulin benefit from home monitoring. They need to adjust their insulin dose based on their blood glucose readings to avoid ketoacidosis or insulin shock. But what about patients with non-insulin dependent diabetes, those who are being treated with diet and lifestyle changes or oral medication? Do they benefit from home monitoring? Does it improve their blood glucose levels? Does it make them feel more in control of their disease?
This has been an area of considerable controversy. Various studies have given conflicting results. Those studies have been criticized for various flaws: some were retrospective, non-randomized, not designed to rule out confounding factors, high drop-out rate, subjects already had well-controlled diabetes, etc. A systematic review showed no benefit from monitoring. So a new prospective, randomized, controlled, community based study was designed to help resolve the conflict. (more…)
Three recent news items about chiropractic have particularly irritated me.
(1) U.S. Army Brigadier General Becky Halstead (Retired) Speaks Out for Chiropractic Care
(2) Chiropractic Helps Child with Brain Disorder
(3) Swine Flu Chiropractor’s Handout
(1) General Halstead has become a spokesperson for The Foundation for Chiropractic Progress, a nonprofit organization dedicated to increasing public awareness of chiropractic. Her quoted comments boil down to
- I like the personal attention and caring I get from my chiropractor.
- Chiropractic advice about healthy lifestyle is essential
- Chiropractic care prevents more serious health concerns
- Chiropractic is essential for assisting in recovery from minor injuries.
- Chiropractors don’t mask the problem with drugs and all their side effects.
- Chiropractors are holistic and involve the patient in her own care.
- “Listening appears to be a major tool.”
This is nothing but opinion based on personal experience and scientific ignorance. She offers no evidence that chiropractic theory is true, that chiropractic adjustments are effective, or that a chiropractor has any advantage over a science-based medical doctor who also spends time listening to patients, is interested in the whole patient, advises about healthy lifestyle, and avoids unnecessary use of drugs. Caring clinicians can be found in chiropractic, in homeopathy, in every kind of quackery, and in scientific medicine, with the advantage that the scientific clinician can also provide effective evidence-based treatments. (more…)
I read this Reuters Health article on MedlinePlus, and then I read the study the article referred to (The impact of acupuncture on in vitro fertilization) and now my head hurts. The study found that acupuncture was not effective in increasing the pregnancy rate (PR) during in vitro fertilization (IVF). As quoted on MedlinePlus, the lead author, Alice Domar, seems to blame her patients (the presumably poor quality of their embryos) rather than acupuncture for the lack of success, and then she recommends using acupuncture even if it doesn’t work. That was bad enough, but “poor quality embryos” is a hypothesis that was actually tested and rejected in the study itself. Has Domar forgotten?
The headline of the MedlinePlus article says “acupuncture doesn’t boost IVF success for all” – suggesting that it boosts success for some? Then the first sentence says the study suggested that acupuncture doesn’t work, period. But wait…
The lead researcher says acupuncture may not have worked in her study because, unlike past research, her investigation wasn’t limited to women who had good quality embryos available for transfer. “I’m wondering if my sample was just not a good sample, in that most of the patients in my study were probably not the best-prognosis patients,”
Domar and her team say the most likely explanation for the lack of an acupuncture effect in their study was the fact that they included many women who didn’t have good quality embryos available for transfer. While acupuncture may help a woman become pregnant after the transfer of a healthy embryo, the researcher noted in an interview, it can’t repair an embryo with chromosomal defects or other abnormalities.
Hold the boat!! In the Discussion section of the paper itself, Domar et al point out that previous research has included mostly patients with good quality embryos. They ask if perhaps acupuncture only works for good quality embryos? They test that hypothesis by separately analyzing the subjects in this study who had good quality embryos. There was no increase in PR with acupuncture in this sub-group; the results were the same as for the entire sample. (more…)