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Archive for June 30th, 2009

I get mail–chiroquacktic edition

A long while back, at the original wordpress incarnation of my usual blog, I wrote a piece on the reasons that chiropractic is unscientific nonsense. Because it was popular, I resurrected it. Well, a chiropractor has come to bravely defend his field and left me a comment.

A study in the May 2007 issue of the Journal of Manipulative and Physiological Therapeutics reports health plans that use Chiropractors as Primary Care Providers (PCPs) reduce their health care utilization costs significantly.

The study covers the seven-year period from 1999 to 2005. Researchers compared costs and utilization data from an Independent Physicians Association (IPA) that uses Chiropractors as PCPs and a traditional HMO that doesn’t.

The Chiropractic PCPs had 59 percent fewer hospitalizations, 62 percent fewer outpatient surgical cases and 85 percent lower drug costs compared with the HMO plans.

The patients in the Chiropractic PCP group also reported higher satisfaction with their care than the HMO group. Over the seven-year period, Chiropractic patients consistently demonstrated a high degree of satisfaction with their care that ranged from 89 percent to 100 percent.

Study co-author James Winterstein, D.C. says that patients using Chiropractic PCP health care groups “experienced fewer hospitalizations, underwent fewer surgeries and used considerably fewer pharmaceuticals than HMO patients who received traditional medical care.”

Hmmm…interesting assertions. Let’s examine these assertions and the “article” they come from. (more…)

Posted in: Science and Medicine

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Screening Tests – Cumulative Incidence of False Positives

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…)

Posted in: Clinical Trials

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