Doctor House, Please Meet Mister Bayes

Let’s assume there’s some deadly disease out there, but there’s a pretty good test for it which is 90% accurate (if a person is sick – the test will claim he’s sick in 90% of the cases, and if a person is healthy – the test will claim he’s healthy in 90% of the cases). Now, assuming you took this 90% accurate test, and got a positive result implying you are sick - what are the odds that you are really sick?

Think of your answer before proceeding.

Most of you are probably thinking about 90%, and obviously, that's wrong (otherwise this post would be pointless). I intentionally left out a crucial piece of data which is that this disease affects 1 in every 10 people. Like many problems such as this, it looks very simple, but since most people never heard of Bayes’ theorem, they will only consider the test’s accuracy, ignoring the prior likelihood of the disease. I could use the formula, but I think using an example is much simpler. Let’s say 100 people take this test. Since the disease affects 10% of the population, 10 are really sick. The accuracy of the test is 90%, so 9 of them will get a positive result (true positives). From the other 90 people which are healthy, 81 will get a correct negative result, but 9 will get a positive result although they’re actually healthy (false positives). So after testing 100 people you end up with 18 people with positive results, but only 9 of them are true positives. 9/18=0.5=50%, so, the final answer is: Assuming you took this 90% accurate test to a disease that affects 10% of the population, and got a positive result implying you are sick – the actual odds that you are really sick are only 50%. Several studies where similar problems were presented to real doctors, demonstrated that only about 15% of them get it right. Isn't that amazing? 85% of the doctors will tell you you've got a pessimistic 90% chance of dying really soon, when actually there's a semi-optimistic 50% chance that there's nothing wrong with you! Now that you know this, will you ever be able to trust your doctor again when probabilities are involved?

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p.s. I think, therefore I am wrong.

Welcome to Placebo Land - Alternative Medicine

Although science is constantly expanding our understanding of the human body, alternative medicine is on the rise, sneaking in through the conventional medicine’s back door, disguising itself as “complementary” medicine. I admit western medicine is still very young and has a long way to go, but falling back to unproven old eastern techniques is just loco.

To set things straight, I think that herbal medicine can sometimes work (after all, many conventional drugs are based on plants, although I think modern western drugs will often be more effective), and I believe acupuncture can sometimes reduce pain (by physically touching nerves), but that’s about it.

I don’t think healing hands of light can cure cancer. I don’t believe you can treat a person’s kidneys or liver by applying pressure on his feet. I don’t think you can diagnose a disease by looking at a man’s iris or his aura. And no, if you excessively dilute a drug in water - you get just water. I don’t believe in therapeutic aromatic oils. No stones of power. No crystals of energy. No meridians. No chakras. No ch’i. Just one expensive placebo-based fake medicine.

Don’t get me wrong, I do believe the placebo effect can help a little bit in certain situations like depression or pain, but when people are mistakenly choosing this kind of treatment over mainstream medicine when seeking help for serious problems - that is dangerous.

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p.s. Can the Flying Spaghetti Monster create a meatball too heavy for it to lift?