There is a chance that anti-vaccine types are right

This is a short post. I promise.

“Promise.”

My training as an epidemiologist included biostatistics, and a lot of them. As one of my readers has pointed out, biostatistics is a bit of a dark art. You really need to be comfortable with it to get through it. Like a friend of ours is doing now, I had a bit of a rough time getting through statistics in college and biostatistics for my master’s degree. Epidemiologists use biostatistics to make sure, beyond a reasonable doubt, that the observations and associations you are making are not happening by chance.

People who deny things that don’t happen by chance and embrace things that do are a drag on us all. Of course, I’m talking about anti-vaccine activists. Who else?

Yet, statistics and physics dictates that there is a chance that anti-vaccine types are right, and that the rest of us who look at rational and reasonable explanations for the associations between vaccines and a host of diseases and conditions are wrong. However, it is a small chance. How small? Well, have you ever heard of the infinite monkey theorem?

The theorem states that the universe is so vast and infinite (or that time is infinite) that a monkey randomly hitting the keys of a typewriter will surely, eventually, write the complete works of Shakespeare. Coming up to this conclusion requires some math and some imagination, a bit of a thought experiment, if you will. Just imagine the monkey typing away furiously, forever. It will type out all of the words in the English language, then it will type them in order, and then that order will eventually be the works of Shakespeare.

The same can be said of anti-vaccine activists and their blogs and pamphlets, their meetings in the Cayman Islands and their books about “the truth”, and their accusations aimed at anyone who has even a small hint of an association with anyone who has a thread of a connection to anyone who lives in the vicinity of anyone who works for a pharmaceutical company and dares to vaccinate. They’re bound to get a fact right here and there, as long as they keep at it.

And, trust me, they’ll keep at it.

Child mortality rates by the numbers

Another one of the things that anti-vaccine and alternative medicine (which is not medicine, by the way) use to justify their corrupted way of thinking is the fact that the United States is not at the bottom of the list when it comes to infant mortality rates. If you look at the headlines, the US has the highest infant mortality rate in the industrialized world. Maybe. To the anti-vaccine activists, it’s because the US has a robust vaccination program. To the alt med crowd, it’s because we rely so heavily on medicine to, you know, get cured from disease. I’m almost willing to bet that it’s because we drive too many cars to the environmental activists and because we have too many Mexicans to the anti-immigration bigots. That’s how bias works. You see something and attribute it to the thing you hate.

But why did I write “maybe” up there?

Let’s play Russian Roulette

One of the things that amazes me the most about anti-vaccine (and anti-science) people is their lack of perception when it comes to risk. One in a million chance of Guillain-Barre Syndrome from the flu vaccine? UNACCEPTABLE! One in one-thousand chance of encephalitis from measles? YEAH, I CAN LIVE WITH THAT. It makes me think that they would be really bad at playing Russian Roulette, and here’s why.
Russian Roulette is a dangerous game, and I do not want anyone playing it. Got it?

However, if you were to play it, here’s how it would go:

1. A six-chambered revolver is loaded with one bullet.
2. The barrel is spun by the player.
3. The barrel is locked.
4. The gun is pointed to the player’s head.
5. The trigger is pulled.
6. Hilarity ensues.

All things being equal, your chance of plastering your brains all over the wall and other players is one in six. One bullet, six chambers, get it? So what would you do if presented with one gun with twelve chambers and one gun with six chambers, which one would you like to play with? I don’t know about you, but I’d play with the twelve-chambered one.

If the flu vaccine is as horrible as some would put it, it is at worst a one million-chambered gun with one bullet in one of those chambers. You spin the barrel, pull the trigger, and then pass it on. If you don’t blow your brains off, you then have a 60-70% chance of being protected against the flu. No, you don’t get 100% protection. The man-made flu vaccine is not 100% effective. Nothing is.

We’re not gods.

But anti-vaccine activists will tell you that your chance of dying — yes, dying — from the flu vaccine are high. They won’t quote you the number so as to not reveal their ruse, but they will tell you that it’s horrible. I just don’t get it. Do they really think we’re all idiots?

Don’t get an anti-vaxer to be your partner in a gunfight.

When statistically significant is insignificant

I love Twitter. I got a hold of this little bit of anti-vax nonsense and just had to bring it to everyone’s attention. Check this out:

Source.

You can click on the image to see it a little larger. The original caption is what caught my eye. It reads: “Snapshot of the Verstraeten study dated 02/29/00 showing a statistically significant relationship between mercury exposure and autism.” My emphasis added in bold because this image shows no such thing. It shows a statistically insignificant relationship between mercury exposure and autism.

However, I realize that some of these terms might as well be in Chinese to some of you, unless you speak Chinese. So let’s break it down piece by piece.

Relative Risk (RR) is the ratio in the risk of developing autism given an exposure to thimerosal between a control and an intervention group. That’s the left-hand axis. The control group doesn’t get thimerosal. The intervention group does.

For example, if the RR is 10, then those exposed to thimerosal have a ten times higher risk of developing autism than those who were not exposed. An RR of 1 means that there is no difference in the risks; both exposed and unexposed have equal risks of developing autism. So, an RR of 1 means that the relationship observed is not statistically significant.

Statistical significance means that the results you observe are not due to random chance. That’s the 95% confidence interval (CI) part. That CI tells you the range of RR values you’d see 95 out of 100 times if you repeated the same experiment 100 times. The CI in this chart is represented by the error bars in each value.

At <37.5 micrograms, there was no difference between the two groups. The RR was 1. Note the lack of error bars for that value because of the low number of study subjects (n=5).

At 37.5 micrograms, the RR is still 1. Again, no difference.

At 50 micrograms, the RR is 0.93. This means that the control group is about 7% more likely to develop autism than the thimerosal group. BUT the CI includes 1, so there is a very good chance that your RR will be 1 if you repeat the experiment 100 times. As a result, this finding is not statistically significance. Certainly, I would not go out to the streets and proclaim that thimerosal protects from autism.

At 62.5 micrograms, the RR is 1.26, meaning that the group receiving thimerosal is 26% more likely to get autism than the control group. BUT look at the CI again! It still includes 1. As before, this result is statistically insignificant.

At over 62.5 micrograms, the RR rises to 2.48. The CI still includes 1. This result is statistically insignificant.

Wait! Doesn’t this show a trend whereby if the exposure is high enough, then the association will be stronger? Nope. It doesn’t. If you look at the error bars, you could hit 1.0 the whole time. Heck, with the logic shown in this article, I could make a case that thimerosal is protective against autism at certain levels.

It’s nonsense (to not use a harsher word).

But anti-vaccine advocates are not known for letting facts get in the way. The author of that piece of nonsense continues with quotes taken out of context from some meeting long used by anti-vaxers as evidence of a plot… Blah! Blah! Blah!

If you don’t know what is statistically significant and what is not, then that pretty much destroys your entire argument from the get-go. If you try to come off as a researcher, when you’re obviously not, then you lose the argument even worse.

But what about that study? Well, read all about it here, here, here, and here, and see how it has been misused to further the anti-vaccine agenda. Too bad they don’t know the difference between significant and insignificant, or they would have not used this study (or this graph).

Let’s play with numbers, and your head, just a little bit

From this site:

“New research brought to us by The Lancet shows some startling news regarding the true effectiveness of the flu vaccination. The study involved a control group of 13,095 adults who were not vaccinated. The group were watched to see if they caught the influenza virus, but 97 percent of them did not. Only 2.7 percent, or 357 people, of the non-vaccinated group ended up catching the virus. Another group of adults whom were vaccinated with a trivalent inactivated influenza vaccine ended up with 1.2 percent of them not catching the flu. The difference between the two outcomes is 1.5 people out of 100 which shows that the flu vaccine only prevents the flu in 1.5 out of every 100 adults injected with the flu vaccine.”
 
Emphasis so totally not mine.

But the person then explains their own misunderstanding:

“While the media runs around “spreading the rumor” that flu shots are 60 percent effective, one would assume that 60 out of 100 people receive the flu based on those claims. The problem with this claim is that it’s wrong. Anyone who takes a crash course in college statistics knows how to skew data. Methods for exaggerating data range from manipulating the graph to using complex statistical algorithms to eventually reach the desired conclusion. In this case, the 60 percent effectiveness claim births from an ongoing equation which transforms the numbers properly. First, 2.73% is taken for the people who got the flu in the control group. That number is then divided into 1.18% which stands for the percentage of people who got the flu in the treatment group. The answer comes out  to be 0.43. You are now able to say that 0.43 is 43% of 2.73 (control group people who got the flu) and make the claim 57% are protected by the flu vaccine.”

Well, yes, that’s how it works. This is what we epidemiologists call a “case-control” study, and it is very robust in terms of determining whether or not things happen by chance. In short, that reduction in influenza was not by chance, and it was significant, and it was by more than a half. But let me explain it differently.

The problem with looking at things in terms of percentages is that you lose sight of the magnitude of what you are looking at. If I tell you that 1% of the population of the United States has an ailment, you might think that’s not worth it to try and find a cure or prevention for it. But that 1% translates into roughly 3 million people. That’s a large city!

In the study cited by this particular anti-vaxer, you had a reduction in cases from 2.73% to 1.18%. Using our example of the US population, this would translate into helping 4.65 million people avoid the flu. In this person’s mind, going from 8.19 million to 4.65 million is meaningless. This person seems to be playing mind games to try and convince you that this is not a significant finding. It is, very much. It just seems small because, again, you’re looking at percentages.

So don’t just look at the percentages. Look a the whole picture. Even a reduction in disease burden of 1% or 2% is huge when it comes to saving lives and maintaining productivity.

Related articles elsewhere online (via Zemanta):

• Universal flu vaccine?
• The Flu: A Guide For Parents
• Canada researchers find clues to a universal flu vaccine
• More Than 690,000 Americans Have Already Been Vaccinated Against The Flu This Season, SDI Reports – Cdc Supports Expanded Access To Flu Vaccination
• Flu Shots and Flu Vaccines: It’s Not Too Late