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How Should We Argue For Vaccination? PDF Print E-mail
Swift
Written by Kyle Hill   

Back in March a study came out, though it was only recently hyped up in the media, which explored an interesting intersection between psychology, vaccination, and the communication of risk. This study by Cornelia Betsch and Katharina Sachse (2012) covered two experiments in which the researchers looked at how the wording of vaccine risk messages affected participants’ perception of the safety of vaccines.

The idea of these experiments was to explore what the researchers call the negativity bias. This bias is a tendency for negative messages to influence our perceptions of risk more than positive ones. This creates a problem for the communication of negating messages—messages that downplay a risk or offer contradictory evidence against a risk. So, relating to information about vaccines, how strongly should we word our pro-vaccine arguments?

As the science behind vaccine safety is sound, there are a few ways to make an argument for it (and to argue against anti-vaccine pseudoscience). The study outlines two different tactics: strong risk negation and weak risk negation. The study offers up the following example of both:

 

The claim that newborns tolerate vaccinations less well than older infants may be negated by the statement “It is absolutely impossible that newborns tolerate vaccinations less well than older infants,” which may be perceived as a strong and confident negation. A weaker risk negation may be expressed by the following statement: “It is extremely rare that newborns tolerate vaccinations less well than older infants.”

 

Participants in the experiments were asked to imagine that they were parents unsure about vaccination and its side effects, and were then presented with a number of common anti-vaccine arguments and their corresponding strong or weak negations (rebuttals). After this, the participants were asked how likely they would be to vaccinate their imaginary child against a fictitious illness. We could imagine this to be exploring how people would respond to the science-based community’s debunking of anti-vaccine myths.

Herein lies the issue: based on the previous literature on risk communication and the negativity bias, the study hypothesized that a strong risk negation would actually create a higher perception of risk than a weaker negation. This is counter-intuitive, as a strong negation leaves no “residual risk” (i.e., no possibility of harm), which should seemingly assure people. This would be akin to saying “It is absolutely impossible that vaccines will harm your baby.” But because of the negativity bias, even a weak negation (which implies a small risk) affects risk perception more than a strong negation (which implies no risk). That is to say, paradoxically, the study in fact found that a stronger negation of risk increased the perceived probability that a vaccine-adverse event (VAE) would affect their (imagined) child.

The study is not clear on why exactly this is the case. Perhaps a complete negation of risk is simply not “real” enough: claiming that a medical intervention is 100% safe is undoubtedly suspicious. As the negativity bias has us giving more weight to negative information, the weak negation simultaneously offers a negative aspect (“some rare side effects may occur”) while explaining vaccination. It may be that these aspects, when taken together, offer a more “real” message that has an emotional response we can focus on. Delinking this in the strong negation case could be the downfall of effective communication. It could also be that the strong negation, which makes no mention of risk, allows a cautious mind to run wild, inserting hyped-up dangers where none exist.

Of course, like any study, this one has its limitations. The sample size was relatively small (n=166), the participants weren’t actually parents, and there may have been confounding variables like effects from the availability heuristic (simply seeing the risk written down may have increased the perceived probability that it happens). But the study certainly offers an interesting and counter-intuitive finding.

There are many more parts to this study, such as exploring other moderating variables like personal involvement, prior attitudes about vaccination, credibility of the message source, and views of alternative vs. conventional medicine. However, the finding about the negativity bias in communication about risk is enough to inform some strategy for those of us who wish to, rightly, extol the safety and necessity of vaccination (and negate the damage done by anti-vaccine proponents).

Adopting a More Rational Stance

The finding of the study discussed above presents a problem: We know vaccines are safe and save lives, but we can’t discuss it in absolutes. As a pro-vaccine proponent myself, I know that I have been guilty of making statements that sound too similar to the “strong negation” case explained above and have seen many skeptics to the same. The unfounded and fear-based arguments of the anti-vaccine movement frequently get me so incensed that I forget the conditional and tentative nature of the science I am trying to promote. Vaccines are not 100% safe. We can only say that adverse reactions (which do happen) are amazingly rare. [Indeed, even if an order of magnitude more children were in some way harmed by vaccines, the cost-benefit analysis would still point to continued vaccination] Though the vast majority of VAE’s are minor, like soreness or redness at the injection site for example, they still occur.

It is odd then that in this case a cognitive bias sides with the stance of science on an issue. According to risk communication experiments like these, adopting a more conditional and scientifically accurate stance on VAE risk is better than flat-out denying any risk (though the percentages are so small that we might be warranted to do so). If a pro-vaccine message owns up to possible side effects, instead of dismissing any with a strong negation, and therefore decreases the perception of risk in comparison, that is the way to go. It may seem like an information campaign no-no to include possibly scary side effects in the message, but our cognition is quirky. In this case, an honest representation of risk happens to work well with those quirks.

This should logically extend to other anti-vaccine tropes like the imagined link between vaccines and autism. Another study would have to be done, but if the negativity bias holds true across cases, it would be better for pro-vaccine advocates to speak in the conditional voice of science. Saying “all of the evidence that we have so far shows no plausible link between vaccines and autism,” would then be better for people’s understanding of risk than saying “it is absolutely impossible that vaccines cause autism” (even though this is nearly the case).

What then does this mean for pro-vaccine discourse? I suppose that it means speaking more like medical professionals and less like pro-vaccine cheerleaders. I am convinced that getting your child vaccinated is one of the most medically important things that you can do for her, but that does not mean I can leap beyond scientific boundaries and into a place of inscrutable certainty. If we start making claims that go beyond what the science says, we become as those who claim thimerosal is a persistent and evil poison. Luckily, we already have the science on our side. Every bit of evidence that we have shows that vaccines are safe, effective, incur a modicum of side effects, do not cause autism, and save millions of lives. We just have to communicate this in a way that acknowledges the real data. Unfortunately, I don’t think this is because people value real data or know the science behind these issues, but rather it is because, in comparison to statements that leave no wiggle room, weak negations leave room for judgment and suffer less from possible backfire effects.

As does the psychology of “debunking,” the study of risk communication extends to everything from vaccines and autism to cell phones and brain cancer to “alternative medicine.” Studies like the one discussed above are by no means definitive, but they do give us a window into how to proceed as properly science-based individuals. Apparently, when it comes to communicating effectively about vaccination, and debunking the harmful tropes of the anti-vaccine movement, we need to stick to the science, admit the risks when they are present, and stay away from absolutes. Though it is incredibly hard not to adamantly shout back at those who are basically welcoming preventable childhood diseases with open arms, nothing in science is absolute, and we should represent that in the way we promote vaccine safety. A quirky psychology may just be our ticket to scientific literacy on the issue.

 

Journal Source:

Betsch, Cornelia, and Katharina Sachse. “Debunking Vaccination Myths: Strong Risk Negations Can Increase Perceived Vaccination Risks.” Health Psychology, March 2012.

Kyle Hill is the JREF research fellow specializing in communication research and human information processing. He writes daily at the Science-Based Life blog and you can follow him on Twitter here.

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written by jayrayspicer, May 24, 2012
Wouldn't it be simplest and most accurate to speak in terms of relative risk? Something like, "Your unvaccinated child is far more likely to be harmed by pertussis than by the pertussis vaccine." Scientifically accurate, yet a very strong statement. Better yet would be a comparison of actually probabilities, such as, "Your unvaccinated child has a 1% chance of contracting (or spreading) pertussis, whereas a harmful reaction to the vaccine is only seen in 0.0001% of cases." (Substituting the actual percentages, of course.) Better still perhaps, "Any intervention involves some risk, but your unvaccinated child is 1,500 times more likely to be harmed by pertussis than by the pertussis vaccine." (Again, substituting actual research-based numbers.)
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written by Otara, May 24, 2012
I would think most people arent so much worried about quantifiable risks as they are about 'what if you're wrong' risks. Ie thalidomide and the like, where unforeseen effects were identified down the track.

Which is why they use heuristics like the above to decide how trustworthy the information supplier is. A person saying 'there is no risk at all' will never be believable, because the possibility of unknown risks can never be entirely removed.

I tend to agree with jayrayspicer that the real problem is often the understatement of known risks if the vaccine or whatever is not used. Not sure how that would work with things like mobile phones though, ie where the health benefit is fairly low compared to the claimed risks some people are promoting.
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written by jayrayspicer, May 24, 2012
Otara, that's an interesting point about evaluating cell phone risks relative to other things. I suppose we could compare cell phone risks to those from solar radiation, or the far more powerful RF we are exposed to from TV and FM radio stations. It's not as direct a comparison as vaccine vs illness, though.
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Anti-vaxxers' agenda
written by garyg, May 25, 2012
Consider the possibility, too, that those who oppose vaccination may be doing so because they are enamored of a branch of alternative medicine that discourages, or even opposes, vaccination as "unnatural" (naturopaths, and some chiropractors).
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written by kenhamer, May 25, 2012
While not directly related, here's a great way to present statistics that is understandable by everyone. It shows the pros and cons of PSA (prostate cancer) screening, which have recently been recommended *against*.

http://www.harding-center.com/images/stories/artikel_und_pressemeldungen/fact_boxes/factbox_psa_icon_engl.png


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Graphical representation
written by jayrayspicer, May 25, 2012
Kenhamer, that's a great link, but I actually found it easier to understand the numbers in the table form. The chart was actually hard to read, with the embedded characters over some of the circles. But it's a compelling demonstration that prostate screening is not just useless, but harmful. They should have included a number for complications (such as infections) arising from the unnecessary interventions, to really drive the point home.
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Harding Center for Risk Literacy
written by jayrayspicer, May 25, 2012
BTW, the Harding Center for Risk Literacy looks like it could be a very useful resource. I'd never heard of it before.
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written by MadScientist, May 25, 2012
Would you like your child to suffer and die of pertussis? Be pockmarked or even blinded by Chicken Pox? Contract the deadly Hepatitis B? Die of diarrhea brought about by the Rotavirus? If you would wish such a future on your children, then simply don't vaccinate.
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written by Willy K, May 25, 2012
@jayrayspicer You said...
prostate screening is not just useless, but harmful
Screening is harmless, your next sentence states where the actual harm comes from.
complications (such as infections) arising from the unnecessary interventions
One wouldn't say putting a half a liter of water into your body is harmful, except if it's put into your lungs. smilies/cry.gif
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written by jayrayspicer, May 25, 2012
Willy K, screening *is* harmful if it leads to harm. It may not be the proximate cause, but it is still the initial cause. As the link so clearly shows, people who get screenings end up being harmed, unlike people who don't.
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written by Willy K, May 25, 2012
jayrayspicer,

So by your "logic" eating must be harmful, if one eats poison. Walking is harmful, if one walks off a cliff. Breathing is harmful, if one breathes water. I'm sorry old buddy, old pal, I find your chain of logic to be seriously flawed. smilies/wink.gif

Having a few milliliters of blood removed from your body will do you little to no harm. There are some tests that do carry great risk such as an angiogram, but I personally know someone who's alive today because all other less invasive tests did not reveal his blocked cardiac artery! So the benefit for him outweighed the risk.

I'm not arguing for mass PSA screening, the newest science and statistics demonstrate that high PSA numbers are not good predictors of cancer mortality and as you say "unnecessary interventions" are a very good reason to not use widespread screening.

I had a PSA test, I was not harmed, my wallet did suffer a bit, those tests are not cheap!

Nighty night Jay Ray. smilies/smiley.gif
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written by jayrayspicer, May 25, 2012
Willy K, it's a little difficult to believe you are actually this obtuse. An action that one would not otherwise take that in fact leads to harm is harmful, by definition, even though it may well not lead to harm most of the time. Prostate cancer screenings provide no benefit according to the best statistics available, thus they should not be performed, and thus if any harm arises from performing them, the screenings are to blame for the harm.

Your analogies are all inapt, because they all conflate harmful results with otherwise unrelated activities. The only way for a prostate cancer screening to harm you is to have one performed. Eating must be done, but ingesting poison is not necessary. One need not walk off a cliff, though walking is required in order to do so. Breathing may be freely engaged in for decades without breathing water. One need never get screened for prostate cancer, and thus one may completely avoid the possibility of being harmed as an indirect result of prostate cancer screening. A medical test that provides no benefit and occasionally leads to harm should be abandoned on a simple cost/benefit basis. Breathing, walking, and eating all carry distinct risks, but generally the benefits outweigh those risks by a vast margin.

It really is alarming how easy it is to get into a pissing match on the intertubez with even the most uncontroversial comments. Troll much, Willy?
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Thank you
written by baymemnun, May 26, 2012
Thank you useful information ... http://www.yapi-mantolama.com
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written by Willy K, May 26, 2012
Your analogies are all inapt, because they all conflate harmful results with otherwise unrelated activities
My analogies were meant to demonstrate the conflation of your statements.
It really is alarming how easy it is to get into a pissing match on the intertubez with even the most uncontroversial comments. Troll much, Willy?
And with this comment, you now have zero credibility in discussing different points of view. That too bad, you seem to be to be intelligent, but seem to leave no room for deviation from your point of view. smilies/cry.gif
Please go back to Your Vancouver Skeptics and The Huffington Post to make your comments, your Internet trail is easy to find.
https://www.elance.com/s/jayrayspicer/resume/
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written by jayrayspicer, May 26, 2012
Clever sleuthing there, Willy K, considering I haven't been trying to hide. And of course, you miss the point entirely. The data at the link provided by kenhamer clearly demonstrate the harm of prostate cancer screening. Your inapt analogies conflate things that are not necessarily related. It's possible to completely avoid harm from prostate cancer screening by simply avoiding prostate cancer screening. You speak of cost/benefit analysis, yet you don't seem to understand it when it's presented to you. And let's be real clear, Will K, I'm not the one who started with the snark. So who is it it that has credibility problems discussing alternate viewpoints. Maybe if you hadn't hit me with such obvious 'tude, we could have had a pleasant conversation.
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written by Willy K, May 26, 2012
Maybe if you hadn't hit me with such obvious 'tude, we could have had a pleasant conversation.
Well, it may not be sublimely pleasant, but at least it's lively!smilies/grin.gif

So tell me something, do your Vancouver Skeptics meetings ever get this lively? I've wondered about joining skeptics groups in my neck of the woods. Are they more than just drinking and burning effigies of Sylvia Browne? smilies/wink.gif

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written by jayrayspicer, May 26, 2012
No, that's all that happens at skeptics' meetups, Willy K: drinking and burning effigies of Sylvia Browne. You'd probably be bored. You and your 'tude should just stay home and annoy people on the internet with pointless and incorrect pedantry.

If you are actually interested in a different (and more complete) point of view, you might want to look into the difference between proximate and ultimate causes: http://en.wikipedia.org/wiki/P...causation. It is simply incorrect to say that ultimate causes are not causes because a proximate cause intervenes.

In short, and the reason I suspected you of trolling, it is very hard to believe that you actually believe that the harms resulting from prostate cancer screening are somehow unrelated to prostate cancer screening. You do believe in cause and effect, right? Because your comments so far suggest that you're not clear on the idea. If you never get screened for prostate cancer, it's not possible to die from an infection acquired during a biopsy to confirm a false positive prostate cancer screening result. Get it? Or is my logic still faulty? Feel free to point out where I've gone off the rails, and not with fallacious analogies.

And if you want to get really pedantic, every blood draw is harmful, as it requires the destruction of body tissues with a sharp piece of steel. The question is always whether the benefits of a blood draw outweigh the very, very tiny (and easily repaired) harm of a needle prick. If there are no demonstrable benefits, then no blood draw should be performed. That's how cost/benefit analysis works, not by denying that there are costs in the first place simply because they are very, very tiny. The chart at the link above shows clearly that there is no benefit to prostate cancer screening, only harm. Now have we talked this to death, or do you really want to win the internetz that badly?
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To try and steer this pissing contest back on course...
written by Brookston John, May 27, 2012
I think the pro-Vax message should in no uncertain terms inform people who refuse to vaccinate their kids because of what some plastic-breasted "celebrity" says that they are committing child abuse on their children by not vaccinating their kids against easily-preventable diseases.
Chicken Pox "parties" and message boards where you can have people send you their sick kid's clothes so your kid can get sick and develop "natural" immunity? What's next? Public stoning of Homosexuals?

And I like the DRE. My doctor's cute, and I'm kinky (yeah, I know, it's only kinky if she uses her fist). Would you people who are against the PSA test be cool with them implanting a grenade with a random time fuse up your ass? I ask because that's how I think about my prostate, it's a ticking time bomb, and one of these days it'll blow up and kill me..
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written by Willy K, May 27, 2012
Jay,
Your first comment on this posting was was excellent, what happened?

You now seem to be projecting your hostility onto me. I tried to lighten the mood by asking you about the skeptic group you are a member of, I used several positive emoticons to demonstrate that my questions were conversational and not confrontational but you persist in making negatives comments about me.

The title of this post is "How Should We Argue For Vaccination?" not "How Can We Dismiss Willy K's Comments With As Many Insults As Possible?" smilies/cry.gif

My main goal in commenting on Randi's' JREF Swift Blog is to find rational ways to engage with the believers of woo without making them feel as if they are be attacked.
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written by Willy K, May 27, 2012
EDIT: "...without making them feel as if they are be attacked"
should read
"...without making them feel as if they are being attacked."

Dang these old eyeballs in my head!
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written by jayrayspicer, May 27, 2012
Sorry Willy K, but emoticons don't cut it. Your comments were and are snarky. Your tone is unpleasant, and emoticons don't fix that. I'm surprised nobody has pointed this out to you before. What you say is more important than how you decorate.

What happened here is that you attacked me first when you said, "So by your 'logic' eating must be harmful, if one eats poison. Walking is harmful, if one walks off a cliff. Breathing is harmful, if one breathes water. I'm sorry old buddy, old pal, I find your chain of logic to be seriously flawed." You followed that with a winky emoticon that in no way negated your (flawed) assault on my intelligence. And then you signed off with a condescending and dismissive, "Nighty night Jay Ray."

Those are the words of a dismissive, holier-than-thou jerk, Willy K, emoticons be damned. If you want to have grownup conversations with people, start by speaking and disagreeing like a grownup. But apparently you prefer to have "lively" conversations. If you look thru the thread, my comments were respectful until you dragged the tone down (again, highly suggestive of trolling).

As if that weren't enough, you included a post with my photo and breadcrumbs, which I have to say strikes me as stalkerish and not a little threatening. Not to mention juvenile and petty.

In short, if you want to avoid the appearance of attacking people, Willy K, you should probably work a little harder at that. And if you want to talk about logic, you need to learn more about it, or at least not dismiss people who are respectfully attempting to educate you. I don't take kindly to insults, even if you try to pretend they're not insults by tacking on emoticons. I don't know you at all, so if you are simply teasing, how in the world am I supposed to know? It just looked like bullying to me.

And Brookston John, you're welcome to have the DRE if you want it. I find it uncomfortable and degrading, but to each his own. As to comparing your prostate to a hand-grenade on a random timer, you are definitely overstating the risk, as the link above so clearly shows. Do you have similar feelings about your heart, which could give out at any minute, or your brain, which could suffer from a stroke? The risks of those things are much, much greater than the risk of prostate cancer killing you. You are more likely to drown, actually. See http://en.wikipedia.org/wiki/L...ted_States
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written by Willy K, May 27, 2012
Jay, from your latest comment.
...you attacked me... ...attacking people... ...condescending and dismissive... ...assault on my intelligence... ...I don't take kindly to insults... ...looked like bullying to me...

Wow, you are seriously paranoid.
You keep trying to bait me. This will be my last response to you. smilies/cry.gif
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written by jayrayspicer, May 27, 2012
Right, Willy K, you hammer me repeatedly with condescension, sarcasm, and stalking behavior (I'm still tempted to report that one as an abusive post), and I'm paranoid?

You say, "My main goal in commenting on Randi's' JREF Swift Blog is to find rational ways to engage with the believers of woo without making them feel as if they are be attacked." If you are sincere in this goal, then you need to take an honest look at the things you wrote to me and understand how they are likely to be perceived. If you want to engage with people without making them feel as if they are being attacked, then you would do well to a) keep a civil tongue in your head and abandon the ludicrous idea that emoticons can repair the damage being done with your words, and b) take it to heart when somebody objects to your tone, especially when you started it. If you do not do these things, then I would very much like to not ever hear from you again.
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