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Resolving Conflicts in Findings: Vaccine Promotion is Tricky

Aug. 26, 2015 by | Comments (9)

A few months ago I wrote about the psychology of vaccine denial. In the post I discussed two publications, one of which (Nyhan, et al.) found:

Corrective information reduced misperceptions about the vaccine/autism link but nonetheless decreased intent to vaccinate among parents who had the least favorable attitudes toward vaccines. Moreover, images of children who have MMR and a narrative about a child who had measles actually increased beliefs in serious vaccine side effects.

None of the interventions increased parents’ intent to vaccinate.

Then, a couple of weeks ago, a friend sent me a link to this piece describing research which seems to contradict that finding. The authors (Horne, et al.) concluded that

…highlighting factual information about the dangers of communicable diseases can positively impact people’s attitudes to vaccination.

These two conclusions seem to contradict each other. Which should we believe?

Many times this question comes down to the quality of the research. In this case, I believe these are both fairly well-designed studies. One, however, is more precise than the other in several ways. I believe that precision highlights the complexity of the issue as well as giving us a better idea of the direction that vaccine promotion should take.

Let’s look at the differences in sampling and method between the two studies.

The Horne study sampled 315 men and women. In the Nyhan study, the final sample was 1759 parents with children under the age of 18. In most research, 315 subjects is more than sufficient and more is not always better. The danger in larger samples is to find effects that are statistically significant, but not practically significant. However, when comparing conflicting findings, it is best to bet on the side of the larger sample.

Then there’s the question of limiting the study to parents. Although Horne compared parents to non-parents and found no significant differences in attitudes or effects, noise is noise. These two groups of people vary, and the attitudes of non-parents are not particularly relevant. Limiting the study to parents would give me more confidence in the robustness of the findings and their application in real-world activism.

Still, if both are reasonably well-designed studies by competent researchers, the end results should not contradict each other. So there must be more going on. And there is.

For one thing, this is a great example of how complex social sciences are. We should never make policy decisions based on a single study and this demonstrates why. Replication, especially with variants of measures and materials, is essential to learning the best methods of persuasion.

For another, these studies differ in more than just sampling techniques. The Horne study is much simpler and, in fact, oversimplifies. Nyhan, et al. included three outcome measures, each addressing a specific attitude:

  1. The belief that vaccines cause autism.
  2. Perceived risk of side effects from vaccines.
  3. Intent to vaccinate one’s child/children.

By contrast, the Horne study involved a single measure which combined answers to five specific questions (such as “I intend to vaccinate my child.” and “Doctors would not recommend vaccines if they were unsafe.” to come up with a more vague “vaccine attitudes” scale. Even if the answers to these questions are highly correlated, how interventions affect those answers may be very different. They certainly were in the Nyhan study. And if “effective” is defined as increasing intent to vaccinate, then the Horne study does not answer the question it purports to answer. Personally, I am more interested in intent to vaccinate than I am in any other aspect of “vaccine attitudes”, so the Nyhan study’s findings are much more meaningful to me.

In general, it is best to measure outcomes of interest as specifically as possible, but of course the more outcomes a researcher studies, the larger the sample must be.

Finally, and perhaps the most important difference between these two studies, is the timing of the experimental portion. When measuring the effect of treatments or interventions on attitudes, an experiment should be spaced over time. A researcher will measure the attitude, then wait before applying a treatment and measuring the attitude again. When polled about attitudes, those attitudes are brought to mind. This affects our receptiveness to relevant information in complex ways, ways that vary based on a number of other factors such as the strengths of our attitudes and the way the questions are worded. However, allowing subjects to forget about the initial survey provides a more accurate picture of how people confronted with information in the real world may respond to it.

The Horne experiment was conducted a day after the initial screening while the Nyhan experiment occurred about two weeks after initial screening.

My conclusion? I think the issue is complex, but while Horne’s findings appear easier to understand, Nyhan’s findings are more specific, answer more interesting questions, and can be more easily viewed within the framework of well-established knowledge about human decision-making (e.g., cognitive dissonance).

That, and we need more research if we are to develop effective ways of increasing vaccination rates.

This post also appears at Barbara Drescher’s personal blog, ICBS Everywhere.
  • Horne Z, Powell D, Hummel JE, & Holyoak KJ (2015). Countering antivaccination attitudes. Proceedings of the National Academy of Sciences of the United States of America, 112(33), 10321-4 PMID: 26240325
  • Nyhan B, Reifler J, Richey S, & Freed GL (2014). Effective messages in vaccine promotion: a randomized trial. Pediatrics, 133(4) PMID: 24590751
Barbara Drescher

Barbara Drescher taught quantitative and cognitive psychology, primarily at California State University, Northridge for a decade. Barbara was a National Science Foundation Fellow and a Phi Kappa Phi Scholar. Her research has been recognized with several awards and the findings discussed in Psychology Today. More recently, Barbara developed educational materials for the James Randi Educational Foundation. Read Barbara’s full bio or her other posts on this blog.

9 responses to “Resolving Conflicts in Findings: Vaccine Promotion is Tricky”

  1. B Morse says:

    Just briefly, I would like to second O Lock’s comment. I am a pediatrician and I do believe in the power of vaccines to help prevent disease. However, not all vaccines are indicated for all patients at all times. Not all parents will choose to vaccinate (in most states in the US, parents still are allowed to choose whether to vaccinate their child or not). The way to convince someone of something, especially when that someone is the loving and responsible parent of a healthy newborn, is not to ignore or belittle their concerns and not to lie to them. The way to convince them is to be fully honest and give as much truthful and relevant information as you can. And then, to let them think about it and ask questions. Most pediatricians do not do this. How many discuss the known porcine virus contaminants in rotavirus vaccine and what is known and what is not known about the repercussions of this viral contamination? I think that we need to learn whatever we can about the diseases we are attempting to prevent, the methods we are using to do so, the benefits and harms, when known, and discuss these things with our patients’ parents. There is no honest way to increase vaccine rates without taking these steps.

  2. O Lock says:

    If you read Ms. De Vore’s comment carefully, you will note her observation that each prescribed drug comes with 2 or 3 pages of ‘side effects’. I have heard variations of this for years. Heck, comedians even joke about it. What docs and pharmacists ignore is that many of the side effects are terrifying: “…even death.”

    To be so dismissive of a person’s apprehensions is reprehensible. Her concerns are legitimate to her. We have unfortunately gone too far in presenting every single possible side effect possible, no matter how rare, to the patient with little to no explanations regarding which is important and which is not. How does a person filter the reams of extremely fine print that comes with many of the packaging or in ads?

    Doctors are quick to wave off patients’ worries about a prescribed drug saying it’s perfectly safe with little more than a drug rep’s say so, or a journal’s review of the drug.

    No, I am not an anti vaxer. I saw the effects of Polio, measles and whooping cough. I knew a kid who died from complications of measles. I also knew a kid who was partially paralysed from one of the vaccinations. Recently I and my wife contracted whooping cough from an unvaccinated child. It took us more than three months to totally get over the illness.

    Drug companies have also been known to lie to the public about how safe their drugs are. Push for unapproved use of drugs. And encourage prescribing for longer periods than approved. It’s not unreasonable for people to be skeptical about what the mfg. says about their products.

    The odds are way in favor of getting children vaccinated. But people’s concerns need to be properly addressed as well. With objective and impartial information. From a source they can trust implicitly.

    • Max says:

      Concerns about side effects are legitimate, but the notion that “these childhood diseases that our dear Mother Nature throws at us have a purpose” is silly magical thinking.

      It would be nice to be able to look up the probabilities of side effects. Usually, they’re grouped into common, rare, and very rare categories, but percentages would be better.
      Common side effects may only affect a minority of patients, and they may be worth tolerating. Cancer treatment has a lot of nasty side effects, but it can save the patient’s life.

      Severe side effects like death tend to be very rare. Swimming can cause death in rare cases, but learning to swim in a controlled environment can save your life, sort of like a vaccine against drowning.

      The hardest risk/benefit calculation is for drugs that treat annoying conditions like acne but have rare life-threatening side effects like liver damage.
      But people risk their lives all the time just for fun and recreation. Skiing and tanning can be deadly. Not to mention recreational drugs, including tobacco and alcohol. It amazes me that some people who worry so much about side effects of prescription drugs will take unregulated illegal recreational drugs just for fun.

  3. Dr. Richard August says:

    I am a pediatrician, have been for over 30 years, and until you’ve held an infant dying from pertussis and had to tell the baby’s parents that their child wouldn’t make it through the night, knowing the entire time that the older children in the family weren’t vaccinated, and the dying baby caught the “whooping cough” from her older siblings — well, I guess willful ignorance is bliss. Not all information gleaned from the Internet is equal. Unfortunately most anti vaxers don’t remember a world full of polio or small pox. Not vaccinating your children is irresponsible beyond all rational belief. The conspiracy theories surrounding the side effects of vaccinations do our society a horrible misjustice.

  4. Maggie De Vore says:

    Without getting into scientific mumbo-jumbo I really believe some of these childhood diseases that our dear Mother Nature throws at us have a purpose. I don’t know what it is. I just had to deal with it with my children and get on with life. No one talked about ‘complications’ or pointed out what ‘might’, ‘may’, or ‘could’ happen.

    There were no ‘vaccinations’ then and I believe that the current push through fear and greed for vaccinations is diabolical. Considering other practices for taking drugs and vaccination ingredients/drugs — we have had an outrageous number of ‘side-effects’ for this new and dangerous method of medical treatment.

    Each prescribed drug comes with 2 or 3 pages of ‘side effects’ — . Oh, but don’t worry doctor has a drug for that! And so the merry-go-round of prescriptions grows with doctors, lawyers, pharma and insurance companies.

    If there ever was a ‘product’ by which these so-called ‘respectable’ corporations use — it is us.

    I really do love the Hippocratic oath and believe it should be a mantra for the world — First, do no harm!!! Please??

    • Max says:

      Ah the good ol’ days of smallpox and polio epidemics before the scientific mumbo-jumbo.

    • Randy Grein says:

      Yes, real life is messy, I get it.

      Unlike magic unicorns doctors don’t have risk-free options. A friend’s father just passed. Heart disease could have easily been mitigated with standard surgery but an aneurysm in a major artery made that dangerous. Ironically the aneurysm could have been repaired but for the risk of heart attack. Any way they chose the risk of death was very high.

      Not so with vaccines, where the risk of serious consequences is like winning the lottery – one person in millions. The risk without vaccines? Oh, about 1 in 5, higher some areas with desperate poverty, overcrowding or poor sanitation. Everyone over 70 knows someone who died or almost died of polio, measles, or one of the other ‘eradicated’ diseases. My mother spent 2 weeks in an iron lung from polio as a teen – and she was lucky. No one is left who lived through the Spanish Flu epidemic of 1918, but it killed between 50 and 100 million people – 2% of the world’s population, in a single year, from a single disease.

      Yes, life is messy, we don’t have perfect information, and everything is a risk. And yes, it takes work to figure out the best option, but really, it’s not that hard, look for the better numbers and make your choice. Or you can play ostrich, but if so please move elsewhere so the rest of us don’t get infected.

  5. Max says:

    Vaccine promotion is not skepticism promotion.
    What if it were proven that scare tactics and peer pressure are much more effective than education at getting parents to vaccinate their kids? If your main goal is to increase vaccination rates by any means, then you may adopt those tactics. But that’s the opposite of promoting skeptical thinking, which is supposed to resist propaganda.

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