Just in time for Halloween:
I came across this 2-minute video by Brian Zikmund-Fisher, a professor of Health Behavior and Health Education at the University of Michigan, and I took a look because I was curious what he had to say. The video is called “Why aren’t we more scared of measles?” and has the following description:
Measles is one of the leading causes of death amongst children worldwide. In 2012, an estimated 122,000 people died of the disease according to the World Health Organization – equivalent to 14 deaths every hour. Yet talk to parents about this highly infectious disease, and the response is often a resounding “meh”. Why is this?
My first thought was most of the estimated 122,000 deaths are occurring in other countries but he’s looking at attitudes in the U.S., so it’s not clear how relevant this global figure is. So what are the numbers here? I did a quick google and found that there has been a sharp increase in measles in the U.S. this year (“A total of 288 confirmed measles cases” from Jan-May 2014, compared to 220 cases reported in all of 2011), of which half were in children, and zero deaths.
Or, as it might be put in the above blurb, this is equivalent to 0 deaths every hour!
So people’s attitudes on measles don’t seem so mysterious to me. There’s this disease that’s killing people in other countries but not in the U.S., and Americans aren’t worried about it. There have been some scattered outbreaks recently, and public health officials are rightly concerned, but it hasn’t hit the radar of most people in this country.
At this point I was wondering what the video was going to say. The online description continues:
It’s a fantastic introduction to why seemingly rational people sometimes behave the way they do toward vaccines.
According to Zikmund-Fisher, how we think about infectious diseases and risk is governed in part by the way our memories and feelings inform our perceptions – this is referred to by psychologists as the “availability heuristic”. It turns out that when we try and figure out how rare or common a disease is, we try to think of people we have heard of who have had it. If we know of people, we’re pre-programmed to feel more at risk than if we don’t. And surprisingly, the statistics – the actual numbers of people who get sick – don’t seem to matter.
Then I watched the video, and indeed the above paragraph pretty much describes what he said there. And it makes no sense to me.
We aren’t so scared of measles here because it’s not killing Americans and it hasn’t done so for decades. Now Zikmund-Fisher is saying we should be scared. Fair enough: there’s a risk if you don’t get the vaccine because then you can catch it some other non-vaccinated person, maybe from some other country where vaccination rates are low. All this makes sense but I don’t see the availability heuristic being the problem. People are actually making reasonable statistical inferences—no Americans are dying of measles and very few people are getting sick of it, so indeed it is appropriate for them to require additional information (in this case, CDC alerts spread by the news media) before changing their attitudes.
Here’s the point. Based on the information available to me, I agree with Zikmund-Fisher that everyone should get the measles vaccine. This decision makes sense based on the costs, risks, and benefits of vaccination. But I don’t see that availability bias comes in here. Part of the assessment of benefits is the existing rate of measles—and people are doing a pretty good job if they estimate this as near-zero.
Again, look at this from Zikmund-Fisher:
When we try and figure out how rare or common a disease is, we try to think of people we have heard of who have had it. If we know of people, we’re pre-programmed to feel more at risk than if we don’t. And surprisingly, the statistics – the actual numbers of people who get sick – don’t seem to matter.
But people are correctly estimating how rare or common the disease is here: almost nobody in the United States gets measles and nobody dies from it. Those risks might change, but to hold this view requires additional information, not just “the statistics – the actual numbers of people who get sick.”
What the health experts are saying—and it is completely reasonable—is that, in assessing the risks, people should not simply make a decision based on the actual numbers of people who get sick, but instead to look at look at new risks that have barely appeared here. That’s fine but it doesn’t have much to do with availability bias.
P.S. What’s really weird to me is that an expert in risk communication would summarize the risk as “14 deaths every hour”! Of all ways of summarizing, this just seems like one of the more confusing. I mean, why didn’t he go whole hog and give it a description such as, “If each measles death were a 10-pound bag of gold, it would be costing us 20 billion dollars a year.” Or a classic such as, “If you were to lay the measles victims end to end, they’d stretch all the way from Pittsburgh to Youngstown, and almost all the way back!”