Blog Archive

Tuesday, March 25, 2014

Vaccinations and Data Viz: A Case Study (Part 3 of 3)

In the third and final part of our case study (see Parts 1 and Parts 2 if you haven't previously read them) we attempted to develop an alternative data visualization to a bubble chart data visualization of the outbreaks of vaccine-preventable diseases (VPDs) world-wide. In those original first and second parts, we evaluated the visual effectiveness of the bubble chart, the provenance of the data, and whether the context was appropriate. As we explained, we felt that there might be better visual options for this story. 

Again, here's the visual, and the link to the original L.A. Times blog

As we developed our own alternative visuals, we came to our most important conclusion: the story was probably miscast. The story is neither a global or a national story. It's in fact a local story. And it’s not about history or trends. It’s about risk. Local communities have high local risk. Local communities can effect local action to protect themselves against outbreaks, and the importance of being community minded about how we increase and maintain immunity.

Through this series, we found a few things:
  • We cannot generalize the state of vaccine-preventable diseases (VPDs) - globally, or even nation-wide. There are some areas that have been unaffected; others, substantially. 
  • And, in fact, taken as a whole nationally, despite the "anti-vaccination movement," as it has been dubbed, the immunization rates haven't significantly changed. 
  • But locally, we are having significant and scary breakouts. This highlights the importance of looking the parts as well as the sum. Vulnerability is highly varied by community and by context. We have clusters of high risk in what seems to be a low risk population.
So, in this final blog post, we talk about some alternative visualizations that might better convey the story, which is about local vulnerability and risk. But first, to explain each of the points above with some examples: 

1. We cannot generalize as a whole the state of VPDs. Here's an exciting visual that we created that depicts the recent trend in pertussis cases, aka whooping cough, that might be as visually compelling as the original bubble chart. In this case, instead of a geographic bubble chart, we wanted to show a historic trend line. The result: a compelling message that surprised us. Have we really regressed to the 1950's? And we wondered, what if other things, like technology, regressed in our country to that of the 1950's. Would we accept that? Of course not! 

But not all VPDs have this same trend. Here's an alternative, seemingly positive outcome for measles. 

However, in the face of this assertion, we are also simultaneously experiencing an outbreak of measles in New York's hospitals!  So in fact, it's possible to advertise this victory, and yet measles continues to be imported into the United States, where vulnerable populations may be exposed and come down with the virus.  

2. Despite the anti-vaccine movement, nation-wide immunization rates for the primary VPDs haven't recently reduced.  The U.S. Centers for Disease Control and Prevention's survey of vaccinations from 1995 to 2011 do not show (in the aggregate) statistically significant downward trends in vaccinations. 

So again, if we aggregate vaccination trends at the national level, we aren't making a compelling case. 

3. This highlights the important point that community vulnerability - not national vulnerability - is our starting point for action and communication. Why? Because as community members, we should and can take action in our local communities. And furthermore (fortunately!) we don't yet have compelling statistics upon which we can make a compelling case for action. However, we can talk about vulnerability - and risk. 

In 2010, a localized outbreak in California of 9,000 pertussis cases represented one-third of all pertussis cases nationwide. In addition to the waning effectiveness of the current vaccine, it also appears that clustering of unvaccinated individuals played a role. Census districts with a statistically significant higher number of exemptions (referred to as an 'exemption cluster') were 2.5 times more likely to also be in a pertussis outbreak cluster. 

Outbreaks are related to the immunity of the population - driven by, for example, who has been vaccinated or has been previously exposed to the disease. The more that unvaccinated (and presumably vulnerable) people are clustered in a community, the higher the chance they will contract the disease, turning it into an outbreak.  

This diagram (credit: National Institute of Allergies and Infectious Diseases) shows the basics of how a community's composition can affect the likelihood of an outbreak: 

4. We need to bring the data visualizations and the messages down to the local level. The real story is local. Since, fortunately, most localities do not have a history of VPD outbreaks, we have to think about compelling ways to report and show risk.  

So here, to satisfy the brief, we thought about ways to present statistics in terms of the community - in this case, the potential for exposure to others. We wanted to illustrate the connectedness of the community, and the implied consequences of behavior. We imagined a kind of Public Service Announcement (PSA) scorecard for each community, by disease, where the centerpiece visual would be the connectedness of a single infected child to their community, showing the geometric effect where many more could be exposed:

And overall, support the message of consequence in the context of a community. 
To support the PSA scorecard, we relied on discussions from The Journal of Infectious Diseases, the CDC's MMWR reports, and West J Med's report of a 1990 California outbreak of measles to generate the statistics and assumptions embedded in this PSA. We are not epidemiologists or health workers, so this is only a placeholder for what might be more appropriate statistics and better handling by said professionals! It does assume, however, that at least some of the the county or district health departments in the United States would be giving thought to the following statistics or calculations: 
  1. Immunization rates in their community;
  2. Estimated 'R' rates of diffusion/transmission, especially in school systems based on attendance and classroom conditions;
  3. The likelihood of infection rates, based on #1 and #2;
  4. Estimated hospitalizations and deaths based on their age and health demographics;
  5. Average hospital and other related medical expense statistics.
It's a strong message, and a worst case scenario. Although we've qualified some of the statements with hypotheticals, it may be excessive. We assume that health departments have to find the right balance between developing strong language that encourages community health-mindedness, versus sensitivity to those who truly have medical exemptions or other significant religious concerns.  

And, importantly, we assume that county and district health departments would have the resources to collect, compile and regularly produce not only the statistics #1 - #5, but also to be able to produce and distribute the information in the format we've provided above. So, we think of it as a starting point, but perhaps the actual implementation of the solution might have to be iterative and even more grassroots. 

And finally - it goes back to the issue of whether a media organization with a national reach can effectively describe this issue in national terms. Our conclusion: it's valuable in terms of bringing attention to the issue, but the real value, as it often turns out, is illustrating what it means to you and me. 

What are your thoughts? Is this sensible? Excessive? Something else? 

We said this at the beginning: this is NOT the forum to debate whether there is a link between vaccination and autism. It's rather the forum to debate the effectiveness and validity of the original visualization, and our proposed alternatives. Please limit your comments to those on-topic. 

- Michael Thompson, Vivian Peng, Adam Vigiano

1 comment:

  1. If we are hoping to illustrate the correlation between local rates of immunization and local rates of VPD, perhaps a time based graphic needs to be paired with a multivariate graph, with exemptions on the X axis and infections on the Y axis. The resulting worm should have milestone years marked, maybe every ten years to match up with the scale lines on the time graph. Such an illustration would be especially effective if it compared two regions of equal population, one with few exemptions (and few outbreaks if our story is true) and one with many exemptions (and therefore more outbreaks, if our story is true).