Uncertainty and graphicacy How should statisticians, journalists, and designers reveal uncertainty in graphics for public consumption? Alberto Cairo* INTRODUCTION outside of the cone’. In January 2012, I moved to Florida to teach Apparently, many people either don’t read or at the University of Miami. One of the first don’t understand such an explanation. Scientists recommendations I got from local friends was have described the many ways that common to always pay attention to forecasts during readers misinterpret the map (Broad et at., 2007). hurricane season. For instance, some see the cone of uncertainty as the actual size and scope of the storm, the ‘cone Hurricane forecasts are often shown to the public of death’(sic). People living in Pensacola who read with a map tracking the likely path of the storm, Figure 2 might decide to take limited protection surrounding the point estimates with a ‘cone measures because they think, wrongly, that they of uncertainty’ of increasing width, based on are outside the predicted reach of the hurricane. a decade of past forecast error. For the sake of clarity and to explain some crucial challenges, I Moreover, even if someone familiar with designed a fictional Category 5 hurricane and the elementary principles of uncertainty, error, corresponding map. (Figure 1) and risk interprets the map correctly, there are essential elements that aren’t disclosed. The first Hurricane maps are often accompanied by a time I saw a cone of uncertainty, I immediately caption that says, ‘the cone contains the probable assumed that it represented a 95% confidence path of the storm centre, but does not show the level: I guessed that, based on previous hurricane size of the storm. Hazardous conditions can occur paths, scientists were telling me that 95 out of FIGURE 1 A fictional hurricane and its cone of uncertainty (*) University of Miami Outlook Report 1 Uncertainty and graphicacy FIGURE 2 \ When presented with \ the cone of uncertainty, some readers see the -.- boundaries of a storm. 8PMTuesday l..--...s,-;-8PM Monday St.Pttt-i.,- ....... G ulf .., 8PMSunday A\ ic.,,w....... HurricaneCAIRO ( category 5) ,. 100 times, the path of my namesake hurricane I began thinking about how we could better would be within the boundaries of the cone of convey the uncertainty without using the cone. uncertainty. Figure 3 is based on a series of lines showing different possible paths, coloured with a darker- I was shocked when I discovered my mistake. The lighter gradient proportional to higher and lower confidence level of the cone of uncertainty is just probabilities. 66%. Translated to language that normal human beings like me can understand, this means that 1 Then I realized that this didn’t address one of out of 3 times the path of the hurricane could be the challenges of the original map: It does show outside of the cone. That’s a lot. I can’t help but possible paths the hurricane could take, but it connect this 1/3 forecast to Donald Trump’s victory doesn’t say anything about its possible diameter, in the 2016 presidential election. Many models had which is something that can also be estimated. given him exactly that chance (others gave him The problem? If we overlay the storm itself over 15%, which is also quite high, roughly like rolling its possible paths, we may experience a strong any single number on a 6-sided dice), but many backfire effect in the form of “scientists know Americans were surprised anyway. nothing! This thing could go anywhere!” (Figure FIGURE 3 An alternative map of the hurricane path forecast 2 Outlook Report Uncertainty and graphicacy FIGURE 4 Overlaying the possible size of the storm may be more confusing than helpful 4), even if this is exactly the reality of the forecast graphs, or data maps. On one hand, representing model. the fuzziness of data is essential, the ethical thing to do for scientists, designers, and journalists. On Being incapable of creating anything helpful, I the other hand, we may be doing it for audiences concluded that sometimes it might be better who don’t really grasp what they are seeing, to just communicate a clear message to people, either because they don’t understand uncertainty like in Figure 5, edited to make it appropriate for or because they have little knowledge of the audiences of all ages (Saunders and Senkbeil). grammar and vocabulary of visualization. THE BIG CONUNDRUM: They lack ‘graphicacy’, the term I favour to refer to GRAPHICACY AND graphical literacy. UNCERTAINTY In the past decade, there has been an ongoing This personal story illustrates the main problem I debate in the visualization community about see in communicating uncertainty to the public, the best ways to visualize uncertainty. In a broad particularly through visual means like charts, overview of the discussion, Bonneau et.al. (3) FIGURE 5 A clearer message to the public? Outlook Report 3 Uncertainty and graphicacy defined uncertainty as the ‘lack of information’ of probabilities. That’s especially true of the due to factors like randomness (aleatoric sophisticated but fallible models and simulations uncertainty) or lack of knowledge (epistemic by which scientists attempt to peer into the uncertainty) and described three sources of it: climate future. To say this isn’t to deny science. It’s the sampling of the data, the models based on to acknowledge it honestly. it, and the visualization process itself. They then described several popular methods of revealing The Times received complaints about the first half uncertainty. Being a visualization professional and of this paragraph. Stephens’ ‘modest’ increase of scholar myself, I’m an advocate for using these 0.85 degrees in average temperature is likely the methods and inventing others. largest and fastest—it happened in little more than a century—in the past 10,000 years (Marcott, However, the second part of the aforementioned 2013) (5). problem worries me much more: Most people can’t wrap their head around elementary notions The second half of the paragraph got less of uncertainty and visualization. attention, though, perhaps because it sounds reasonable to uninformed ears, even being misleading, too. What Stephens conveniently MISUNDERSTANDING forgot to mention is that, with no exceptions I’m UNCERTAINTY aware of, all models predicting climate change- On April 28, 2017, Bret Stephens, a conservative related variables such as CO2 concentrations, writer notorious for his denialist positions on global temperatures, and sea level rise have climate change, published his first column in The indeed large degrees of uncertainty, but they all New York Times. It was titled “Climate of Complete also point in the same direction: upward (Figure 6). Certainty” (4) and its main point was that because Another convenient omission is that uncertainty all forecast models are faulty, we should hold cuts both ways: future sea level rise, temperatures, judgment about what measures to implement or CO2 emissions could be lower than predicted now to prepare for a future in which temperatures but, with equal probability, they could be higher. may be higher and sea levels may rise. Stephens’ column illustrates the fact that a good Here’s a representative paragraph: chunk of the general public—this includes journalists—sees science as either ‘indisputable’ Anyone who has read the 2014 report of the facts or ‘fallible’ probabilistic models that aren’t Intergovernmental Panel on Climate Change better than mere opinions. knows that, while the modest (0.85 degrees Celsius, or about 1.5 degrees Fahrenheit) warming That kind of binary thinking is pervasive, and it of the earth since 1880 is indisputable, as is the needs to be addressed at all educational levels: human influence on that warming, much else How do we teach people from a younger age that passes as accepted fact is really a matter that science is always a probabilistic work in FIGURE 6 Sea level rise according to the IPCC report of 2013. Two scenarios, called RCP8.5 and RCP2.6, are shown in red and blue, with their corresponding uncertainty (66% confidence). 4 Outlook Report Uncertainty and graphicacy progress but, as faulty and limited as it is, it’s also MISREPRESENTING by far the best set of methods we have to fathom UNCERTAINTY reality? How do we make the public accept at last A common misconception about visualization is that any assertion in science is always imperfect, that it consists of pictures that can be interpreted incomplete, and likely to evolve —but also that a intuitively. Many believe this because they scientific theory is never a ‘theory’ in the common conceive of visualizations as mere decorative sense of the word, equal to mere ‘opinion’? illustrations and are used to seeing just bar graphs, Sometimes, uncertainty is completely overlooked, time-series line graphs, pie charts, choropleth even if people are aware of its existence. The maps, and proportional symbol maps. They following is a case I discuss in one of my books consider them ‘easy to read’ because they are about data visualization (6). On December 19, 2014, graphic forms with a history of hundreds of years. the front page of Spanish national newspaper El My guess is that the process of widespread País read “Catalan public opinion swings toward adoption of graphic forms follows a trickle-down ‘no’ for independence, says survey” (7). process: (a) a pioneer invents a way of encoding Historically, the population of Catalonia has been and showing data, (b) a small community of more or less evenly divided between those who experts adopts it, (c) eventually the media want the region to become a new country and tentatively tries to use it as well, (d) by being constantly exposed to the new graphic form, the those who don’t, with a slight majority of the general public begins seeing it as ‘intuitive’.