- How Science Works
- Sources and Experts: Where to Find Them and How to Vet Them
- Making Sense of Science Stats
- Editing for Story
- Editing Controversial Science
- Holding Science to Account
- Covering Health Care
- Climate and the Environment
- Fact-Checking Science Journalism: How to Make Sure Your Stories Are True
Illustrating Complex Science Stories
- The Role of Visuals in Science Journalism
- The Process of Building Science-Centric Graphics
- Strategies for Using Visuals to Put Breaking Science in Context
- Special Considerations for Data Visualization
- Uncertainty and Misinformation
- Editorial Illustration, Photography, and Moving Images
- Additional Reading and Resources
- About the Author
- Social Media and Reader Engagement
- Popular Science
- Op-Eds and Essays
- About This Handbook
Helping Readers Understand the Numbers
By Elisabetta Tola / 7 minute read
Stand-alone figures can be impactful, but they often lack necessary context. What does it mean, for example, that about 650,000 people in the United States die each year from heart disease? It’s a big number, and that’s a lot of people. In fact, it’s the leading cause of death in the U.S., representing about a quarter of all deaths. But, should that be alarming to us? To provide context, it’s helpful to provide a comparison.
Perhaps we should look at the United Kingdom, which has a similar diet and standard of living to those in the U.S. In the U.K., about 170,000 people die each year from cardiovascular disease. The U.S. looks pretty bad by that comparison. But the percentage of all deaths in the U.K. that are attributable to heart disease, about 27 percent, is a shade higher than that in the U.S.
Of course, this is a function of the differences in overall population size. The U.S. has about 330 million people, and the United Kingdom is just shy of 68 million. So, in terms of the percentage of the overall population, about 2 people out of every thousand die of cardiovascular disease in the U.S., compared with 2.5 in the United Kingdom. Turns out, the U.S. is actually a little better in that respect when the countries’ populations are taken into account.
As an editor, the “So what?” question is a critical one when looking at data. What does this stat mean? What is it saying? Is it significant, surprising, enlightening? Don’t fall into the trap of thinking that numbers in and of themselves are meaningful. They still must be explained, described, and contextualized.
Percentages, Rates, and Ratios
A percentage is just a specific ratio — a comparison to 100. But that doesn’t mean it’s the only one to use. Sometimes other denominators can be useful, like 10 or, as in the example of the death rates above, 1,000. Or, even 1, as in per capita comparisons.
For instance, if you wish to calculate and compare New York’s and Texas’s energy consumption, you could look at the total consumption in each state. Both New York and Texas are big and populous. But how many people use that energy is what matters a lot. The best way to compare is to divide each population’s overall energy consumption, to get a figure per capita. That would give you a comparable result and one that readers find easier to relate to.
Just be sure your comparison is a number that makes intuitive sense. Saying the cardiovascular death rate in the U.S. is 0.0028 per capita may be true, but good luck finding anyone who understands what that means.
One common mistake comes when people try to compare percentages. If you compare the expansion of Brazilian agricultural land from 1965 to 2015, you would see that it grew from 20% to 28%. One way to describe that difference is as an 8 percentage-point increase. Note, however, that this not the same as a “percentage change.” If you wanted to express the change that way, you would have to follow the “NOO” rule (new minus old, with the result divided by old). In that case, you would calculate 28 – 20 = 8. Then calculate 8 ÷ 20 = 0.4. That produces the percentage increase: 0.4 * 100 = 40%.
Translating Big and Small Numbers
Analogies and metaphors are two more tools for making numbers relatable. For instance, our DNA is a text composed of four acids, which we represent as the letters A, C, G, and T. In all, a DNA strand is a chain of 6.5 billion base pairs of those acids. So, written out, that would be 6.5 billion A, C, G, and T characters. That’s a pretty big number, which is tough for most people to grasp. To provide context, one could compare a DNA strand to War and Peace. The novel contains roughly 2.5 million characters, meaning that each of our cells contains a text that is as long as 2,600 copies of Tolstoy’s magnum opus.
Small numbers, too, can be difficult to comprehend. Take the numbers used when talking about climate change, such as the amount of carbon dioxide in the atmosphere (400 parts per million) or the goal of holding temperature change to 2 degrees Celsius. In both cases, historical context can bring meaning that the small that figures themselves cannot. This passage from a Time magazine article does that well:
We live enshrouded by an atmospheric greenhouse of gases and water vapor that has maintained life-supporting conditions for hundreds of millions of years; CO2 is part of that mix. But over the past three million years our greenhouse system has been highly unstable. The record of CO2 trapped in polar ice reveals that over the last 800,000 years, during dramatic swings between ice ages and warm periods, CO2 has oscillated between 180 and 280 ppm. In the last rapid warm-up from the most recent glacial period, CO2 jumped to 260 ppm, and then oscillated around 275 ppm. Since then, for about 9,000 years, our climate has been relatively stable. Agriculture, civilizations and states emerged, and global population grew from several million at the end of the last Ice Age to 1.2 billion in 1850.
Repeat after me: Numbers do not tell stories on their own. Your choice of wording and the figures you choose to highlight serve to put a particular perspective on the data. This is known as the framing effect — thoroughly described by that Nobel laureate Daniel Kahneman in his book Thinking, Fast and Slow — and it has a substantial impact on readers and listeners; our decision-making depends enormously on the way facts are presented. For example, saying a type of surgery has 70% chance of success sounds very different than saying three people out of 10 will very likely die during said surgery. Slight changes in wording and framing can lead people to interpret the information very differently.
Not only are data not inherently objective, but they can be downright subjective in certain circumstances, such as when crucial statistics or context is omitted. It is essential to describe the source of the data and what conflicts of interest might be lurking behind the spreadsheets. Who paid for the research? How were the data collected? What data were excluded? The power of figures to sway public opinion is well known. Just look at the tobacco companies that provided research to downplay the risks — and tout the perceived benefits — of tobacco on human health. We now know that those studies were flawed, but they filled the news and the commercials for years. And of course, they set the template for other companies and industries to follow.
Tips When Writing About Numbers
It should be to our profession’s embarrassment that many journalists take pride in not understanding anything about numbers or math. Yet, as Sarah Cohen points out in the must-have reference book Numbers in the Newsroom, “The fear of numbers marks a reporter as one who can only do part of the job.” Here are a few tips on how to make numbers and math work for you as a journalist:
- Know your universe. Sarah Cohen and Jennifer La Fleur, two award-winning data journalists, say the most important step is to know some of your beat’s basic figures. For example, if you’re editing stories about climate change, you should know your region’s average temperatures, the current concentration of carbon dioxide in the atmosphere (416 parts per million), and the warmest year on record (2019, as of this writing midway through 2020), among other basic statistics. Those editing Covid-19 coverage should have internalized such basic information as the fatality rate (estimated at 1%) and how that compares with other diseases, like influenza (0.1%), SARS (11%) and MERS (35%), as well as transmission rates (or R0), which for the current coronavirus is estimated at 2 to 2.5. Of course, the R0 depends greatly on environmental factors, such as whether or not people are wearing masks and practicing social distancing. The point is, knowing the basic stats and facts will allow you to catch errors and put a finer point on stories.
- Use large and small numbers with care. People are terrible at understanding very big and very small numbers. It’s challenging to put a “billion” into context, or to understand how tiny a virus is (less than 100 nanometers). So it’s better to relate numbers to something in people’s experiences. Saying 800 million people do not get enough to eat each day is easier to understand when phrased as “more than twice the population of the United States goes to bed hungry every day.” Likewise, find creative ways to visualize the very small. For example, in describing the size of bacteria, you could say, “about 150,000 bacteria can fit on the tip of one hair.”
- Beware of false precision. Imagine a scientist saying a dinosaur skeleton is 100 million years old. Five years later, would you say that skeleton is 100,000,005 years old? Of course not. The “hundred million” figure, like many measures in nature, is an estimate with some inherent uncertainty, not a precise figure. Using “exact” figures with decimals to the hundredths place is rarely the best way to present numbers. It is often much better to use a good approximation within the appropriate order of magnitude. Rather than “23.7%,” go with ‘’slightly less than one out of four.’ Likewise, 44% becomes “more than 4 in 10.”
- Don’t overuse numbers in a paragraph. Ideally, you should write concise sentences and short paragraphs, describing the sense of data without necessarily displaying the numbers, unless they are needed. Sarah Cohen suggests reducing the number of digits in your copy to improve the use of those you do use. As a rule of thumb, she says it’s worth reducing the number of digits in a paragraph to eight. As an example, saying, “More than 200,000 people in the U.S. died from coronavirus in 2020” already has 10 digits. It’s a rule of thumb, though, and not a law. Just be judicious and use digits only when necessary to explain the ideas.