When reporting on changes in numbers, such as state funding, crime rates, and opinion poll results, it’s important to tell the audience how much a number has increased or decreased over time. However, before you can do that, you need to know the difference between “percentage change” and “percentage point change.”
“Percent change and percentage point change get confused all the time,” says Jennifer LaFleur, senior editor at The Center for Public Integrity, who has taught classes and workshops on using statistics in news for more than a decade. She also teaches data journalism at American University.
That’s why we created this tip sheet, with the help of LaFleur. Together, we’ve created four tips to help journalists master these key math concepts.
1. Note that “percentage change” is the rate of change. Use “percentage point” to indicate the amount of change.
We use “percentage” to describe how much a number has changed from a previous number.
As an example, let’s say state legislators set aside $30 million to fund a new highway safety program in 2021. This year, they budgeted $38 million.
Based on that information, we can say that funding for the road safety program increased by almost 27% between 2021 and 2022.
While you can do the math yourself with these step-by-step instructions, it’s easy to find a percentage change calculator online.
When comparing percentages, use “percentage points” to describe the difference between them. For example, there is a difference of 27 percentage points between 17% and 44%.
It’s worth noting that the Associated Press style calls for using the “percentage” symbol in news stories but writing “percentage point.”
2. Be very careful when comparing percentages because this is where many people make mistakes.
When you add or subtract percentages, for example, when you subtract the percentage of children diagnosed with autism in 1981 from the percentage diagnosed in 2021, describe the result using percentage points.
“If you’re comparing two percentages, they’re percentage points,” says LaFleur.
If a local county health department reports that its percentage of children diagnosed with autism increased from 1% in 1981 to 5% in 2021, it is correct to say that the diagnosis rate increased by 4 percentage points during that period.
The rate did not rise 4%. In this scenario, the diagnosis rate jumped 400%, or five times.
Because this type of error is common, LaFleur encourages journalists to check percentage change figures in government reports and other documents, including news stories from journalists in the same media outlet.
“Part of the problem is that often there is no one in the newsroom who is detecting [these types of errors],” she explains. “A reporter could have done it for years and not realize what they were saying was wrong.”
3. When covering a story based heavily on numbers, look for ways to remove some numbers without sacrificing meaning or context. For example, instead of reporting that enrollment at a local college increased by 100%, say that it doubled.
Because stories with lots of numbers can confuse and overwhelm audiences, and some people avoid them, choose carefully which numbers you want to highlight. Both the Poynter Institute and the Donald W. Reynolds Center for Business Journalism recommend no more than three numbers per paragraph.
LaFleur suggests replacing some numbers with words to help your audience understand the information quickly. Many people will know right away what you mean when you say a number has doubled, tripled, or quadrupled. Because it’s less common to say that a number increased by 100%, 200%, or more, some people may need to stop and do some math to figure out what that means.
“I always advise people to keep it as simple as possible,” says LaFleur.
4. If you need to improve your math skills, get training. A strong understanding of key math concepts helps journalists spot misinformation and math errors.
Journalism and higher education organizations offer a variety of online courses, in-person trainings, and other resources to help reporters and editors brush up on math skills and develop new ones. Here are some:
The Poynter Institute offers the “Certificate in Mathematics for Journalists,” a four-hour online course that costs $29.95. Participants get a certificate upon completion.
Journalists can enroll in free data and numeracy courses on the Coursera and edX online learning platforms.
Investigate Reporters and Editors often host workshops focused on statistical literacy during their annual conferences. At the IRE’s annual data journalism conference in 2021, LaFleur and her colleague Jaimi Dowdell of Reuters led the session, “Tackling statistics in your story.”
Temple University mathematician John Allen Paulos highlights the importance of mathematical literacy in a column he wrote for ABC News in 2004. He explains how a math error in news coverage of a plan to partially privatize Social Security minimized the impact of the plan.
“Usually in print and almost always on television, the proposal is said to require that 2% of Social Security taxes be diverted to private accounts,” he writes. “However, looking a little further, you can find some stories that point out that the 6.2% of the average American’s taxable income that goes to Social Security taxes will be reduced to 4.2%. That’s a 2 percentage point cut, not a 2% cut, but a 32% cut! This will leave a huge hole in Social Security income for current retirees.”
Paulos then wrote the book, “A Mathematician Reads the Newspaper,” published in 2013. In it, he examines news coverage, pointing out logical fallacies and other ways numbers can be misleading.
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Source: news.google.com