By Florence Kizza

June 17, 2008

Does 30,000 Americans sound like a lot?  How about .01 percent of the U.S. population?

They’re both the same number of people.

How do you present numerical information? According to research by Kansas State University associate professor of psychology Gary Brase, people find percentages and simple fractions easiest to understand. At the same time, people perceive absolute frequencies (like 30 thousand Americans) as greater numbers than fractions or ratios, even when they represent the same amount.

So, says Brase, if you want to persuade, use whole numbers and large references, such as the U.S. or world population. On the flip side, use percentages to inform.

"Take the numbers of people who have a rare disease,” he says. “The percentage could be a tiny amount. But it also could be an impressive number if you consider a large population. You get something that sounds like an important issue."

Following this example, the flip side would be saying that a person has a .0001 percent chance of getting that disease. "People really are not understanding the numbers," says Brase. "All they get out of that information is that it's a really, really tiny amount."