Health Literacy

Working With Numbers

Article from the Boston Globe’s On Call Magazine, June/July 2004

By Helen Osborne, M.Ed., OTR/L
President of Health Literacy Consulting

“Medicine is inherently numerical,” says Lisa M. Schwartz, MD, MS, general internist and senior research associate at the VA Medical Center in White River, Vermont. Patients need to understand numbers in order to make health decisions based on risk and benefit information.

Schwartz, who is also associate professor of medicine in the department of community and family medicine at Dartmouth Medical School in Hanover, New Hampshire, says numbers convey the magnitude of risks and benefits more clearly than words. For example, the term “likely benefit” may have different meanings to people depending on their point of view. A health professional might understand a likely benefit as one that occurs at least 10 percent of the time. A patient, especially one seeking hope, might instead assume that he or she has at least a 70 percent chance of benefiting from a particular intervention. “There is a huge range of what words can mean,” says Schwartz. “The only way to understand magnitude is to use numbers.”

But numbers are hard for many people to understand. The 1992 National Adult Literacy Survey (the most recent data available) looked at quantitative literacy—defined as “the knowledge and skills required to apply arithmetic operations … [and use] numbers embedded in printed materials.” The survey found that 47 percent of the adults in the U.S. have inadequate quantitative skills. This means that they are likely to have significant difficulty with, or be unable to use, number-based information presented in complicated formats like schedules, tables, or graphs.

In addition, many people have difficulty using numbers to calculate concepts like probability. In an informal study, Schwartz asked a group of health professionals what “.1%” means and found that about 25 percent of the respondents got the answer wrong. When her colleague asked the same question of the general public, about 75 percent of respondents were incorrect. Indeed, many people do not know that “.1% probability” means a probability of “1 out of 1,000.”

Misunderstandings like this can have a significant impact when people make health decisions based on numbers. Health professionals can help. Schwartz has some suggestions for ways to help patients better understand and use numbers in health information.

Know why you are using numbers. Numbers can be used to tell people what they need to know. For instance, they can express the differences in risks and benefits among comparable treatment options. They can also be used to motivate people. For example, numbers can emphasize the benefits of not smoking or of losing weight. Knowing what you hope to achieve when you use numbers will help you decide what numbers to present. It will also make it easier to present data in a balanced and fair way—using all the relevant data, not just the most compelling numbers.

Additionally, discussing and explaining numbers takes time—time that may be better spent in other ways. Schwartz recommends that health providers talk about numbers when risk information is very important. For instance, when patients need to understand the magnitude of benefits and harms of their treatment choices, numbers are needed. But numbers may not be necessary when you are talking about the importance of screening or health-promotion activities. Instead, stories or anecdotes may be more effective in communicating these types of health messages.

Use numbers when there is good data. A good time to use numbers is when the absolute magnitude is impressive, says Schwartz. This means that the data holds up in study after study. When the science is strong, she says, it is usually worth the time to help people understand the numbers and what they mean. A good example would be explaining data from randomized trials for breast-cancer treatment.

Sometimes, the data is less clear. In nutrition studies, for instance, it is often hard to isolate the effect of certain foods or to determine whether health benefits are due to diet, exercise, or both. In cases like these, Schwartz recommends that health professionals highlight in more general terms how good nutrition helps, rather than introduce numbers that may be somewhat questionable.

There may be times when patients ask for numbers and the data is uncertain. In such cases, be honest. Say the data is not clear. You can, however, go on to talk about what you believe to be true based on the available evidence.

Create risk charts. Risk charts are simple, low-tech, visual tools that put disease risk into context. Schwartz and her colleagues have created examples of risk charts that show how many people out of 1000 will die of a particular disease within the next 10 years. There are separate charts for men and women, smokers and non-smokers—with risk data for people ages 20 to 90. The charts not only are appealing to look at, but easy to understand. You can find examples and more information about risk charts at the Journal of the National Cancer Institute’s Web site:;94/11/799?ij

Use benchmarks for comparisons. Many people have difficulty understanding the magnitude of specific risks. You can sometimes help people understand numbers by giving them a benchmark or point of comparison. For example, a benchmark might be the risk of being hit by a meteorite or the chance of being in a minor car accident. Benchmarks like these, Schwarz says, give people a way to understand magnitudes by anchoring unfamiliar concepts to ones they can understand.

Help patients be informed users of data. Offering guidance in the following ways can help reduce the difficulty of working with complex numbers:

  • Teach patients the meaning of key terms like “risk” and “probability.”
  • Explain how to assess the quality of data and other scientific information.
  • Educate patients about what to look for in risk statements, such as: What is the risk? What is the time frame? Who is at risk?
  • Help patients put risk information into context, such as not giving undue weight to sensational events.
  • Encourage patients to ask a lot of questions and have a healthy skepticism about numbers.

Numbers are powerful communication tools, but when used improperly, they can raise  people’s sense of vulnerability and fear rather than help them maintain their health. Scaring people with numbers can be counterproductive. Helping them know what the numbers mean moves them beyond fear so they can understand what they need to know about their health.

How to Find Out More

Lisa M. Schwartz, MD, MS, is a general internist and senior research associate at the VA Medical Center in White River, Vermont, and also associate professor of medicine in the department of community  and family medicine at Dartmouth Medical School in Hanover, New Hampshire. You can reach her by e-mail at

  • National Center for Education Statistics (1993). Adult literacy in America: a first look at the results of the national adult literacy survey. Washington DC: US Department of Education. Available at
  • Schwartz LM, Woloshin S, Welch HG (1999). “Risk communication in clinical practice: putting cancer in context.” Journal of the National Cancer Institute Monographs No. 25: 124 – 133.
  • Woloshin S, Schwartz LM, Welch HG (2002). “Risk Charts: Putting cancer in context.” Journal of the National Cancer Institute, Vol. 94, No. 11: 799-804. Available online at;94/11/799?ij

Article reprinted with permission from On Call magazine and published by a division of Boston Globe Media.