# Numeracy

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In the context of health literacy, numeracy describes a person’s ability to understand clinical and public health data. We use numeracy to make decisions about screening and treatment options. There are two types of numeracy: subjective and objective. Subjective numeracy is a person’s reported confidence in understanding mathematical data. Objective numeracy measures a person’s actual math skills.

Read this collection of selected research to examine how numeracy affects a person’s ability to understand visual displays of risk and how health care and public health professionals can frame numbers to enhance patients’ understanding of health information. Overall, findings from these studies suggest numeracy plays a critical role in people’s ability to make informed decisions about their health. Public health and health care professionals can improve how they communicate with people who have low numeracy.

Visual displays of risk

van Weert and colleagues (2021) studied graphical format preference and understanding of graphical representation of risk information in younger and older adults in the Netherlands. The researchers divided study participants into two groups—adults younger than 65 and adults 65 and older—and assessed preferences and understanding through six graphical formats: bar, clock, pie, table, sparkplug, and pictograph (also called icon array). Study findings suggest that clock, bar, and pie charts are the preferred format for graphs across both age groups, but pie and clock scored among the lowest for understanding. Tables scored the highest for understanding. Bar graphs also performed well for understanding in younger and older adults.

Hamstra and colleagues (2015)  studied how 420 men, median age of 52 years, used graph data to understand recurrence of prostate cancer over time. Participants were randomized to view one of four different graph types (pie, bar, pictograph, or line), with either one number (those affected) or two numbers (those affected and unaffected). Participants who viewed the pictograph with two numbers demonstrated the highest knowledge of cancer recurrence based on reading graph data. Numeracy level was associated with a study participant’s ability to answer questions based on using line graphs or pie charts. Numeracy level was not associated with a participant’s ability to answer questions based on using pictographs or bar charts. Study findings suggest a combination of numbers and graphical displays, specifically pictographs, can successfully communicate information about risk. Despite the success of pictographs, respondents reported that pictographs were their least preferred graphical format.

Before releasing a graphical display of data, test the display with a sample of the intended audience and get their feedback.

Zikmund-Fisher and colleagues (2011)external icon studied how numeracy influences decisions about treatment for breast cancer recurrence in a sample of 1,781 women ages 40-74. Researchers used pictographs (also called icon arraysexternal icon) to present treatment choices all at once to one group and in a sequential pattern to a second group. All participants understood risk better when presented with a sequential choice of therapy compared to those who received information about all choices at once. Among women with high numeracy, chemotherapy was selected less often when presented with a sequential pattern and risk of recurrence was low. Women with low numeracy demonstrated greater sensitivity to risk reduction with a sequential pattern compared to seeing all choices at one time. Study findings suggest presentation of risk data in addition to sequencing choices makes it less likely a person will feel overwhelmed and accept treatment based on misunderstood information.

Decision aids

Ancker and colleagues (2022) conducted a systematic literature review to study best ways to effectively present numerical health information. They found disagreements in the literature regarding the best way to present probability and other quantitative concepts. They also discovered inconsistencies in the vocabulary that researchers use to communicate numerical information. The authors indicate that for a communication method to be considered effective, it requires answering the question, “Effective at what?”

To address these issues, Ancker, et al., organize terminology used in these studies into three taxonomies: the taxonomy of outcome measures, the taxonomy of data presentation formats (e.g., percent vs. ratio, type of graph), and the taxonomy of data structures (e.g., trade-offs, probability concepts vs. quantity concepts, number of variables). Their taxonomies allow them to identify different best practices for different conditions. The authors are using these taxonomies to develop a decision aid that communicators and researchers can use when creating educational and informational materials for health-related decision-making.

Smith and colleagues (2016) studied the association between people’s numeracy skills and their knowledge and attitudes about a colorectal cancer screening test called the fecal occult blood test or FOBt. The sample comprised 964 adults aged 45-59 years. Participants received a mailed booklet about colon cancer screening information. There were no differences in numeracy by age, gender, self-reported health, or marital status. Participants identified as low numeracy were more likely to report less education than those with higher numeracy. Those with low numeracy were more likely to have negative attitudes towards the FOBt and to agree with questions about practical attitudes such as challenges related to keeping stool in the house, privacy, and time. Low numeracy also suggested less likelihood to seek screening or cancer-related information and lower knowledge of colorectal cancer screening. Study findings suggest text-based materials tailored for people with low numeracy can be developed to describe what the numbers mean and explain the perceived and actual risks and benefits of a procedure or treatment.

Lopez-Perez and colleagues (2015)external icon examined the relationship between numeracy and decisions about treatment options for localized prostate cancer in a sample of 279 men over age 50. Researchers provided a written scenario describing prostate cancer and two common treatment options including data on risks and benefits for each. Researchers assessed objective numeracy, a person’s actual ability to solve math problems. Treatment choices were the same between men who had been screened for prostate cancer and those who had not been screened previously. Higher numeracy was associated with selecting active surveillance (AS) over radical prostatectomy (RP). Mortality risk for both options is similar but short-term effects vary. RP reduces the potential for cancer growth over time but risks include urinary incontinence and erectile dysfunction. Men who choose AS risk having the cancer grow more quickly, making it harder to treat in time, but the short-term effect is transitory urinary incontinency. Study findings suggest addressing the information needs of people with low numeracy promotes understanding of long- and short-term risks and associated quality of life following a treatment decision.

Provider-patient communication

Janz and colleagues (2016)external icon surveyed a sample of patients with early-stage breast cancer about their doctors’ communication regarding cancer recurrence after surgery. More than half of the study participants (n=3930) reported doctors used words and numbers to communicate risk. Respondents with low numeracy reported less discussion about risk of recurrence. Women who thought they had zero risk of recurrence or overestimated their risk of recurrence were less likely to report having conversations with their doctor about risk. The authors caution that verbal communication alone may lead to using words that are not precise (e.g., unlikely, low risk) and using numbers alone may create a barrier for people with low numeracy. Study findings suggest using both words and numbers to explain risk. Learn how to describe what the numbers mean and explain the perceived and actual risks and benefits.

Ciampa and colleagues (2010)external icon examined the relationship between numeracy and provider communication related to colorectal cancer screening in a sample of adults over age 50. The authors assessed subjective numeracy (i.e., reported confidence in numeracy skills) and objective numeracy (i.e., actual numeracy skills). Participants with low subjective and objective numeracy were older, non-White, reported less educational attainment and had lower annual income. Respondents with low subjective numeracy were less likely to report their provider ensured understanding, answered their questions, or engaged them in decision making. Respondents with low objective numeracy reported the opposite. Ciampa and colleagues explain this discrepancy by citing different communication needs among those with low subjective and objective numeracy. Low subjective numeracy was also associated with less screening practices. Study findings suggest the importance of assessing perceived confidence and actual ability to understand risk data and tailoring communication accordingly.

Numeracy and health outcomes

Petrova and colleagues (2016)external icon studied how numeracy influences a person’s decision to seek medical care when experiencing acute coronary syndrome (ACS). The sample of 102 participants was surveyed five days after experiencing ACS and had a mean age of 58 years. Increased survival rate for ACS is associated with seeking care within 1 hour of symptom onset. In this study, researchers measured objective numeracy by asking participants to solve basic math questions. Subjective numeracy was self-reported based on participants’ perceived numerical abilities. Participants with high objective and subjective numeracy reported more education and were more likely to seek care within the first 50 minutes of experiencing cardiac symptoms. Higher objective and subjective numeracy were also associated with having fewer obstructed arteries. Higher objective numeracy was associated with shorter delays in seeking care. Study findings suggest that people with low numeracy are at greater risk of delaying their decision to seek medical care and experiencing negative health outcomes as a result.

Summary

You can support the information needs of people with low numeracy by 1) assessing perceived confidence and actual ability to understand risk data and 2) tailoring communication using a combination of text and visual formats that address perceived and actual risk.