Are you health literate?
A person who is health literate possesses the ability to understand written health information and is capable of describing his or her own health in words. Health literacy can be broken down into components; e.g. "prose literacy", "document literacy" and "quantitative literacy" to name only a few. Among these individual skills that comprise health literacy, so called quantitative literacy, or numeracy, is possibly the most critical skill, since numbers - either in text or as graphs - are essential to most health communication. Health literacy, it has been shown on numerous occasions, is an essential determinant of effective doctor-patient communication, health related decisions (e.g. to follow through on medication) and finally overall health.
You, as a reader of this research-oriented blog, are of course health literate and pretty good at thinking in numbers, I will assume; and you might attest. However, it turns out that most people who consider themselves proficient at digesting number based health information, when called upon, often end up performing quite poorly on problems requiring numeracy.
In fact, a study report published in 2003 found that although 71% of their sampled subjects considered themselves to be "good with numbers", only 2% of those 71% achieved a perfect score on a three question numeracy test.
To fully appreciate that number-based health information is not always as simple as "take one pill twice a day", consider this example from a study by Paul Slovic and others:
Suppose you have a close friend who has a lump in her breast and must have a mammogram. Of 100 women like her, 10 of them actually have a malignant tumor and 90 of them do not. Of the 10 women who actually have a tumor, the mammogram indicates correctly that 9 of them have a tumor and indicates incorrectly that 1 of them does not. Of the 90 women who do not have a tumor, the mammogram indicates correctly that 81 of them do not have a tumor and indicates incorrectly that 9 of them do have a tumor. The table below summarizes all this information. Imagine that your friend tests positive (as if she had a tumor), what is the likelihood that she actually has a tumor?
The answer to the above problem is 50%, and- let's face it - this is not immediately evident even to people with higher level education. Indeed, two years ago, a research team around Gerd Gigerenzer of the Berlin-based Max Planck Institute provided the health profession with somewhat of a wake-up call (and helping hand), when they showed that even medical doctors themselves are often not fully capable of interpreting relatively straight-forward numeric health information.
Here is an example:
Assume you conduct breast cancer screening using mammography in a certain region. You know the following information about the women in this region:
The probability that a woman has breast cancer is 1% (prevalence)
If a woman has breast cancer, the probability that she tests positive is 90% (sensitivity)
If a woman does not have breast cancer, the probability that she nevertheless tests positive is 9% (false-positive rate)
A woman tests positive. She wants to know from you whether that means that she has breast cancer for sure, or what the chances are. What is the best answer?
- A. The probability that she has breast cancer is about 81%.
- B. Out of 10 women with a positive mammogram, about 9 have breast cancer.
- C. Out of 10 women with a positive mammogram, about 1 has breast cancer.
- D. The probability that she has breast cancer is about 1%.
Out of 160 Gynocologists tested, only 21% got the correct answer (C); [which the highly quantitative reader may have identified as a rate that is below the rate expected by pure chance guessing...]
I don't intend to get you depressed by reporting on all the troubles that inadequate health literacy can and does cause for individuals and society (although you can read up on that here), as I would rather leave you with the more upbeat notion that numeracy is not really a difficult skill to learn and improve upon. For example, Gigerenzer and his colleagues, in their study, discuss a number of easy and effective numeracy training methods for physicians and the health care profession in general.
Instead, the greater difficulty with numeracy seems to be in convincing people that it is indeed an essential skill for today's society. Indeed, I actually recall once overhearing a conversation in which an adult explained to a young girl that "...essentially, all the math you need in normal, everyday life, you learn by 3rd grade...coming to think of it: you don't even really divide that often, so it might be 2nd grade even..."
The adult in the above conversation was of course (I hope) joking, but I believe that there does exist insufficient appreciation of numeracy as an absolutely necessary skill for everybody in "normal, everyday life".
As far as health care decisions are concerned, I think the importance of quantitative literacy could hardly be more obvious, and considering current efforts for health care reform, and the ongoing trend towards greater sharing of responsibility between patient and physician, one should expect that numeracy will only become more of a defining element for personal health in the future.
Below I list a couple of numeracy related statistics, and if you care for one more example of poor numeracy skills in regard to health and health care reform you might want to look at this "Pinocchio-earning" error in Rudy Giuliani's 2007 campaign.
For the not-so-faint of heart, here then are the promissed numeracy statistics [cited from Reyna, Diekmann, Nelson and Han (2009)]:
- According to a 2007 report on literacy 41% out of a total 9000 high school seniors performed at a below-basic level, 37% performed at a basic level, 20% performed at a proficient level, and 2% performed at an advanced level. This means that a substantial proportion of 12th graders did not have the basic mathematical skills required to, for example, convert a decimal to a fraction.
- In a theme that echoes across multiple national assessments, scores differed among subgroups.
- For example, Asian and Caucasian students performed better than African American, Hispanic, and American Indian students.
- Nearly half the adult U.S. population could not identify and integrate numbers in a lengthy text or perform a numerical task requiring two or more sequential steps. Therefore, many adults lack the skills necessary to read a bus schedule to determine travel time to a clinic appointment or to calculate dosage of a child's medication based on body weight according to label instructions.
- Among racial and ethnic subgroups, Hispanics and African Americans had the lowest average health literacy: Sixty-six percent of
- Hispanics and 58% of African Americans performed at a below basic or basic level of health literacy.
Main References:
Reyna VF, Nelson WL, Han PK, & Dieckmann NF. (2009) How numeracy influences risk comprehension and medical decision making. Psychological bulletin, 135(6), 943-73. PMID: 19883143
Gigerenzer, Gerd. (2007-11) Helping Doctors and Patients Make Sense of Health Statistics. Psychological Science in the Public Interest, 8(2), 53-96. DOI: 10.1111/j.1539-6053.2008.00033.x
