How Good Are We With Numbers?
Bandolier
103 featured a study that looked at literacy attainments in rheumatoid
arthritis patients. Literacy is especially important because these patients
often have complicated medication regimens. The study found that one patient in
six would, at best, struggle with patient education material, and one in 20
could not read prescription labels. We now have some studies looking at
numeracy, both in medical students and patients.
But
first we need to have some understanding of what is numeracy. The dictionary
definition is one of competence in mathematical skills to allow us to cope with
everyday life, but also includes understanding mathematical terms from graphs,
charts, or tables. Fortunately health numeracy has been provided with a set of
definitions [1].
Various
levels of health numeracy have been defined (Table 1). The four levels start at
the most basic, with statistical numeracy being that degree of numeracy that we
would expect from most doctors, and quite a lot of other health professionals.
Table 1: Some definitions of health numeracy
Concept | Definition |
Health numeracy | The degree to which individuals have the capacity to
access, process, interpret, communicate, and act on numerical, quantitative,
graphical, biostatistical, and probabilistic health information needed to
make effective health decisions |
Basic numeracy | Having sufficient skills to identify numbers, and to
make sense of quantitative data requiring no manipulation of numbers. An
example would be identifying the correct numbver of pills to be taken, data
and time of appointments, using a phone book |
Computational numeracy | The ability to count, quantify, compute, and
otherwise iuse simple manipulation of numbers, quantities, items, or visual
elements in a health context so as to function in everyday situations. An
example would be using nutritional labels correctly |
Analytical numeracy | This involves the ability to make sense of
information, as well as higher functions like inference, estimation,
proprtions, percentages, frequencies, and equivalent situations. Information
may be from multiple sources, and an example would be deterimining whether an
analytical result was within the normal range, or understanding graphs |
Statistical numeracy | An understanding of basic biostatistics involving
probability statements, skills to compare different scales (Probability,
proportion, percent), to critically analyse quantitative information like
life expectancy or risk, and understanding concepts like randomisation and
blinding. An example would be making choices between treatments based on
standard outcomes of relative or absolute risk |
Numeracy in medical students
One
way of measuring numeracy is to ask a few simple maths questions, and see how
many correct answers you get. It does not need to be an intensive examination,
and one set of questions used in studies of medical students and patients is
shown in Table 2 [2]. Most of us would expect to get the right answers to these
three questions, on simple probability, and converting frequency to percentages
and back again. The level is that of basic and computational numeracy in Table 1.
Table 2: Three simple questions to test numeracy
Question | ||
Imagine that we flip a coin 1000
times. What is your best guess about how many times the coin would come up heads? |
||
In the lottery, the chance of winning a
prize is 1%. What is your best guess about how many people would win a prize if 1000 people each buy a single ticket to the lottery? |
||
In the publishing sweepstake, the chances
of winning a car is 1 in 1000. What percent of tickets to the publishing sweepstake wins a car? |
These
questions were answered by 62 first-year medical students at the University of
North Carolina at Chapel Hill medical school who attended a risk-communication
seminar. Most students answered all three questions correctly, but 5% (1 in 20)
answered only one or none correctly (Figure 1).
Figure 1: Numeracy as measured in medical students and patients
Students
were also given information about treatment choices, with results presented in
different ways (relative risk reduction, absolute risk reduction, number needed
to treat, and a combination). Most students (90%) correctly stated which drug
worked better (comparative answer), but only 61% could work out the
quantitative answer. For both, there was a strong relationship with being able
to answer the simple maths questions correctly (Figure 2).
Figure 2: Students' interpretation of quantitative information according to their correct answers to numeracy questions
Numeracy in patients
The
same research group performed the same tests in 257 patients aged 50 to 80
years attending for health care at an internal medicine clinic [3]. The results
for numeracy are in Figure 1, and show that most patients could answer only one
(30%) or no (41%) numeracy questions correctly. It was also true that whatever
way information was presented to them, only 40-60% were able to determine which
of two treatments was better, but fewer than 20% (1 in 5) were able to work out
the quantitative difference.
Comments
There
is not a huge literature on numeracy, but it is likely to be important, and at
least as important as literacy. For instance, a single observational study [4]
showed that patients older than 50 years attending anticoagulation management
units had significantly poorer control of INR when they had low numeracy
skills, while low literacy made no difference.
But
numeracy and literacy have to be taken together. A detailed paper too difficult
to précis [5] asked professionals and public about ways of expressing
results relating to prenatal diagnosis and chromosome abnormalities. There were
huge differences in the way people responded to the same information. For
instance, when asked which of 5% or 1 in 20 sounded bigger, 81% thought 1 in 20
sounded bigger. That paper is certainly worth a read for anyone teaching
communication skills.
The
bottom line, though, is that on limited information, we can identify that many
patients and some professionals have problems with numbers. That puts even more
heat on trying to explain those numbers in ways that people can understand.
References:
- AL Golbeck et al. A definition and operational framework for health numeracy. American Journal of Preventive Medicine 2005 29: 375-376.
- SL Sheridan, M Pignone. Numeracy and the medical student's ability to interpret data. Effective Clinical Practice 2002 5: 35-40.
- SL Sheridan et al. A randomized comparison of patients' understanding of number needed to treat and other common risk reduction formats. Journal of General Internal Medicine 2003 18: 884-892.
- CA Estrada et al. Literacy and numeracy skills and anticoagulant control. American Journal of Medical Science 2004 328: 88-93.
- L Abramsky, O Fletcher. Interpreting information: what is said, what is heard – a questionnaire study of health professionals and members of the public. Prenatal Diagnosis 2002 22: 1188-1194.