Health literacy (the ability to recognise and comprehend basic health information) and numerical
literacy (the ability to understand numerical information and conduct basic numerical calculations) are
vital considerations in the development of health information messages. In the U.S., 21% of adults are
functionally illiterate and 27% are marginally illiterate. This problem is illustrated in a recent U.S.
study in which 46% of adults incorrectly estimated probability related to a coin flip, and 80%
incorrectly converted 1 in 1000 to 0.1% (Davis et al., 1998; Schwartz et al., 1997). Table 2 outlines
some of the cognitive differences between high-literate and low-literate adults in terms of their
processing of written health risk information