Over the last decade, health literacy has become a vibrant area of research. Investigators have elucidated the prevalence of limited health literacy and the relationship of limited health literacy with patients' knowledge, health behaviors, health outcomes, and medical costs, as summarized in reports by several prominent organizations.1–4 This special issue of JGIM devoted to the topic of health literacy is further evidence of the wide and diverse audience interested in this field.
Ironically, as the field of health literacy has expanded in scope and depth, the term “health literacy” itself has come to mean different things to various audiences and has become a source of confusion and debate. In 1999, the American Medical Association's Ad Hoc Committee on Health Literacy defined health literacy as “the constellation of skills, including the ability to perform basic reading and numerical tasks required to function in the health care environment,” including “the ability to read and comprehend prescription bottles, appointment slips, and other essential health-related materials.”2 The definitions used by Healthy People 20105 and the Institute of Medicine (IOM)3 were similar: “The degree to which individuals have the capacity to obtain, process, and understand basic health information and services needed to make appropriate health decisions.” These definitions present health literacy as a set of individual capacities that allow the person to acquire and use new information. These capacities are relatively stable over time, although they may improve with educational programs or decline with aging or pathologic processes that impair cognitive function.6
Others have argued that if health literacy is the ability to function in the health care environment, it must depend upon characteristics of both the individual and the health care system. From this perspective, health literacy is a dynamic state of an individual during a health care encounter. An individual's health literacy may vary depending upon the medical problem being treated, the health care provider, and the system providing the care.
Some also view health knowledge as part of health literacy. For example, the IOM expert panel divided the domain of “health literacy” into (1) cultural and conceptual knowledge, (2) oral literacy, including speaking and listening skills, (3) print literacy, including writing and reading skills, and (4) numeracy. The American College of Physicians Foundation recently advertised a set of informational cards that physicians could give to their patients to “raise their level of health literacy.”7 From this perspective, health literacy is an achieved level of knowledge or proficiency that depends upon an individual's capacity (and motivation to learn) and the resources provided by the health care system.
All these perspectives represent reasoned ideas based on different orientations to the problem. Nevertheless, the lack of shared meaning for the central term in a field is obviously problematic. For example, there has been confusion and disagreement between the authors of research articles or grants and reviewers. It is not surprising that experts disagree about how health literacy should be measured as it may be that they are not really talking about the same underlying construct. If health literacy is a capacity of a person, measures of an individual's reading ability and vocabulary are appropriate. In contrast, if health literacy depends on the relationship between individual communication capacities, the health care system, and the broader society, measures at the individual level are clearly inadequate. If knowledge is part of the definition of health literacy, this too must be measured.
To address this problem, I will first present a conceptual model of the domains of health literacy and the relationship of health literacy with health outcomes, and suggest possible terms that may be used to describe these domains. This model is designed to supplement the models of health literacy presented within the IOM report to allow more specific and precise discussion of measures of health literacy. I hope this will serve as a first step in a longer process of achieving a shared terminology for researchers and other experts in the field, as recommended in the IOM report. I will then review available measures of these domains and discuss which measures may be most useful in research and clinical practice.