Executive Summary
Evidence Report/Technology Assessment: Number 199
The Agency for Healthcare Research and Quality (AHRQ), through its Evidence-based Practice Centers (EPCs), sponsors the development of evidence reports and technology assessments to assist public- and private-sector organizations in their efforts to improve the quality of health care in the United States. The reports and assessments provide organizations with comprehensive, science-based information on common, costly medical conditions and new health care technologies. The EPCs systematically review the relevant scientific literature on topics assigned to them by AHRQ and conduct additional analyses when appropriate prior to developing their reports and assessments.
AHRQ expects that the EPC evidence reports and technology assessments will inform individual health plans, providers, and purchasers as well as the health care system as a whole by providing important information to help improve health care quality.
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Introduction / Methods / Results / Discussion / Future Research / Full Report
Introduction
Health literacy is "the degree to which individuals can obtain,
process, and understand the basic health information and services they need to
make appropriate health decisions." It represents a constellation of skills
necessary for people to function effectively in the health care environment and
act appropriately on health care information. These skills include the ability
to interpret documents, read and write prose (print literacy), use quantitative
information (numeracy), and speak and listen effectively (oral literacy).
Low health literacy is a significant problem in the United
States. In 2003, approximately 80 million adults in the United States (36
percent) had limited health literacy. Rates of limited health literacy in
certain population subgroups were higher. For instance, rates were higher among
the elderly, minorities, individuals who have not completed high school, adults
who spoke a language other than English before starting school, and people
living in poverty. Highlighting the health impact of low health literacy, a
2004 systematic evidence review found a relationship between low health
literacy and poor health outcomes. Specifically, health literacy (measured by
reading skills) was associated with health-related knowledge and comprehension,
hospitalization rates, global health measures, and some chronic diseases.
Given the burden of low health literacy and the potential to
reduce poor outcomes using novel interventions to address it, several national
organizations have called for action. In 2010, the U.S. Department of Health
and Human Services (HHS) released a National Action Plan to Improve Health
Literacy. Additionally, in recent years, several national organizations and
agencies, including the Institute of Medicine, American Medical Association,
National Institutes of Health, and HHS (in Healthy People 2010), have promoted
health literacy as a research priority.
Researchers responded to these calls with new and more
sophisticated work. Thus, to synthesize the increasing volume of literature on
health literacy, the Agency for Healthcare Research and Quality (AHRQ)
commissioned the RTI International—University of North Carolina Evidence-based
Practice Center (EPC) to update its 2004 systematic review examining the
effects of literacy on health outcomes and interventions to improve those
outcomes. In this updated report, we focus on the same Key Questions as the
original report:
- Key Question 1. Outcomes: Are health literacy
skills related to (a) use of health care services, (b) health outcomes, (c)
costs of health care, and (d) disparities in health outcomes or health care
service use?
- Key Question 2. Interventions: For individuals
with low health literacy skills, what are effective interventions to (a)
improve use of health care services, (b) improve health outcomes, (c) affect
the costs of care, and (d) improve health care service use and/or health
outcomes among different racial, ethnic, cultural, or age groups?
In contrast to our earlier report, we concentrate on "health
literacy" rather than "literacy" for several reasons. First, we aimed to be
consistent with recent conceptualizations of health literacy skills that
separately examine print literacy, numeracy, and oral literacy. Second, an
increasing number of newer measures are framed in specific health contexts and
assess condition-related skills. Finally, measures of health literacy, print
literacy (including prose and document literacy), and numeracy are highly
correlated in national samples.
Although we believe our focus on health literacy appropriately
represents the directions of research and policy in this field, we acknowledge
that the literature contributing to this field does not organize itself neatly
within our health literacy framework. For instance, several measures of health
literacy assess a combination of print literacy and numeracy skills, making
distinctions between print literacy and numeracy difficult. Furthermore, the
quantitative skills components of some measures have been extracted and used
independently as measures of numeracy. To simplify this report, we separate
health literacy (including any studies that presume to measure literacy or
health literacy) from those that solely measure numeracy or oral literacy.
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Methods
Changes From Our Prior Review
Our overall goals in this update were to evaluate whether newer
literature was appropriate for answering our Key Questions and to determine
whether earlier conclusions changed. Following discussions with our Technical
Expert Panel, we modified the original methods as follows:
- We broadened our definition of health literacy to be
consistent with the Ratzan and Parker (2000) definition used by Healthy People
2010 and the Institute of Medicine. Thus, our inclusion criteria included
studies that measured numeracy and oral skills of participants.
- We required that studies directly measured the health
literacy of the study population and did not assign health literacy level via
self-report or similarity to other populations.
- To evaluate individual study quality, we incorporated
advances in the methods of conducting systematic reviews.
- We included studies conducted in developing countries as
long as they used an objective measure of literacy or health literacy in their
participants.
- We reviewed knowledge as an outcome only for numeracy and
intervention studies because evidence in the earlier review clearly concluded
that greater literacy skills and higher health-related knowledge levels are
positively related.
- If articles about intervention studies were missing
information about intervention content, we queried the investigators to allow
richer interpretation about what interventions may be effective in mitigating
the effects of low health literacy.
Outcomes of Interest
The logic model in Figure A details outcomes that we included in
our review as well as other conceptually important variables. It draws on
several models of health literacy proposed by researchers in the field and on
an integrated model of behavioral theory called the Integrative Theory. We
applied this model to determine whether studies considered for inclusion had
relevant health outcomes and to guide our presentation of included articles. It
is not, however, a definitive guide to the relationship among variables because
researchers have not explicitly tested many of these relationships yet.
Furthermore, it does not specify the directionality of a good outcome; for some
outcomes, increases represent the good outcome (e.g., adherence, most screening
tests) and for others, decreases represent the good outcome (e.g.,
hospitalizations, mortality). We did not examine outcomes related to attitudes
because of the belief that attitudes result from knowledge, which, as mentioned
above, is not examined in the current report. Further, we did not examine
outcomes related to social norms or patient-provider relationships (e.g.,
shared decisionmaking) because we thought that these variables likely affected
the direction or strength of the relationship between behavioral intent and
health outcomes, rather than laying on the causal pathway. Clearly, however,
empiric work is needed to test these assertions prior to future reviews.
Literature Search
and Retrieval Process
We searched MEDLINE®, the Cumulative Index to Nursing and Allied
Health Literature, the Cochrane Library, PsycINFO, and the Educational
Resources Information Center. For health literacy, we searched from 2003 to May
25, 2010. For numeracy, we searched from 1966 to May 25, 2010. We conducted
keyword searches because no Medical Subject Headings terms specifically
identify health-literacy-related articles. The terms health literacy, numeracy,
and literacy, and terms or phrases related to instruments known to measure
health literacy and numeracy, were the focus of the search. We excluded
editorials, letters to the editor, case reports, and non-English language
studies. We also manually searched reference lists of pertinent review articles
and editorials for additional studies.
Article Review and Data Abstraction
We used standard EPC methods for dual review of abstracts and
full text of articles to determine article inclusion. After determining article
inclusion, one reviewer entered data about studies into evidence tables and a
second, senior reviewer checked information for accuracy and completeness.
Quality Review
Two reviewers independently rated the quality of studies (good,
fair, or poor) using criteria designed to detect selection bias, measurement
bias, confounding, and inadequate power. Reviewers resolved all disagreements
about quality ratings by consensus. We did not consider further any studies
that we rated poor quality.
Data Synthesis and Grading Strength of Evidence
We synthesized the data in our review qualitatively. We did not
have a sufficient number of studies with similar outcomes or similar
interventions to consider quantitative analysis (meta-analysis or statistical
pooling) of data. Furthermore, we primarily discussed information from the current
searches, providing only aggregate summaries of data from our 2004 review. As
part of data synthesis, we paid particular attention to a few issues. First, we
closely examined whether studies accounted for relevant confounding variables
in their analyses. Because the goal of etiologic research focuses on
understanding the relationship between exposures and outcomes of interest, it
is important that confounders are controlled for to determine accurate
estimates of effect. Second, we looked closely at studies that reported the
relationship between both health literacy and numeracy and the same outcome.
This allowed inferences about the relative strengths of the measures on
outcomes. Third, for intervention studies, we looked at common features of
successful interventions and at the impact of interventions on multiple related
outcomes. This allowed inference about the effective components and mechanisms
of health literacy interventions.
The investigative team jointly discussed and graded the overall
body of literature and generated recommendations for future research. For
grading strength of evidence, we used the AHRQ EPC program's approach:
assigning grades of high, moderate, low, or insufficient to the evidence after
considering the domains of risk of bias, consistency, directness, and
precision. We resolved disagreements by consensus discussion.
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Results
Search Results and Included Studies
Our searches of electronic databases and review articles produced
3,496 unduplicated records. Ultimately, for the two main questions, we included
studies rated either good or fair quality: 81 studies (95 articles) addressed
Key Question 1 and 42 studies (45 articles) addressed Key Question 2. Key
Question 1 results are presented separately in relation to health literacy (86
articles) and numeracy (16 articles). Of these, we identify the 7 articles that
address both health literacy and numeracy.
Key Question 1: Relationship of health literacy
to various outcomes and disparities
Sixty-four articles pertaining to this part of Key Question 1 had
cross-sectional designs; 22 were cohort studies. We categorized studies
examining outcomes associated with differences in health literacy level into
two main domains: use of health care services and health outcomes. Strength of
evidence evaluations focused on the relationship between the lowest health
literacy group and the highest. The evidence was sparse for evaluating
differences between those with marginal health literacy (a middle category) and
adequate health literacy (the highest category).
Use of Health Care Services—Health Literacy
Moderate evidence about health care service use showed that lower
health literacy was associated with increased hospitalization (five studies),
greater emergency care use (nine studies), lower use of mammography (four
studies), and lower receipt of influenza vaccine (four studies). Evidence for
all other analyses of health care service use was low or insufficient because
of inconsistent findings or outcomes; this includes studies about colon screening,
Papanicolau (Pap) tests, testing for sexually transmitted infections,
pneumococcal immunization, and access to care.
Health Outcomes—Health Literacy
Lower health literacy was associated with poorer outcomes in
some of the health outcomes examined. A higher risk of mortality for seniors
(two studies) was clearly associated with lower health literacy (high strength
of evidence). Lower health literacy was associated with poorer ability to
demonstrate taking medications appropriately (five studies), poorer ability to
interpret labels and health messages (three studies), and poorer overall health
status among seniors (five studies) (all of moderate strength of evidence). In
these studies, the evidence consisted of all observational studies, generally
with a medium risk of bias and results in a consistent direction.
The strength of evidence for the many other outcomes we
examined—adherence, self-efficacy, smoking, alcohol use, healthy lifestyle,
review of prescription information, HIV risks and sexual behaviors, chronic
disease prevalence, HIV severity and symptoms, asthma severity and control,
diabetes control and related symptoms, hypertension control, prostate cancer
control, quality of life, and costs—was either low or insufficient. The
literature consisted of only a small number of studies, poorly designed
studies, and/or inconsistent results.
Potential moderators and mediators of the relationship between
health literacy and health outcomes were also identified during our review. Two
studies concluded that social support and health care system characteristics
modify the magnitude and/or direction of the relationship between health
literacy and adherence and health literacy and blood pressure control. Four
studies concluded that knowledge, patient self-efficacy, and stigma might act
as mediators or intermediaries in the causal pathway between health literacy
and health outcomes and explain at least some of the negative impact of low
health literacy on these health outcomes. In addition, one study suggested that
health literacy may mediate the effect of education, income, and urbanicity on
health outcomes.
Costs—Health Literacy
Evidence was insufficient to evaluate the relationship between
differences in health literacy levels and costs. The two relevant studies
examined different payment sources (Medicaid and Medicare) and different
populations, and found inconsistent results.
Disparities in Outcomes—Health Literacy
In relation to disparities, health literacy appeared to mediate
the effect of race on several health outcomes. These included conditions that
keep a person from working, long-term illness, self-reported health status,
receipt of an influenza vaccine, physical and mental health-related quality of
life, self-reported health, prostate-specific antigen levels, nonadherence to
HIV medications, and enrollment in health insurance. Health literacy also
mediated differences by both race and gender in the misinterpretation of
medication label instructions.
Key Question 1: Relationship of numeracy to various
outcomes and disparities
In this update, we identified 16 studies examining the
relationship between numeracy and health outcomes. Eleven were cross-sectional
in design. Four studies were randomized controlled trials (RCTs) that analyzed
their data in a cross-sectional manner for this analysis; one study used a
prospective cohort design.
In general, the evidence pertaining to this Key Question was
either low or insufficient given the small number of studies; these studies
often had high risk of bias or, collectively, gave us mixed results.
Use of Health Care Services—Numeracy
Only one study addressed the relationship between numeracy and
use of health care services (low strength of evidence). It reported no effect
of numeracy on up-to-date screening for breast and colon cancer, but it
appeared to be limited by inadequate power to detect a meaningful effect.
Health Outcomes—Numeracy
Relationships between numeracy level and accuracy of risk
perception (five studies), knowledge (four studies), skills taking medication
(six studies), and disease prevalence and severity (three studies) were mixed.
The evidence for the relationship between numeracy and other health outcomes,
such as self-efficacy or behavior, was insufficient to draw conclusions. No study
addressed the costs associated with differences in numeracy level.
Disparities in Outcomes—Numeracy
Two studies examined whether numeracy level mediates health
disparities. Numeracy appeared to mediate the relationship between race and
levels of hemoglobin A1c and between gender and HIV medication management
capacity.
Key Question 1: Comparison of the relationship
of health literacy and numeracy to the same outcomes
Seven studies addressed the effects of both health literacy and
numeracy on various outcomes. Of the seven, only four performed adjusted
analyses on the same outcomes, thereby allowing assessment of whether these
exposures affect health outcomes differently. All suggest that numeracy is more
highly correlated with outcomes than health literacy. However, all must be
interpreted with caution, because the proportion of individuals with low health
literacy was small, raising the possibility of ceiling effects that could
obscure effects in the literacy analyses.
Key Question 2: Interventions to improve low
health literacy
In this update, we included 42 studies of good or fair quality
addressing the effect of interventions designed to mitigate the effects of low
health literacy; of these, 27 were RCTs, 2 were cluster randomized trials, and
13 were quasi-experimental studies. We focused our analyses on 2 separate sets
of studies: 21 that used one specific strategy (single design features) to
lessen the effects of low health literacy and 21 that used a mixture of
strategies combined into a single intervention.
Interventions With Single Design Features
Of intervention studies testing single design features, two
focused on alternative document design, three on alternative numerical
presentation, eight on additive or alternative pictorial representations, four
on alternative media, and seven on a combination of alternative readability and
document design. Additionally, one intervention focused on the effects of
physician notification about patients' literacy status on health outcomes.
Effects were measured primarily in terms of comprehension.
Overall, the strength of evidence for specific design features in
these interventions was low or insufficient. This is attributable, in large
part, to differences in the types of interventions and, subsequently, in the
mix of results. Looking closely within categories of design features, however,
the following specific design features seemed to improve comprehension for
low-health-literacy populations in one or a few studies:
- Presenting essential information by itself (i.e., information on hospital death rates without other distracting information, such as information on consumer satisfaction).
- Ppresenting essential information first (i.e., information on hospital death rates before information about consumer satisfaction).
- Presenting health plan quality information such that the higher number (rather than the lower number) indicates better quality.
- Using the same denominators to present baseline risk and treatment benefit.
- Adding icon arrays to numerical presentations of treatment benefit.
- Adding video to verbal narratives. Additionally, in reexamining data from our 2004 review within these categories, we identified further evidence of potential benefit from using reduced reading level and/or illustrated narratives.
In contrast,
one study raised questions about whether certain design features, such as
colored traffic symbols to denote death rates in hospitals of varying quality
or symbols accompanying nonessential quality information, may actually worsen
health choices among those with low health literacy.
Interventions With a Combination of Features
The strength of evidence for studies combining multiple
strategies to mitigate the effects of low health literacy on either health care
use or outcomes was more variable than it was for single-feature interventions.
Use of Health Care Services
Across all studies in this category, we found moderate strength
of evidence that interventions included in the review changed health care
service use. Specifically, intensive self-management and adherence
interventions appeared to be effective in reducing emergency room visits and
hospitalizations. Additionally, educational interventions and/or cues for
screening increased colorectal cancer and prostate cancer screening (although
we note that the health benefits of additional prostate cancer screening are
not clear).
Health Outcomes
We found evidence of moderate strength that some interventions
changed health outcomes. For instance, intensive disease-management programs
appeared to be effective at reducing disease prevalence/severity. Furthermore,
self-management interventions increased self-management behavior; however, in
the only study that stratified a subgroup analysis by health literacy level,
improvements were sometimes greater for those who had adequate health literacy
and at other times greater for those with inadequate health literacy in
adjusted analyses. The effects of other interventions on other health outcomes,
including knowledge, self-efficacy, health-related skills, adherence, quality
of life, and costs were mixed; thus, the strength of evidence was insufficient.
Components of effective interventions were their high intensity,
theory basis, pilot testing before full implementation, emphasis on skill
building, and delivery of the intervention by a health professional.
Interventions that changed distal outcomes (e.g., health care service use or
health outcomes) appeared to work by affecting intermediate factors, such as
increasing knowledge or self-efficacy, or by changing behavior.
Too few studies addressed the effects of health literacy
interventions on the outcomes of behavioral intent, and disparities to draw any
meaningful conclusions; the strength of evidence is insufficient.
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Discussion
What This Update Adds to the 2004 Review
The results of this review expand our understanding of the
relationship between health literacy and health outcomes in several ways.
First, a majority of studies included in this review performed multivariate
analysis, allowing us to make better estimates of the true effect of health
literacy on health outcomes. Second, new studies have addressed the
relationship between numeracy level and health outcomes. This allows a better
understanding of what it means to be health literate. Third, we identified a
limited body of research that begins to identify variables that may be on a
causal pathway between health literacy and health outcomes. These variables
include knowledge, self-efficacy, and social stigma. Finally, new studies
suggest that health literacy can be a mediator of racial disparities in health
outcomes.
We also learned many new things about interventions to mitigate
the effect of low health literacy. First, we identified several design features
of interventions that were effective in one or a few studies (enumerated
above); they all warrant further study in broader populations. Second,
interventions focused on a broader range of outcomes, allowing us to make
inferences about effect across outcomes. Preliminary examination of these
studies suggests that effective interventions to mitigate the effects of low
health literacy may work by increasing knowledge and self-efficacy or by
changing behavior. Additionally, certain factors appear to be key in making the
interventions effective with respect to distal outcomes (e.g., self-management,
hospitalizations, mortality); these include high intensity, theory basis, pilot
testing before full implementation, emphasis on skill building, and delivery of
the intervention by a health professional (e.g., pharmacist, diabetes
educator).
Limitations of the Literature
As with all systematic reviews, our results and conclusions
depend on the quality of the published literature. Heterogeneity in outcomes,
populations, study designs (or interventions), and measured outcomes was a
problem for both Key Questions. This level of diversity in the knowledge base
precluded us from pooling results statistically.
The limitations of the literature for Key Question 1 studies
included:
- Lack of a priori specification and inconsistent
approaches to creating health literacy and numeracy levels or thresholds in
analyses, hampering comparisons between studies.
- Inconsistent choices of potential confounding variables
in multivariate analyses.
- Small sample sizes, making it impossible for us to
determine whether null findings represented a true lack of effect or simply
limitations in statistical power.
- Studies in just one clinic or in other narrowly defined
patient populations, rendering the applicability of findings to other settings
or populations unknowable.
- Use of health literacy tools that continue to focus
primarily on reading ability.
- The limited number of studies examining potential
mediators of health literacy, such as self-efficacy, knowledge, or beliefs.
- Few studies examining the role of health literacy on
health disparities.
- No studies examining differences in outcomes related to
oral literacy skills.
The limitations of the literature for Key Question 2 studies
included:
- Lack of an adequate control or comparator group in many
studies, limiting the ability to determine the true effect(s) of the
intervention.
- Measurement of multiple outcomes with insufficient
attention to ensure that each had been adequately powered to detect a
difference.
- Testing interventions that combined various design
features to mitigate the effect of low health literacy but offering no way to
determine the effectiveness of individual components.
- Failure to perform adequately controlled subgroup analyses
that would elucidate differential effects of interventions in low- and
high-health-literacy populations.
- Failure to report adequately the intervention design
features that would allow future content analyses of effective interventions.
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Future Research
The field of health literacy has clearly advanced since our 2004
review appeared. The progress has been both conceptual and empirical.
Nonetheless, many opportunities remain for important future research. Such
investigations will improve our understanding of the impact of health literacy
on the use and outcomes of health care and will expand the knowledge base about
the impact of interventions intended to improve health literacy. Our
recommendations for future research involve both better methods and specific
clinical or operational topics.
In examining the relationship between literacy and health
outcomes, investigators should consider:
- Specifying a priori their cutpoints for distinguishing
levels of health literacy and noting the relevance of those levels to (a) the
outcomes and population being studied and (b) the body of similar work in the
field.
- Using health literacy measurement tools that go beyond
health-related literacy and numeracy to capture additional and potentially
critical skills, particularly oral health literacy.
- Ensuring sufficient statistical power to detect
differences among relevant health literacy levels.
- Controlling for an adequate set of potential confounders.
- Improving the applicability of results to broader populations
and settings.
- Further examining potential mediators and moderators of
the relationship between health literacy and health outcomes.
In examining the impact of interventions to mitigate the effects
of low health literacy, investigators should consider:
- Testing novel approaches to increase motivation; improved
techniques for delivering written, oral, or numerical information; and
"work-around" interventions such as patient advocates.
- Determining the effective components of already-tested
interventions that employ a combination of features intended to lessen the
effects of low health literacy. Although a combination of intervention features
has repeatedly been shown to ensure the success of interventions, paring away
ineffective features could save delivery time and result in more cost-effective
delivery.
- Determining the cost-effectiveness of effective programs.
- Determining the effect of practice and policy
interventions. We found almost no studies that addressed such interventions.
Implications of This Report for Clinicians and Policymakers
We anticipate that this update will continue to raise awareness
among clinicians and policymakers alike that low health literacy has a
substantial impact on the use of health care services and health outcomes; it
also hints at the role of health literacy in disparities in utilization or
outcomes among groups defined by various sociodemographic characteristics.
However, little remains known about the direct effect of lower health literacy
on the costs of health care. Addressing the burden of low health literacy that
we have identified warrants the attention of many stakeholders.
We highlight effective interventions that could be implemented in
clinical practice now. Intensive interventions related to medication adherence,
self-management, and disease management delivered by clinical practitioners are
of special interest.
Additionally, for policymakers, we underscore the critical need
for research funding to test practice and policy interventions, particularly
those that, to date, have gone largely untested. The recent HHS National Action
Plan to Improve Health Literacy helps enumerate these and other critical
actions for health care professionals and policymakers to take in addressing
the multifaceted issues involving health literacy in this country.
Return to Contents
Full Report
The executive summary is part of the following document:
Berkman ND, Sheridan SL, Donahue KE, Halpern DJ, Viera
A, Crotty K, Holland A, Brasure M, Lohr KN, Harden E,
Tant E, Wallace I, Viswanathan M. Health Literacy
Interventions and Outcomes: An Updated Systematic
Review. Evidence Report/Technology Assessment No. 199.
(Prepared by RTI International—University of North Carolina
Evidence-based Practice Center under Contract No. 290-2007-10056-I.) AHRQ Publication No. 11-E006. Rockville,
MD. Agency for Healthcare Research and Quality. March
2011. Available at: http://www.ahrq.gov/clinic/tp/lituptp.htm.
Print copies of the summary may be obtained from the AHRQ Publications Clearinghouse by calling 800-358-9295.
Return to Contents
AHRQ Publication Number 11-E006-1
Current as of March 2011
Internet Citation:
Berkman ND, Sheridan SL, Donahue KE, et al. Health Literacy
Interventions and Outcomes: An Updated Systematic
Review, Executive Summary, Evidence Report/Technology Assessment: Number 199. AHRQ Publication Number 11-E006-1, March 2011. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/clinic/epcsums/litupsum.htm
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