shows the full search results. Of the 73 articles that met eligibility criteria, 44 articles informed the key questions for this paper. The main reasons for exclusion were no original data (48% of articles), no health outcome (34% of articles), and no measure of literacy (10% of articles). Study designs included cross-sectional studies (32), cohort studies (9), case-control studies (2), and retrospective case series (1).
The number of participants enrolled ranged from 34 to 3,260. Most studies presented descriptive information on participants’ age, ethnicity, and education; about half reported participants’ income levels. Sixteen studies included information about the participants’ insurance status, but only 4 included insurance in a multivariate analysis.
Literacy was most often measured with the Rapid Estimate of Adult Literacy in Medicine (REALM, 13),11
the Test of Functional Health Literacy in Adults (TOFHLA or the short version S-TOFHLA, 15),12,13
or the Wide Range Achievement Test (WRAT, 6), and characteristics of these instruments are presented in .14
The range and distribution of literacy levels varied widely among studies. Research teams usually analyzed literacy as a categorical variable but tended to use different cutoff levels.
summarizes all identified and included studies and their findings. Of the 44 studies, we graded 25 as good, 16 as fair, and 3 as poor. We generally focus on the good-quality studies here, but when no good-quality study was performed, we discuss the available evidence.
Published Studies Evaluating the Relationship Between Literacy and Health Outcomes
Relationship Between Reading Ability and Knowledge Outcomes
Sixteen studies measured the relationship between reading ability and knowledge of health outcomes or health services ().15–30
Eight were graded as good quality.15–19,21–23
In general, these studies found a positive and significant relationship between reading ability and participants’ knowledge of these health services or health outcomes. Only 2 studies did not find a statistically significant positive relationship18,25
; 1 was clearly underpowered.25
Relationship Between Reading Ability and the Use of Health Care Services
One good-quality cross-sectional study found no statistically significant relationship between literacy and number of self-reported health care visits after adjusting for age, health status, and economic indicators.31
One small, fair-quality cross-sectional study reported that lower literacy patients had 3 times the number of outpatient visits as higher literacy patients, but statistical tests were not reported.32
Screening and Prevention.
Two studies evaluated the relationship between reading ability and health promotion and disease prevention.33,34
In a good-quality cross-sectional study, Scott et al. found that, after controlling for age, gender, race, education, and income, Medicare enrollees with lower literacy had a greater odds of never having had a Pap smear (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.0 to 3.1) and not having a mammogram in the past 2 years (OR, 1.5; 95% CI, 1.0 to 2.2) than patients with higher literacy.33
In the same study by Scott et al., patients with lower literacy were more likely to report not receiving influenza (OR, 1.4; 95% CI, 1.1 to 1.9) and pneumococcal immunizations (OR, 1.3; 95% CI, 1.1 to 1.7) compared to patients with higher literacy after adjustment for age, gender, race, education, and income.33
Two good-quality prospective cohort studies showed, in adjusted analyses, that a lower literacy level was significantly associated with increased risk of hospitalization.35,36
The odds of hospitalization at a public hospital over 1 year were 1.69 times higher (95% CI, 1.13 to 2.53) for patients with lower literacy than for patients with higher literacy, after adjusting for age, gender, race, health status, receiving financial assistance, and health insurance, but not for education.36
In the second study, the odds of being hospitalized among Medicare enrollees were 1.29 times higher (95% CI, 1.07 to 1.55) for patients with lower literacy than for patients with higher literacy after adjusting for age, gender, race/ethnicity, language, income, and educational status.35
Relationship Between Reading Ability and Health Outcomes
Two good-quality studies evaluated the relationship between literacy and medication adherence and found conflicting results.37,38
Two fair-quality studies evaluated adherence to research or therapy visit schedules.39,40
Both Golin et al. and Kalichman et al. measured adherence to antiretroviral therapy for HIV infection in good-quality studies. Golin et al. measured adherence prospectively over 48 weeks using electronic bottle caps, pill counts, and self-reports among 117 patients in a university HIV clinic.38
They found no bivariate relationship between literacy and adherence (r
= .88), and did not perform multivariate analyses. Kalichman et al. measured self-reported adherence in 184 patients; lower literacy was associated with a greater odds of poor adherence (OR, 3.9; 95% CI, 1.1 to 13.4), defined as recall of missing any dose during the previous 48 hours,37
after adjustments for race, income, social support, and education.
One good-quality cross-sectional study found that asthma patients with higher literacy had better metered dose inhaler technique based on measuring the number of steps performed correctly (difference in number of correct steps out of 6 steps = 1.3 steps; 95% CI, 0.9 to 1.7).23
Analyses were adjusted for education and whether the patient had a regular source of care.
One good-quality study21
and 2 fair-quality studies41,42
evaluated the relationship between literacy and smoking. The best study was a cross-sectional study that evaluated the relationship between literacy and smoking practices among 600 pregnant women. The investigators found no difference in the unadjusted rates of smoking according to literacy status, but they did not perform adjusted analyses for relevant confounders.21
study and 2 fair-quality42,44
studies evaluated behavior problems of children or adolescents. Davis et al. studied 386 adolescents from low-income neighborhoods and found that, after controlling for age, race, and gender, youth who were more than 2 grades behind expected reading level (Slosson Oral Reading Test) were more likely than others to carry a weapon, take a weapon to school, miss school because it was unsafe, and be in a physical fight that required medical treatment than youth who were at the expected reading level.43
and 1 poor-quality41
study found that mothers with better reading skills were more likely to breastfeed their children.
Three good-quality cross-sectional studies assessed the relationship between reading ability and diabetes outcomes.22,46,47
Ross et al. found no important correlation between WRAT scores for children ages 5 to 17 years with type 1 diabetes and glycemic control (r
= .1, unadjusted).46
However, the parent's score on the National Adult Reading Test (NART) was correlated with the child's glycemic control (r
= .28; P
= .01) even after adjusting for the age and gender of the child, duration of diabetes, daily insulin dose, the child's literacy score, and social class.
Williams et al. found that A1C levels were somewhat higher among those with lower literacy than those with higher literacy, but the difference was not statistically significant (8.3% vs 7.5%; P
= .16) and they did no adjusted analyses.22
Additionally, A1C values were available for only 48% of the sample because the study was designed to assess diabetes knowledge.
Schillinger et al. measured the relationship between reading ability and glycemic control or self-reported diabetes complications among 408 patients from a public hospital internal medicine or family practice clinic and controlled for age, race/ethnicity, gender, education, language, insurance, depressive symptoms, social support, diabetes education, treatment regimen, and diabetes duration.47
Among patients with low literacy (n
= 156), 20% had “tight” glycemic control (A1C < 7.2), compared with 33% of those with higher literacy (n
= 198) (adjusted OR, 0.57; P
= .05). In adjusted models, patients with lower literacy were also more likely than those with higher literacy to report retinopathy (OR, 2.33; 95% CI, 1.2 to 4.6) and cerebrovascular disease (OR, 2.71; 95% CI, 1.1 to 7.0). Statistically significant relationships were not found for lower extremity amputation (OR, 2.48; 95% CI, 0.74 to 8.3), nephropathy (OR, 1.71; 95% CI, 0.75 to 3.9), or ischemic heart disease (OR, 1.73; 95% CI, 0.83 to 3.6), although the lack of statistical significance may be attributable to the rarity of these events, because the magnitude of association was similar.
Two good-quality studies evaluated the relationship between reading ability and hypertension.22,48
One used a cross-sectional design; the other, a case-control design. Neither identified an independent relationship between reading ability and presence or control of hypertension. In a bivariate comparison, Williams et al. found that patients with low literacy had higher systolic blood pressures than those with higher literacy (155 mm Hg vs 147 mm Hg; P
= .04; n
However, after adjusting for age they found no relationship.
In a study by Battersby et al., patients with hypertension did not have statistically significant differences in literacy scores compared with their age-, race-, and gender-matched controls without hypertension (n
= 180) (Schonell graded word reading test: cases 78.4, controls 81.3).48
Three fair-quality cross-sectional studies evaluated the relationship between reading ability and control of HIV infection.27,28,49
These studies, which were all performed by the same research group, reported on different outcomes in an overlapping sample of HIV-positive patients in Atlanta, Georgia. The studies had mixed results: some results confirmed a relationship, others did not.
Depression or Other Emotional Conditions.
Two good-quality cross-sectional studies,50,51
2 fair-quality cross-sectional studies,32,49
and 1 poor-quality cross-sectional study20
evaluated the relationship between reading ability and depression and found mixed results. One additional fair-quality cross-sectional study evaluated reading ability and “emotional balance.”52
All these studies used self-report questionnaires to measure depression; 2 evaluated depression in the context of specific chronic diseases (rheumatoid arthritis32
and HIV infection49
The largest good-quality study assessed depression among Medicare managed care patients using the Geriatric Depression Scale.51
This study found an unadjusted OR of being depressed of 2.7 (95% CI, 2.2 to 3.4) for those people with lower literacy compared to those with higher literacy as assessed by the S-TOFHLA. However, after adjusting for demographic, social support, health behavior, and health status factors, the adjusted OR of 1.2 (95% CI, 0.9 to 1.7) was much smaller and no longer statistically significant. In this case, adjustment for health status may have effaced a true relationship (overadjustment) because depression is known to affect health status directly.
Another good-quality study found in unadjusted analysis that women who had lower literacy skills were more likely to be depressed than women with higher literacy skills (estimated relative risk = 1.60; 95% CI, 1.21 to 2.12).50
No relationship was detected between women's literacy and depression or antisocial behavior among their children (P
The three lower-quality studies support a modest relationship between reading ability and depression.20,32,49
Arthritis and Functional Status.
One fair-quality cross-sectional study of 123 consecutive patients with rheumatoid arthritis found no relationship between functional status and reading ability.32
One fair-quality case-control study evaluated the relationship between reading ability (WRAT) and migraine headaches. There was no difference in the reading levels of the 32 children with migraine headaches and the 32 control children without migraine headaches.53
Prostate Cancer Stage.
One good-quality cross-sectional study evaluated the relationship between reading ability and stage of presentation of prostate cancer.54
Men with poorer reading ability (n
= 66) were more likely to present with late-stage prostate cancer than those with better reading ability (n
= 146) (55% vs 38%; P
= 0.022; calculated OR, 2.0; 95% CI, 1.1 to 3.7). After adjusting for race, age, and location of care, the investigators found that the relationship between literacy and stage of presentation was smaller and no longer statistically significant (OR, 1.6; 95% CI, 0.8 to 3.4), suggesting important confounding between race and literacy in this population.
Global Health Status Measures.
Four good-quality cross-sectional studies evaluated the relationship between reading ability and a global health status measure ().3,31,55,56
Three studies found an association between poorer reading ability and poorer health status3,31,55
; the fourth found no relationship.56
Weiss et al. assessed global health status using the Sickness Impact Profile (SIP) in a group of relatively young participants (mean age 29 years).55
After adjusting for age, gender, ethnicity, marital status, insurance status, occupation, and income, people who scored below the fourth grade level on the Test of Adult Basic Education and Mott Basic Language Skills Program scored worse on the SIP (10.4 vs 6.0; P
Baker et al. examined self-reported health status among 2,659 patients at 2 public hospitals by asking whether their health was excellent, good, fair, or poor.31
After controlling for age, gender, race, and socioeconomic indicators, they found that patients with lower literacy had about 2 times the odds of reporting poor health compared to patients with higher literacy. Gazmararian et al. also examined the relationship between literacy and self-reported health status. They queried 3,260 patients enrolled in a Medicare managed care health plan about their health status using the same question. In their bivariate comparison, patients with lower literacy were more likely to self-report fair or poor health than patients with higher literacy (43% vs 20%; P
In contrast, Sullivan et al. measured general health status among patients with type 2 diabetes using the Medical Outcomes Study Short Form-36 (SF-36)56
; they assessed literacy using the Questionnaire Literacy Screen (QLS), which was being developed at the time of the study. In an unadjusted analysis, they found no difference in scores on the SF-36 according to whether the subject “passed” or “failed” the QLS.
Relationship Between Reading Ability and Costs of Health Care
One study of good quality examined the relationship between reading ability and cost of health care.57
It found no relationship between literacy and Medicaid charges gathered from Medicaid records (r2
= .0016; P
= .43). In subgroup analyses examining inpatient care, outpatient care, and emergency care, the investigators did not identify any relationship between literacy and charges. Most patients in this study enrolled in Medicaid because of pregnancy rather than medical need or medical indigence. A subsequent statistical analysis of nonpregnant patients (n
= 74) found that the 18 patients with a reading level at or below third grade had higher mean Medicaid charges than the 56 who read above the third grade level ($10,688 vs $2,891; P
Disparities in Health Outcomes or Health Care Service Use
Only one good-quality cross-sectional study directly examined the role of reading ability as a mediator of disparities in health outcomes or health care service use. In this study, black patients were significantly more likely than white patients to present with late-stage prostate cancer (unadjusted 49.5% vs 35.9%; P
= .045; calculated OR, 1.7; 95% CI, 1.0 to 3.2).54
After adjustments for literacy, age, and location of care, the odds ratio was smaller and no longer statistically significant (OR, 1.4; 95% CI, 0.7 to 2.7). The authors suggest that literacy may be mediating some of the racial difference in stage of presentation for prostate cancer. As noted earlier in the results, literacy was also not statistically significant after adjustment for covariates.