Because of its well-established role in health outcomes and health disparities, HL is an important factor to study in public health and epidemiological research13
. To our knowledge, this is the first study to test the performance of self-reported HL questions among an ethnically diverse, English and Spanish-speaking population, and to compare the performance of the questions between language and other patient characteristic subgroups. We found that three self-reported HL questions could identify those with inadequate, and inadequate plus marginal HL within this ethnically diverse, English and Spanish-speaking population with a moderate degree of discrimination. The “confident with forms” question performed best among the individual items and within both language and all other patient characteristic subgroups. The summative scale performed similarly to the individual “confident with forms” question.
Our findings build on previous studies of the three self-reported HL measures. As in prior studies17,18,20
, the “confident with forms” question performed the best out of the three questions. In contrast to prior work, we found that both the “confident with forms” question and the summative scale could discriminate moderately well between those with inadequate plus marginal vs. adequate HL, in addition to inadequate HL, for both English and Spanish speakers. For the “confident with forms question” Chew et al found a C-index of 0.72 for inadequate plus marginal HL while we found a C-index of 0.81 for the overall sample. This is important because marginal HL, in addition to inadequate HL, has been associated with poor health outcomes including mortality and health disparities4,12,26
. Because dose response associations have been found between HL level and poor patient outcomes,31
some investigators may want to identify both literacy level subgroups. Our results also mirror those of prior studies in finding similar performance between the “confidence with forms” item and the summative scale17
In stratified analysis by language, the C-indices for the “confidence with forms” question were similar for Spanish and English speakers. However, the item seemed to have higher sensitivity but lower specificity among Spanish speakers at every cut point. The optimum cut point for the “confident with forms” question for English speakers that maximized both sensitivity and specificity was “somewhat” or less, while for Spanish speakers the optimum cutpoint was “a little” or less. These findings may be the result of cultural variation and /or Spanish-speaking participants responding to the ‘confident with forms” question for forms not only written in Spanish, but also in English. As such, researchers may want to consider different cut points for English and Spanish-speaking subgroups.
The utility of the “confident with forms” question and summative scale among the Spanish speakers in our population may also be affected by the relatively high prevalence of language concordant patient-physician dyads in this clinical setting and the ubiquitous access to Spanish transcription and translation services22
. Patient–physician language concordance has been shown to be a powerful determinant of patient satisfaction with communication and may have leveled the playing field with their English-speaking counterparts in terms of patients feeling confident with forms22
. As such, the self-reported measures in this population may have been detecting true HL deficits rather than those related to language discordance or limited English proficiency.
Because of a prior lack of brief, validated measures of HL for diverse populations, some have suggested using demographic characteristics to estimate HL32
. This approach does not permit the ability to assess the independent effects of HL beyond demographic characteristics. This is important because HL levels have been shown to vary widely within patient demographic subgroups6
. Therefore, we contend that independent measurement of HL, for example with the “confident with forms” question or summative scale, would contribute substantially to epidemiologic and clinical research. In the clinical setting, screening for limited health literacy is controversial, with the current expert recommendations against routine screening32–34
. However, in selected clinical situations, such as the prescribing of high-risk medications, screening for limited health literacy has been advocated, and the use of a single-item screener would be more feasible in busy clinical settings than standard literacy assessments19
While imperfect in their precision, the summative scale, and specifically the single “confident with forms” question, have some clear advantages over direct, longer HL measurements. They are brief and can be administered via telephone. Our group has recently field-tested these questions both individually and as a scale within a large sample of diverse diabetes patients and have demonstrated robust, independent associations with a range of outcomes, including perceived need for self-management support35
, higher rates of hypoglycemia36
, and lower patient use of electronic health records37
. While these studies did not assess performance of these items across demographic sub-groups, these associations lend support to the items’ predictive validity.
Our study has some limitations. First, we included only patients with poorly controlled diabetes, which may limit generalizability to healthier populations. Second, this study was conducted at four sites within one county health care system and may not reflect regional differences. Third, in our practice environment there is excellent access to translation services and many physicians and staff speak Spanish. Results may differ for Spanish-speaking patients in different linguistic environments. Finally, our results reflect the criterion validity of the self-reported HL questions, i.e., their relationship with a gold-standard HL measurement. Further work is needed to establish predictive validity of these questions in relation to health outcomes of interest.
In summary, although limited HL is associated with a range of health outcomes, it is often not feasible to measure directly in clinical, epidemiologic, or public health studies because standard measurement tools are lengthy and cannot be administered by telephone. Our study suggests that the single self-reported “confident with forms” question or the summative scale of the three self-reported HL questions discriminate diverse English speakers and Spanish speakers with adequate HL from those with inadequate and inadequate plus marginal HL to a degree that warrants application and further assessment in epidemiologic and clinical research involving diverse populations.