Lee et al. BMC Public Health 2010, 10:614 http://www.biomedcentral.com/1471-2458/10/614 (2) to examine the associations of low health literacy with self-rated physical and mental health status and health care utilization (outpatient clinic visits, hospitali- zation, and emergency room visits). The results would help to confirm if low health literacy is indeed a world- wide health threat, even in a country where the literacy rate is 97.8% and where 22.48% of the adult population has a university degree [17]. Furthermore, we could learn how health literacy contributes to health status and health care utilization in an equitable health care system. Implemented in 1995, Taiwan’s national health insurance system has increased the coverage from 57% to 98% of the population. The system has also expanded access by waiving copayments for the very poor, veter- ans, and aboriginal populations [18]. Methods Sample In 2008, a survey was conducted to assess health literacy in a national sample of Taiwanese adults using the Mandarin Health Literacy Scale (MHLS) [19]. Subjects in the survey were selected based on the Taiwanese household registration system and using a multi-stage stratified, probability-proportional-to-size sampling strategy [20]. A total of 1,967 adults aged 18 and older were selected and contacted by mail or phone for parti- cipation in the survey. Excluding non-responders (sub- jects who refused or could not be reached after five attempts of contact) and subjects who had uncorrectable vision and hearing problems and who were cognitively impaired, 1,492 adults voluntarily participated in the survey. The response rate was 75.8%. Respondents and non-respondents were not different statistically in terms of age and gender, and formal education. Ethical Considerations The protocol for the national survey was approved by the institutional review board at the National Health Research Institutes in Taiwan. In the letter and the phone message to potential participants, we explained the purpose of the survey and asked for their voluntary participation. Those who agreed to participate were scheduled for an in-person interview conducted by a trained interviewer. Before the interview, the interviewer first explained the purpose of the survey, the study par- ticipants’ rights, the risk and benefit of participation, and our plan to protect the confidentiality of study par- ticipants. Further, a signed informed consent was obtained prior to the interview. Data Collection Previous research suggests that illiterate subjects may feel embarrassed about not being able to read and may be uncomfortable taking the self-administered health Page 2 of 8 literacy test, which requires the respondent to read and answer a battery of health related questions [21,22]. To avoid embarrassment, at the beginning of the interview, we asked the respondents to read aloud a brief text as a way to identify those who were illiterate or unable to read. Those respondents (N = 162) who were unable to read were not asked to complete the self-administered health literacy test and received a zero score. The remaining respondents took the health literacy test and were scored according to their performance on the test. All respondents, whether or not they took the health lit- eracy test, answered all the remaining survey questions, administered by an interviewer, regarding socio-demo- graphic attributes, health status, and healthcare utiliza- tion. On average, the interview took around 40 minutes to complete. Measurement The MHLS is a reading and numeracy instrument designed to assess health literacy in Mandarin Chinese or Standard Chinese [19]. The scale contains 50 items, of which 33 test the comprehension of health-related texts and 17 assess numeracy skills. In a random sample of 323 Taiwanese adults, the scale was found to have a high cor- relation with years of formal education, suggesting high convergent validity. It was significantly associated with reading habit, health knowledge, and receipt of assistance with reading written health materials, indicating good predictive validity. Furthermore, it had high internal reliability (Cronbach’s alpha = 0.95) and split-half relia- bility (Spearman-Brown correction = 0.95). In the current study sample, the internal reliability of the scale was 0.88. Following Tsai and colleagues [19], we classified the respondents into three health literacy levels: inadequate (0-30), marginal (31-42), and adequate (43-50). Socio-demographic attributes included age, gender, educational attainment (years of formal schooling), household income, and residential location (metropoli- tan city, mid-size city, small city, rural/remote area). Health status was assessed by asking respondents to self-rate their physical and mental health over the past six months on a 5-point Likert scale, ranging from 1 (very poor) to 5 (excellent). Health care utilization was measured by asking respondents to answer yes or no to (1) whether they had at least an outpatient visit in the previous 3 months, (2) whether they ever visited an emergency room (ER) in the last year, and (3) whether they were ever hospitalized in the last year. Statistical Analysis Descriptive statistics (mean, SD, and percentage) were performed to examine the level of health literacy in the sample as a whole and by socio-demographic attributes. For descriptive analysis, age was classified into 18-24