Participants
In all, 5304 citizens aged 15 to 69 years who had lived in the sampled regions for more than 6 of the previous 12 months were selected in Wuhan, and 5205 were interviewed from November to December 2018 in this cross-sectional survey. Participants were excluded from the survey if they refused to participate or were unable to communicate. The questionnaire was self-administered. However, if participants were unable to complete the questionnaire due to impaired vision, a poor understanding, a lower education level or other similar reasons, an interview was conducted as an alternative. In this case, the investigators would complete the questions in a neutral manner on behalf of the participants. An incentive was provided to encourage them to participate in the survey, and participants were sent small gifts (20 packages of toilet paper) as a reward for participating. The response rate of the questionnaire was 98.1%. A multistage stratified random sampling method [22] was used to recruit participants. The sampling method was divided into three stages. First, residential committee villages or administrative villages were regarded as primary sampling units (PSUs), and 204 monitoring points (residential committee villages or administrative villages) were selected from the whole city using the probability-proportional-to-size sampling (PPS) method. Then, 26 households were randomly selected from each chosen monitoring point. Finally, one eligible resident from each household was selected randomly using a Kish selection table [23]. This study was approved by the Ethics Committee of Wuhan Centre for Disease Control and Prevention, China. Written informed consent was obtained from all participants.
Questionnaire
Data were obtained in face-to-face interviews with the HLQ (2018 edition) [16] developed by the Chinese Ministry of Health. As Chinese is the common and official language of China, the questionnaire was prepared in simplified Chinese. The questionnaire consisted of three parts: (1) family support questionnaire, (2) basic personal situation, and (3) health literacy content. Based on the “Chinese Resident Health Literacy—Basic Knowledge and Skills (Trial)” and existing public health issues in China, the health literacy section (50 questions) was further categorized into three aspects and six dimensions. The three aspects were (1) knowledge and attitudes (KAA, 22 questions), (2) health-related behaviour and lifestyle (BAL, 16 questions), and (3) health-related skills (HRS, 12 questions). The six dimensions were (1) scientific views of health (SVH, 8 questions), (2) infectious diseases (ID, 6 questions), (3) chronic diseases (CD, 9 questions), (4) safety and first aid (SAFA, 10 questions), (5) medical care (MC, 11 questions), and (6) health information (HI, 6 questions). An overall health literacy score was computed as the sum of all three aspects and six dimensions.
Evaluation method
Four types of questions were included in the scale: true-or-false questions, single-answer questions, multiple-answer questions, and situation questions. For true-or-false questions and single-answer questions, 1 point was assigned to the correct answer. For multiple-answer questions, 2 points were assigned when all of the correct answers and no incorrect answers were chosen. For situation questions, the participants were required to answer single- or multiple-answer questions after reading the given material. A score of 0 points was recorded for a wrong answer. The overall health literacy score ranged from 0 to 66 points. The total points scored in the three aspects KAA, BAL, and HRS were 28, 22 and 16, respectively, and the total points scored in the six dimensions SVH, ID, CD, SAFA, MC, and HI were 11, 7, 12, 14, 14, and 8, respectively.
Variables
The participants were divided into 2 categories: (1) poor knowledge of health literacy (total health literacy score < 80% of the overall score, with a total score < 53 points) and (2) good knowledge of health literacy (total health literacy score ≥ 80% of the overall score, with a total score ≥ 53 points) [4, 24]. The knowledge rate (%) of health literacy was calculated using the following formula: total number of participants with good knowledge of health literacy / total number surveyed × 100%. The knowledge rates of the three aspects and six dimensions of health literacy were calculated similarly. Quality control was applied to the whole investigative process. Based on previous studies [25,26,27,28,29,30] and our results from the Chi-square test, the possible risk factors that may affect health literacy were chosen. The possible risk factors considered were the area of residence (0 = rural and 1 = urban), age in years (1 = 15–24, 2 = 25–34, 3 = 35–44, 4 = 45–54, 5 = 55–64, and 6 = 65–69), education (1 = illiterate, 2 = primary school, 3 = junior school, 4 = high school, 5 = college, and 6 = master’s degree or higher), occupation (1 = civil servant, 2 = teacher, 3 = medical staff, 4 = staff at other public institutions, 5 = student, 6 = farmer, 7 = worker, 8 = staff of other enterprises, and 9 = other), number of people in the household (1 = 1–3, 2 = 4–6, and 3 = ≥7), average annual household income (CNY) (1 = < 30,000, 2 = 30,000-50,000, 3 = 50,000-100,000, 4 = 100,000-300,000, and 5 = ≥300,000), suffering from chronic diseases (0 = no and 1 = yes), and self-reported health status (1 = excellent, 2 = good, 3 = average, 4 = relatively poor, and 5 = poor).
Statistical analysis
The data were meticulously sorted, cleaned, and analysed with SPSS version 21 (International Business Machines Corporation, Armonk, NY, USA). A descriptive analysis (frequencies, percentages, and means with standard deviations) of participant characteristics was performed. The Chi-square test was used to compare the knowledge rates of health literacy among subgroups. A multivariate logistic regression analysis was conducted to assess the associations of multiple potential risk factors with the knowledge rate of health literacy. The multivariate logistic regression analysis was used to adjust for the risk factors associated with health literacy. Statistical significance was defined as a p-value < 0.05 (two-sided).