Study setting and subjects
We conducted a cross-sectional study from September 2019 to February 2020 among T2DM patients in Sarab city, East Azerbaijan Province, Iran. East Azerbaijan Province is situated in northwestern Iran and has mostly foothill and mountainous areas with an area of around 45,490 square kilometers. The province is bounded in the north by the Republic of Azerbaijan and Armenia. Sarab is located east of the province and sided the province of Ardabil. Its capital, Sarab city is 636 km. from Tehran, 130 km. from Tabriz to the east of Bostan Abad. This township resting amongst the high mountains of Bozqoosh and Sahand.
Based on the test exam from the t-test family, and from the “correlation: point biserial model” in the statistical test, using the G*Power software, the input parameters for two-tail hypothesis, effect size= 0.245, α error probability= 0.05, power (1- β error probability= 0.95), respectively, the sample size determined as 205 . Finally, 192 people agreed to participate in the study and all of them completed the written questionnaire (Response rate= 93.7%) to participate in the study.
Participants were recruited randomly from health centers by medical records among 6000 patients by using the command “=RANDBETWEEN(1,6000)” in the Excel software. The study sample was invited from amongst the people who met the study entry criteria. Subsequently, after referring to the healthcare centers and giving a complete explanation to the subjects and obtaining informed consent from them, they answered to the questionnaires in a consultation room. Besides filling the questionnaires, the participants interviewed by trained interviewers. The interviews lasted approximately for 25 minutes.
Inclusion criteria were diagnosis of T2DM in accordance with the final diagnosis instructions of the Iranian national laboratory standards, ≥30 years of age, with or without complications, lack of chronic illnesses and diabetes complications, and at least a six-month history of diabetes and having low education (secondary education and lower). The exclusion criteria were as follow: not having psychotic disorder, dementia, or blindness and refusal of participation and any medical problems that prevented self-care behaviors (such as exercise and regular physical activity) in the study.
Study instruments and their validity and reliability
The instruments for collecting data included: (1) demographics form; (2) health literacy questionnaire; (3) diabetes self-care behavior questionnaire; (4) WHO quality of Life-BREF (WHOQOL-BREF).
The demographics form consisted of gender (male, female), age (>50, 50 ≤), job (employed, unemployed, housewife), marital status (married or unmarried).
Health Literacy Questionnaire (HLQ)
To assess HL was used a valid and reliable tool which was established by Montazeri et al . A full explanation of the HLQ and its five subscales is described as follow:
1) Reading health information: the four-item subscale was evaluated on a five-point Likert-type scale ranging from 1 to 5 (1= completely difficult through 5=completely easy). An example of this aspect was: “reading health education materials (e.g., booklet, pamphlet, and educational brochures) was easy for me”. Cronbach’s alpha for this subscale was measured 0.72. The total possible scores varied from 4 to 20. The higher the score, the greater the reading abilities.
2) Understanding health information was assessed using seven items (e.g., “I can acquire the required health and medical information from various sources”). Each item was scored on a 5-point scale from 1 to 5 (1= completely difficult through 5=completely easy). For this subscale, Cronbach’s alpha was 0.86. The theoretical range for this subscale was 7–35 and the higher the ratings, the more comprehensible to understand health information.
3) Appraisal of health information was assessed applying four items. (e.g., “I can get information about healthy nutrition”). Each item was scored on a five-point Likert-type scale that ranged from 1 (never) to 5 (always). Cronbach’s alpha for this subscale was 0.77. The total score on this subscale could range from 4 to 20. A high total score shows a high ability of appraisal of health information.
4) Ability to access health information was measured by six items (e.g., “I can obtain information about my illness”). A five-point Likert-type scale was used (always= 5, most of the time= 4, sometimes= 3, seldom= 2 and never= 1). Cronbach’s alpha for this subscale was 0.86. The total possible scores ranged from 6 to 30, higher the score, the more ability to access health information.
5) Decision making was a twelve-item subscale designed to measure the ability to decide health-related behaviors. Sample of items is: “I avoid doing things or taking materials that might increase my weight” even if the symptoms of the disease would be disappeared. The items were scored on a five-point Likert-type scale ranging from 1 to 5 (always= 5, most of the time= 4, sometimes= 3, seldom= 2 and never= 1). For this subscale, Cronbach’s alpha was 0.89. The higher the ranking, the better decision making was concluded.
Diabetes Self-care Behavior Questionnaire
We used a 12-item summary of diabetes self-care activities scale,  to measure self-care performances. This questionnaire had been validated by Didarloo et al., among people with type 2 diabetes in Iran . The Cronbach’s alpha was assessed 0.74. The scale measures frequency of self-care behaviors in the last 7 days in four dimensions of the diet (6 items), glucose testing (2 items), medications (2 items) and physical activity (2 items). The total self-care activities score on this index may range from 0 to 84 in which higher scores indicate higher self-care behaviors adopted by the patients.
WHO Quality of Life-BREF (WHOQOL-BREF) Questionnaire
A standardized Persian version of the WHO’s questionnaire (WHOQOL-BREF) was applied to assess HRQL among participants. Validity and reliability of this translation of WHOQOL-BREF was approved in a study conducted by Nejat et al.  in Iran. This instrument includes four domains: physical health (7 items; α= 0.70), mental health (6 items; α= 0.73), social relationships (3 items; α= 0.55), and environmental health (8 items; α= 0.84). The items were rated on a five-item Likert scale ranged from 1 to 5 for all the domains. The scoring of the answers to items 3, 4 and 26 has been reversed. A score of 0 to 100 has been obtained after performing the calculations at each domain. The ranking of 0 shows the poorest quality of life and the best condition calculated as 100. Such values can also be translated to a ranking of 4 to 20 . In this study the scores range from 0 to 100 in each dimension.
For the categorical variables, percentages and frequencies applied while for the continuous variables, the mean and standard deviation or median and quartile deviation, depending on the distribution of the data. All analyses were conducted using SPSS 21.
Bivariate comparisons were performed using the independent samples T-test for quantitative variables. Pearson Correlation are used in to measure a relationship is between between HL and self-care with HRQL. Pearson's r can range from -1 to 1.
Hierarchical regression analysis for HRQL was carried out by entering 3 separate blocks of independent variables. Block 1 consisted of age, gender, job, marital status which were operationally defined as the demographic characteristics and were entered first. Block 2 included HL dimensions. Block 3 was consisted of the scores from demographic characteristics, HL, self-care behaviors. After the entry of each block, we measured the adjusted R2 change to decide the proportion of variance described by HRQL. Tests for multi-colinearity, normality, and influential data points demonstrated that the assumptions of regressions were met. The significance level was set to α= 0.05.