Measurement and data collection
Version 1.0 of the SF-3623 was translated into Vietnamese by a professional translator and then translated back into English by another. No significant difference between the two translations was detected. The survey consisted of 36 questions related to eight health notions including physical functioning, role limitations due to physical health problems, role limitations due to emotional problems, energy/fatigue, emotional well-being, social functioning, bodily pain and general health perceptions, divided into two groups of physical and mental health.15 The responses were scored following the RAND scoring method.24 The 36-Item Health Survey 1.0 included the same set of items as the SF-36. In this research, we used the RAND 36-Item Health Survey scoring process consisting of 2 steps. Firstly, pre-coded numeric values were recoded according to the scoring scale described hereinafter. Responses 1 to 5 for items number 1, 2, 20, 22, 34, and 36 were recoded to values of 100, 75, 50, 25, and 0, respectively. Responses 1 to 3 for items number 3 to 12 were recoded to values of 0, 50, and 100, respectively. Responses 1 and 2 for items from 13 to 19 would be recoded to values of 0 and 100, respectively. Responses 1 to 6 for items number 21, 23, 26, 27, 30 were recoded to values of 100, 80, 60, 40, 20, and 0, respectively. Responses 1 to 6 for items number 24, 25, 28, 29, 31 were recoded to values of 0, 20, 40, 60, 80, and 100, respectively. Responses 1 to 5 for items number 32, 33, 35 were recoded to values of 0, 25, 50, 75, and 100, respectively. All the items were scored so that that a higher score indicates a better state of health-related QoL. In addition, each score of items ranged from 0 to 100, with 0 indicating the lowest and 100 the highest possible score. Scores are represented as percentage of the total possible score achieved.24 Secondly, items in the same scale were averaged together to create 8 sub-scale scores that yield eight health concepts. If the respondent missed one of the two items, the person’s score was set to be equal to that of the non-missing item.24
The high reliability of this scoring method for each of eight scales has been identified, with Cronbach’s alpha ranging from 0.78 to 0.93.24 The International QoL Assessment project has translated and validated the SF-36 for use in 45 countries.25 In this study, we also verified the suitability of the SF-36 based on our pilot study after translation and adaptation to the Vietnamese language and culture. The pilot research was conducted on 10 patients, and the results showed that all the scales were technically reliable and feasible for the main survey. In the main survey, the selected patients were interviewed face-to-face when they visited Vietnam Heart Institute (about 80% of the patients) or via telephone when any of them did not come at repeated surveys (20%).
The main predictor of interest is the QoL of patients across rounds (i.e., baseline, 1st and 3rd months of follow up)
Key selected characteristics. The demographic factors covered age (years), gender (male or female), educational level (lower level representing under or equal to high school or higher level including college or university and post-graduate level), marital status (single or married), occupation (retired or not retired/farmers), region (rural or urban), past coronary intervention before the current intervention (yes or no), hypertension (yes or not), hyperlipidaemia (yes or no), diabetes mellitus (yes or no), the number of stents inserted (1, 2, and 3 stents), smoking history (yes or no before the onset of UA), alcohol intake history (yes vs. no before the onset of UA), and troponin T (under or over 0,01 ng/ml).
Statistical analysis . The frequencies and percentages for categorical variables, and means and standard deviations (SD) for quantitative variables were used to describe the data. We calculated mean scores and standard deviations for eight subscales of the SF-36 at pre-intervention, one month, and three months after the intervention. In each of the eight subscales, higher scores indicated a better state of health-related QoL. As a repeated measures design, we used a mixed-effects model with random intercept to detect factors associated with QoL. Each individual had three observations, one at baseline, one at 1 month and the other at 3 months, with correlation assumed between observations within the same individual. All analyses were conducted using Stata version 16 (Stata Corporation, College Station, TX)
Research ethics . All subjects received verbal descriptions of the purpose and methods and their right to refuse participation at any time. They were reassured that their participation was voluntary and anonymous, and the refusal would not affect their treatment or nursing care. The protocol was approved by the Research Assessment Board from the Institute for Preventive Medicine and Public Health at Hanoi Medical University according to Decision No. 5403/QD-DHYHN dated 06/12/2016.