Vietnam’s life expectancy at birth has been increasing significantly in recent decades , yet simultaneously so has the prevalence of chronic illnesses . For instance, the prevalence of people with hypertension among the general population aged 25–64 years was reported to increase from 15.3–20.3% in 2010 and 2015, respectively . The characteristics of people living with such diseases varied among living conditions, sex, and economic status, which were clearly shown in the 2015 national survey on non-communicable disease factors . Vietnam’s Ministry of Health (MOH) is upgrading the healthcare system to provide sufficient healthcare services for people living with long-term illnesses . The MOH has enacted several targeted programmes to prevent non-communicable diseases; nevertheless, efficient measures to monitor and evaluate these programmes are still in need . Intermediate outcomes (e.g. levels of systolic and diastolic blood pressure) and natural measures (e.g. number of deaths / or averted cases) are sometimes not adequate enough to evaluate the effectiveness of a healthcare intervention for people living with chronic illness . For example, health interventions on hypertension may simultaneously exert effects on people with cardiovascular diseases . Hence, multi-dimensional health outcomes are needed to identify the additional health benefits offered by such interventions . A multi-dimensional health outcome, the health-related quality of life (HRQOL), is now getting more attention [6, 9]. The HRQOL, which has been commonly used to investigate the impact of health status on quality of life [10–12], can be described by many different health dimensions and at different levels achieved within each dimension . Several measurement instruments attempt to describe HRQOL, but overall, it can be grouped into either disease specific measures – designed to measure the HRQOL of people with some specific health problems (e.g. EORTC QLC-C30 or EORTC-8D for cancer patients); or generic measures to describe HRQOL of any health status that can be represented by different health dimensions with their respective levels of achievement/severity (e.g. a profile-based measure: 36-Item Short Form Survey - SF-36; index-based measures: EQ-5D, SF-6D, Health Utility Index - HUI) . The disease specific measures are customised according to disease’ characteristics, whereas the generic measures are responsive to overall HRQOL, and are more flexible in their use for comparisons across disease areas . Therefore, utilising a generic measure for HRQOL estimations support consistent policy-making processes, and enable comparisons between the amount of health gained and lost within society .
Vietnam’s MOH has taken the first steps in making use of a generic measure for HRQOL in healthcare service’s evaluations by enacting the national health technology assessment (HTA) guidelines and upgrading the health insurance benefit package with cost-effective drugs based on HTA evidence . Those facts implied a demand to promote evidence-informed policymaking in the national healthcare system, initially in health insurance. According to the national guideline on HTA submissions, the measure of generic quality adjusted life years (QALY) is a suggested index in Vietnam. Health outcomes as HRQOL and/or QALY have also been requested by other countries when it comes to HTA [14–17].
The number of QALY(s) can be estimated by multiplying the number of years of life with the quality of life during those years . Whilst years of life is an obvious indicator, quality of life can be represented by a generic index-based measure of HRQOL, under the term “utility”. This utility conventionally runs on a scale from 0 - representing “death” to 1 – which is “full health”. Several discussions on negative value of utility (for worse than death states of health) still generate controversy [8, 9]. Utilities are commonly measured by three instruments to quantify HRQOL, including EQ-5D; SF-6D, and HUI . In Vietnam, EQ-5D-5L is currently the only instrument that can produce utility that is based on preferences of the general Vietnamese population . Therefore, EQ-5D-5L has been suggested in the Vietnam’s HTA guidelines. The EQ-5D-5L instrument includes five dimensional five-level questions, a visual analogue scale (EQ-VAS), and a value set which was tailored for the Vietnamese people . The application of EQ-5D-5L can be included but not limited in QALY estimations. The instrument itself can reflect people’s quality of life via their health status being reported by either the five dimension five-level questions, or the EQ VAS scores, or the health state’ values.
The EQ-5D-5L has already been suggested in the national HTA guidelines, yet there are still two big concerns regarding the instrument. The first one is that Vietnam needs reference data allowing utility comparisons between people with certain health conditions and the general population of the same age/gender. The reference data deriving from EQ-5D-5L is one of such utility reference data, and it is also referred to the name as “EQ-5D-5L population norm data” or “EQ-5D-5L population norms” . The EQ-5D-5L population norms typically provide three outcomes, including the reference data of descriptive five dimensional five levels, EQ-VAS, and EQ-5D indexes. The EQ-5D-5L descriptive refence data is presented in percentages of the general population at each of five levels (from “no problems” to “unable to do/extreme problems”) on each of five health-related dimensions. The EQ-VAS reference data can often yield a table of mean(s)/median(s) EQ-VAS scores by age-sex groups, while the mean(s)/median(s) EQ-5D-5L indexes were derived from the national value set for the EQ-5D-5L indexes reference data . The population norms using the EQ-5D-5L were developed globally, from Western countries [21–30] to Asian countries [31–37]. A hint of population norms using the EQ-5D-5L for the Vietnamese has been done elsewhere, but the study included an urban population only, and furthermore, used Thai preferences . Since Vietnam has now had a country-specific value set, this is timely to develop the country-specific EQ-5D-5L population norms.
The second concern is whether EQ-5D-5L can be justified for use in Vietnam. Psychometric properties of the EQ-5D-5L have been proven in several countries and for several disease areas [38–48]. The instrument’s reliability, which concerns stability in measuring people’s quality of life, can often be proven by the consistency of HRQOL results obtained through different measurement instruments [38–43], and/or by the repeatability by each time using the instrument [44–46]. Validation of the EQ-5D-5L was also tested via different construction validations, commonly including convergent and known-groups validation. The convergent validation was for strong correlations between postulated dimensions and other dimensions that should, in theory, be considered relevant . Thus, correlations of the five dimensions (mobility, usual activities, self-care, pain/discomfort, and anxiety/depression) with other respective dimensions of other different instrument(s) are often evaluated for convergent validation purposes [46–48]. Meanwhile, the known-groups validation to evaluate the sensitiveness of the instrument is expected to yield distinctive results among different groups of patients [44, 47]. A study on the reliability and convergent validation of the EQ-5D-5L in Vietnam was conducted among HIV/AIDS patients , yet the construct validation among people with chronic diseases is still limited. To fill the research gaps, this study aims to provide (1) HRQOL reference data using EQ-5D-5L among the general population and (2) validity tests for the EQ-5D-5L instrument among people living with hypertension in Vietnam.