3. Research problem and aims of my PhD
2022-06-08
0.1 3.1. Conceptual framework
In Chapter 1 of this thesis, I described the concept of the social determinants of health (SDH), along with the relevance of hypertension worldwide and in Chile. In Chapter 2, I evaluated the available evidence on SEP inequalities in hypertension management in LACCs. In this short chapter, I include three main hypertension-related outcomes (Figure 3.1 below) to the PAHO’s adaptation of the WHO’s conceptual framework on the SDH that was set out earlier (Figure 1.1, Chapter 1). This conceptual model helped to formulate the research problems, aims, objectives and hypotheses that informed the following four empirical chapters.
Figure 3.1: Conceptual model of the study
The framework distinguishes between three main outcomes: (i) hypertension prevalence, (ii) the three key (care cascade) steps in the pathway for the management of hypertension (diagnosed, treated and controlled hypertension), and (iii) mortality. Mortality was included in the conceptual framework, since indicators of SEP, hypertension as a condition (chronic disease), and having diagnosed-, treated- and controlled-hypertension have separately been associated with mortality.[1, 2]I decided to place these three main hypertension-related outcomes in separate boxes because those factors potentially associated with SEP inequalities in hypertension management may differ from those related to SEP inequalities in hypertension and from those associated with the risk of all-cause and cardiovascular mortality.
The framework distinguishes between individual and contextual factors. Individual factors include the individual-level SEP indicators covered in the systematic review of inequalities in hypertension management in LACCs (education, income, occupation) but also includes those particularly relevant to the Chilean context (i.e. health insurance). Contextual factors, including socioeconomic environment measures (e.g. those summarising the socioeconomic level of a region or county), are also included to capture factors that potentially influence inequalities in each hypertension related outcome over and above those accounted for by individual-level SEP factors. The framework sets the scene for the four empirical chapters of my PhD by illustrating the importance of statistically controlling and quantifying the impact of potential confounders or moderators (e.g. survey year, age, gender) on the magnitude and direction of SEP-inequalities in these outcomes.
0.2 3.2. Research problems
More specifically, the four research problems outlined below will be the focus of the empirical chapters:
Recent evidence on hypertension prevalence and management in Chile was based on analysis of data from the health surveys conducted in 2003 and 2010. Therefore, more up-to-date research using data from the most recent ENS 2017 is needed to update evidence on the hypertension-related outcomes and to evaluate if the most recent secular changes are similar or different to those observed comparing 2003 and 2010.
Chilean evidence has shown SEP inequalities in hypertension prevalence.[66] However, information on SEP inequalities at the steps of the hypertension care cascade (diagnosis, treatment and control) in Chilean adults is only partially known.
There is an information gap on the impact of contextual SEP factors on individual level SEP inequalities in hypertension and in diagnosed, treated and controlled hypertension in Chilean adults.
There is currently no information available on differences in all-cause and cardiovascular mortality rates among Chilean adults by hypertension status or by educational level. ENS survey data linked with mortality data were recently released by the Chilean Ministry of Health. To the best of my knowledge, no research has been published using these cohort data.
0.3 3.3. Aims
Related to these research problems, the overarching aim of my thesis is to:
Examine socioeconomic inequalities in hypertension prevalence and at each care cascade step (undiagnosed, untreated and uncontrolled hypertension) in Chile.
The aims of the following four empirical chapters are:
To quantify gender-specific trends in hypertension prevalence and in attainment of the indicators of awareness, treatment, and control. I also aim to quantify the impact of lowering BP thresholds on these hypertension outcomes (Chapter 4).
To examine the magnitude of SEP inequalities in hypertension prevalence and in its three key management indicators (undiagnosed, untreated and uncontrolled hypertension), and their changes over time in Chilean adults, using individual-level measures of SEP (Chapter 5).
To examine individual-level educational-based inequalities in hypertension and in undiagnosed, untreated and uncontrolled hypertension in Chilean adults in 2003, 2010 and 2017 taking into consideration contextual SEP measures by using a multilevel analytical approach (Chapter 6).
To evaluate associations between (i) hypertension status, and (ii) individual-level educational status, and all-cause and cardiovascular mortality using ENS-mortality linked data (Chapter 7).
The specific objectives and hypotheses for each aim are stated within the relevant chapter.
0.4 3.4. Ethics approval and consent to participate
The Ethics Committee of the Pontificia Universidad Católica de Chile (PUC) approved the study protocol for this PhD (IDs: 200205003 and 211116004, certificates provided in Appendices 4 and 7). The PUC ethics committee and the Chilean Ministry of Health approved the Chilean National Health Survey (ENS) study protocol and ethical consent forms (ENS2003: number not retrieved; ENS2010 ID: 09-113; ENS2017 ID: 16-019). Persons selected for inclusion in the Chilean health surveys provided informed and signed consent before participation.