Mapping the concept of vulnerability related to health care disparities: a scoping review

Health care disparities are well studied and documented problems that generally refer to differences in the quality of health care - in terms of access, treatment options, prevention and health outcomes - across groups that reflect social inequalities [1‐6]. Segments of the population at risk of poor health and health care disparities are usually considered as being vulnerable [7, 8]. The concept of vulnerability has become increasingly popular in the scientific literature over the last decades. Rooted in a large array of disciplines such as economics, sociology, anthropology, environmental science and health, these papers refer to various definitions and measures of vulnerability [9]. In regard to the health literature specifically, most of the papers use the concept of vulnerability to indicate the potential risk of developing certain diseases or suffering from environmental hazards. Nevertheless, there is also a fairly large number of publications devoted exclusively to the study of vulnerable populations. These publications have generally introduced and debated conceptual models as frameworks for studying the origin and the consequences of vulnerability on poor health [8, 10]. Although these papers sometimes suggest that people who are at risk of poor health are also more likely to face health care disparities, they do not usually focus on studying those disparities. They also do not explicitly examine the link between health care disparities and the co-existence of multiple aspects of vulnerability. Thus, given the broad scope and rapidly growing scientific evidence, we argue that there is a need for a critical review of the literature aiming to grasp the strengths and weaknesses of the current state of knowledge.

The aim of the present review was to examine the concept of vulnerability in connection with the health care disparities faced by distinct subpopulations generally viewed as vulnerable. Furthermore, our main purpose was to determine what is known, from the existing literature, about the relationship between health care disparities and the multiplicity of risk factors that are often clustered together and acting synergistically in the same individual.

To reach these objectives, we used the scoping review as an investigative method. The scoping review originated in the work of Arksey and O’Malley from the Centre for Reviews and Dissemination at the University of York [11] and is becoming an increasingly popular method of reviewing health research evidence. Scoping reviews are used to methodically describe the size and nature of the evidence base for a particular topic area, which can in turn be used to identify gaps in the literature and make recommendations for future primary research [11‐15]. Scoping reviews generally differ from systematic reviews: (1) by addressing broader and more heterogeneous questions; (2) by including studies of many different methodological designs; and (3) by not necessarily assessing the quality of the included studies [11‐13, 15, 16]. Thus, the advantages of a scoping review lie in its flexibility and creativity, since it aims to give meaning to the “what” and “why” as opposed to the “who”, “where” and “how” that are specific to the systematic review [14]. The scoping review was our method of choice mainly because, given the exploratory nature of our research question, it was not possible for us to exclude heterogeneous evidence (e.g. qualitative, non-research) whose quality could not be easily appraised by the traditional methods used for systematic reviews.

This scoping review is premised on the phenomenon termed the Inverse Care Law (ICL) [17, 18], which states that the people with the greatest health care needs receive the least health care services. There is a growing body of research evidence indicating that the socioeconomically deprived are less likely to have a regular physician and more likely to report difficulties obtaining needed primary, secondary and/or preventive care [19, 20]. Although this unfortunate paradox of the availability of good medical care, which tends to vary inversely with the need for it, has already been well studied and documented [19], there is still little research on how the ICL operates. Moreover, few studies have examined the combined influence of multiple risk factors on obtaining needed health care services [21].

Based on the evidence-based phenomenon of the ICL, we propose a conceptual model of multi-vulnerability that illustrates the dynamic relationship between health care services received, needs, and level of vulnerability (Figure 1).

The model is a right-angled triangle whose base (horizontal cathetus) represents the continuum of health care accessibility and quality, which can vary from low to high. The vertical cathetus represents the continuum of health care needs, which also vary from low to high depending on the number of vulnerability factors that co-exist in the same individual at a given moment. The triangle’s hypotenuse corresponds to the level of vulnerability that tends to vary directly with health care needs and inversely with accessibility and quality of care. For instance, an individual (A) would experience high vulnerability because of the co-existence of multiple vulnerability aspects, which would result in higher health care needs and be associated, according to the ICL, with lower health care accessibility and quality. Conversely, an individual (B) would experience low vulnerability if he/she presented fewer vulnerability aspects and, therefore, would have low health care needs associated with higher accessibility and quality of health care.

Even though the ICL was originally used to explain inequalities in health care faced by the socioeconomically deprived, we hypothesize that other vulnerability aspects would be subject to the same phenomenon. Moreover, an increase in co-existing vulnerability factors would also be correlated with an increase in health care disparities.

We operationalize vulnerability as an increased susceptibility to health and health care disparities due to a combination of individual and environmental factors. The individual characteristics can be either inborn (e.g., gender, race, genetic predispositions to disease) or acquired (e.g. trauma, diseases, lifestyle), while the environmental aspects refer either to the immediate physical environment (e.g., temperature, pollution, housing, community and neighborhood characteristics) or to the broader socioeconomic environment (e.g., social networks, historical, political, and cultural context) [7, 8, 22, 23]. Our conceptualization of vulnerability is also inspired by the community social resources model by Flaskerud and Winslow, which suggests that vulnerability stems from a lack of socioeconomic and environmental resources. The socioeconomic resources refer to human capital (i.e. income, jobs, education and housing), social connectedness and social status. The environmental resources are operationalized as access and quality of health care and concern the characteristics of the community and the availability of health care professionals and social service providers [24].

This study’s method was based on the scoping review framework outlined by Arskey and O’Malley [11] and encompasses five stages: identifying the search question, identifying the relevant studies, selecting the studies, charting the data, and summarizing and reporting the results.

The goal of this paper was to present the results of a scoping review on the concept of vulnerability in connection with health care disparities. Moreover, we intended to identify what is known, in the existing literature, about the relationship between health care disparities and the co-existence of multiple aspects of vulnerability. The main finding of this scoping review is that the body of literature on vulnerability in health care research confirms the framework of our dynamic vulnerability model of health care disparities based on the ICL. Thus, the results suggest that high levels of vulnerability (due to the co-existence of multiple vulnerability aspects) would increase health care needs and would be associated to lower health care accessibility and quality. These findings are consistent with other research showing that the ICL phenomenon holds even under universal health insurance systems such as the UK and Canada, and it holds with greater force in countries without universal health insurance [18, 19, 27, 49]. However, the total number of studies that operationalized vulnerability as a combination of factors is too small for drawing statistically firm conclusions regarding the relationship between the increase of co-existing vulnerability factors and the escalation of health care disparities. Hence, there is a need for more research into the scientific validation of this correlation. Moreover, we recognize the need for studies to identify the clusters of vulnerability aspects that increase the probability of facing health care disparities. This research will provide the policy-making process with currently missing information on how the ICL actually operates and will eventually help reduce inequalities in health and health care.

Our review revealed that despite its substantial additions, the existing literature has both important theoretical and empirical limitations. For instance, the vast majority of papers is mostly heuristic and lacks a solid theoretical basis. Even when based on a conceptual framework, the one that prevails is the initial behavioral model of health services use [46] that was often criticized and repeatedly revised to emphasize the dynamic and recursive nature of health care use [45, 50]. The reviewed research studies also have some important methodological limitations related mostly to their reliance on survey data, which could preclude causal interpretation and only measure statistical associations and tendencies.

Our review also revealed that there is currently little research concerned with the health care disparities related to the co-existence of multiple aspects of vulnerability. Of the 759 references generated by the initial search, only 23 referred, explicitly or implicitly, both to health care disparities and to the co-existence of two or more aspects of vulnerability. Moreover, less than half of these reviewed publications provided empirical evidence on the relationship between health care disparities and the co-existence of multiple vulnerability factors. When taken into consideration, this connection referred mostly to demographics and social structure, ignoring health beliefs and patients’ experience of illness. According to several authors, health and illness beliefs are of great importance in explaining the use of medical and preventive services, as they directly affect need and, consequently, services use [45, 51, 52].

The fact that none of the included papers addressed the beliefs or conceptions about health and illness of vulnerable populations is, in our opinion, the major gap in the reviewed literature. In fact, all the reviewed publications approached vulnerability from a normative perspective based on socio-demographic characteristics that assign certain populations a higher probability of health or health care disparities. Spiers [53] contrasts this kind of approach, which she names “etic”, with an “emic” perspective on vulnerability. Inspired by the anthropological literature, the emic approach to vulnerability refers to a description of the phenomena as perceived by the concerned person and reflects the lived experience of “vulnerable” populations. According to the author, research on vulnerability would greatly benefit from the integration of the emic dimension to the etic approaches to vulnerability, as this combined perspective would provide a more satisfactory picture of how people manage multiple challenges in their daily lives [53].

The present review also revealed a series of additional gaps in the literature that could be interpreted as opportunities for future research. These gaps pertain to location and type of studies, and the aspects of vulnerability related to health care disparities. Regarding location, the vast majority of the publications were conducted in the United States, where there is no universal health care system to sustain appropriate care for vulnerable populations. However, there is evidence that health care disparities on the basis of poverty, race and immigrant status persist even in countries with a universal health care system [54]. Therefore, we argue that future research conducted in countries with a publicly funded health care system (e.g., Canada, the UK) would increase our understanding and, eventually, contribute to the reduction of these disparities.

In regard to the types of studies, no qualitative research satisfied the inclusion criteria of our scoping review. Besides the discussion papers that addressed vulnerability and health care disparities from a theoretical perspective, the research papers exclusively reported findings from quantitative studies. Even though these studies might present the usual strengths of quantitative research (e.g., structured research design, generalization of findings, statistical significance, and objectivity of the researcher), they also have weaknesses. Without entering into a debate over the advantages and disadvantages of both types of research, we argue that studies on health care disparities related to vulnerability could only benefit from the integration of more flexible qualitative techniques in their design.

Concerning the aspects of vulnerability involved in health care disparities - with respect to the community social resources model [24] - our review has shown that the vast majority of papers focused on the lack of socioeconomic resources; namely, human capital (i.e., poverty, low level of education, unemployment, and homelessness) and social connectedness (i.e., racial/ethnic minority, old age, immigrant status, and widowed status). Only a few studies took into consideration the aspects related to environmental resources (i.e., residence in underserved areas) and none of them referred to the vulnerability to hazards and disaster events (see Table 3). Since the likelihood of a hazard event combined with the lack of socioeconomic resources results in higher degrees of vulnerability and increased needs of people living in certain communities [55‐57], we recognize the need for research that examines the link between this “vulnerability of places” [55] and health care disparities.

Our review also revealed a paucity of studies envisaging the close connection between chronic illness and health care disparities, even though it has already been suggested that people living with chronic conditions may experience challenges when navigating through the health care system [58‐60]. Moreover, the co-existence of two or more chronic diseases in the same person (i.e., multimorbidity) as a vulnerability aspect was almost absent from the publications reviewed.

The prevalence of multiple chronic conditions in the same individual has dramatically increased over the past years and is starting to be recognized as a critical clinical issue in health care, mostly because of its negative effects on patient quality of life, mortality, and treatment complications [61‐63]. Several studies also found that individuals with multimorbidity have trouble obtaining quality care, usually in terms of access and coordination [64, 65]. However, research on multimorbidity is still in its infancy [66] and our scoping review revealed that there are very few studies considering multimorbidity as a vulnerability factor in connection with health care disparities. Further research addressing health care disparities related to multimorbidity that co-exists with other vulnerability factors (e.g., poverty, belonging to an ethnic minority, etc.) might lead to crucial information on how to transform typical primary care practices to meet the needs of the most vulnerable patients.

Another vulnerability aspect that has received little attention in the research literature is immigrant status. Even though a large majority of the papers considered racial/ethnic minority as a vulnerability factor, health care disparities experienced by immigrants involve more complex interrelated issues because of other vulnerability aspects than ethnicity. Thus, several studies found that even within the same racial/ethnic group, immigrants received significantly less medical and preventive care than their non-immigrant counterparts [67‐69]. Among the potential reasons that account for these findings are: language and cultural barriers [70, 71], disparities in health care insurance [72], and a lack of familiarity with the local health care system [73].

The above-mentioned problems are frequently combined with chronic poverty, especially for recent immigrants [74, 75], and with an increase in the prevalence of chronic diseases [76, 77]. All these aspects lead naturally to the conclusion that immigrant status is an important vulnerability aspect that often co-exists and may synergistically interact with other recognized factors involved in health care disparities. We consider that further research addressing these interactions would be beneficial for finding solutions aimed to overcome such disparities.

Before concluding, it is important to raise some limitations of our scoping review. First, we restricted the search strategy to databases that usually cover the health, public health and psychological literature (i.e. MEDLINE-Ovid, CINAHL, EMBASE and PsycINFO). For practical reasons, we were unable to exhaustively search the social sciences databases and to include papers in a language other than English or French. Therefore the risk that not all relevant studies were identified remains. Second, we located and analyzed only 23 publications on the topic, which precludes a comprehensive assessment of such a complex domain. These 23 papers tended to be rather diverse in both their focus and design, which led us to make decisions regarding the information to be summarized and analyzed. Furthermore, since scoping reviews do not typically include a quality assessment of included studies, data synthesis and interpretation could be limited [78, 79] and the evidence to base decisions regarding the need for future research could be insufficient [15]. However, we are confident that our scoping review provided original data with a richness and fineness that would have been difficult to attain with other types of literature reviews.

This scoping review confirmed our hypothesis of the direct correlation between the increase of co-existing vulnerability factors and the escalation of health care disparities. However, it also revealed that there is currently little research concerning health care disparities related to the co-existence of multiple aspects of vulnerability. Several gaps in the literature were identified, among which the most important seem to be a lack of research focusing on vulnerable populations’ perception of their own vulnerability, and on multimorbidity and immigrant status as aspects of vulnerability.

We argue that future research addressing these gaps would help foster primary care interventions that are responsive to the needs of vulnerable people and, eventually, contribute to the reduction of health care disparities in society.