Measuring Health Equity in Emergency Care Using Routinely Collected Data: A Systematic Review

Introduction: Achieving equity in health care remains a challenge for health care systems worldwide and marked inequities in access and quality of care persist. Identifying health care equity indicators is an important first step in integrating the concept of equity into assessments of health care system performance, particularly in emergency care. Methods: We conducted a systematic review of administrative data-derived health care equity indicators and their association with socioeconomic determinants of health (SEDH) in emergency care settings. Following PRISMA-Equity reporting guidelines, Ovid MEDLINE, EMBASE, PubMed, and Web of Science were searched for relevant studies. The outcomes of interest were indicators of health care equity and the associated SEDH they examine. Results: Among 29 studies identified, 14 equity indicators were identified and grouped into four categories that reflect the patient emergency care pathway. Total emergency department (ED) visits and ambulatory care-sensitive condition-related ED visits were the two most frequently used equity indicators. The studies analyzed equity based on seven SEDH: social deprivation, income, education level, social class, insurance coverage, health literacy, and financial and nonfinancial barriers. Despite some conflicting results, all identified SEDH are associated with inequalities in access to and use of emergency care. Conclusion: The use of administrative data-derived indicators in combination with identified SEDH could improve the measurement of health care equity in emergency care settings across health care systems worldwide. Using a combination of indicators is likely to lead to a more comprehensive, well-rounded measurement of health care equity than using any one indicator in isolation. Although studies analyzed focused on emergency care settings, it seems possible to extrapolate these indicators to measure equity in other areas of the health care system. Further studies elucidating root causes of health inequities in and outside the health care system are needed.

However, achieving equity in health care remains a challenge for health care systems worldwide.(5)(6)(7) Several recent studies raise the importance of addressing the concept of equity when making decisions about health care policies and practices.(8-10)However, the performance assessment of health care systems has traditionally been limited to quality and e ciency indicators and health care decision makers remain poorly informed about equity,(8) particularly in some speci c settings, such as emergency care.(10) Measuring and monitoring equity is therefore an emerging area of interest in assessing emergency care performance.(10)(11)(12)(13) Emergency care is a unique health care setting as it is situated at the interface of outpatient (ambulatory) care and inpatient (hospital-based) care.Identifying indicators of health care equity in this setting make it possible to assess both access to outpatient care while also highlighting differences in quality of care within hospital-based care.(14,15) To ensure accessibility of quality data on relevant variables for measuring health care equity, several approaches and data could be used, from primary qualitative or quantitative data to the use of routinely collected administrative data.For this study, we have decided to focus on studies based upon routinely collected administrative data as it has two fundamental advantages in the analysis of health care equity: the achievement of near complete coverage of the target population and the possibility of disaggregation in subpopulations.Moreover, using administrative data minimizes cost and burden of response.(16) Finally, for the purposes of this review, we have focused our analysis on studies measuring equity through socio-economic determinants of health (SEDH), i.e. the level of education, nancial resources, social and material living conditions.(17,18) The aim of this systematic review is to identify how health care equity is measured through the combination of administrative data-derived emergency care equity indicators and SEDH with the goal of creating a set of valuable and replicable indicators that can be used in the identi cation and analysis of health care equity in emergency care settings.

Ii. Methods
The protocol of this systematic review was published in PROPSPERO at the outset of the study.(See Additional le 1) The reporting of this systematic review was based on the PRISMA-equity guidelines.(19) (See Additional le 2)

A. Inclusion/Exclusion Criteria
We included studies reporting on health care equity indicators, and that were analysed as such, with a focus on studies that used administrative data and were conducted in emergency care settings in highincome countries.As the objective of this systematic review is to focus on health care equity in the context of emergency care and not to identify inequalities in emergency care provision between countries, a focus was placed on studies conducted in high-income countries.It is indeed di cult, in countries where health care resources are often lacking or insu cient, to determine whether variations in the use of care amongst certain populations are linked to inequities in access to care or whether they are the result of an overall lack of resources in the health care system.We included studies on adults (age 18 and over).If a study included both children and adults, we limited data extraction to data pertaining only to adults.We included studies regardless of whether or not a disease-speci c focus was taken (for example cancer, chronic diseases or mental health).Searches were limited to articles in English, German, French, and Italian (due to the language skills of the authors) published between January 2010 and January 2019.We chose to focus on studies published after 2010 because of the signi cant evolution of health care equity-related literature that followed the WHO Report "Closing the gap in a generation: Health equity through action on the social determinants of health".(20) We limited our analysis to studies looking at inequities and their associated SEDH as de ned above, excluding studies looking at determinants of health such as race/ethnicity, gender or place of residence, in order to ensure consistency and comparability between studies and countries.(4)(18) We excluded studies that did not focus on equity, as well as opinion papers, editorials, conference abstracts and study protocols.

B. Search Strategy
The search strategy was conducted with the assistance of a medical librarian using four 4 databases: Ovid MEDLINE, EMBASE, PubMed and Web of Science.We used keywords in the eld of equity, socioeconomic factors and emergency care.We combined the Medical Subject Headings (MeSH) terms "Health Services Accessibility", "Health Equity" or "Health care Disparities" with a combination of terms de ning administrative data and with text words "emergency department" or "emergencies".Initial searches were conducted in November 2018 to assess the scope of the literature.The nal search was conducted in January 2019.The full search strategy can be found in supplementary le 3. (See Additional le 3) Following the initial search, to identify any further relevant studies that were not initially captured or had not yet been published, we screened reference lists of all included studies and performed Google and Google Scholar searches using key search terms.

C. Study Selection
Two reviewers (KM, XL) conducted screening of articles independently and in duplicate.This was done in two stages.First by screening all titles and abstracts and second, by reviewing the full-text of all relevant articles to determine their eligibility in the nal analysis.Two other reviewers (JM, PB) provided arbitration in the event of a disagreement at both stages of screening.Reasons for exclusion of articles at the fulltext screening stage were documented.

D. Data Extraction
Two authors (KM, XL) extracted data independently and in duplicate from included studies using Rayyan ® (free online systematic review management system) and any discrepancies were resolved by consulting the two other reviewers (JM, PB).Data on the key characteristics of the studies were extracted in a prede ned data extraction form, into an Excel ® spreadsheet, including information about the design of the study, population, type of data, indicators of health care equity, SDEH addressed, main ndings and key conclusions.

E. Quality and Bias Assessment
In the absence of international consensus on a validated tool for the analysis of the risk of bias in observational studies, we based our analysis on the ROBINS-E tool (Risk Of Bias In Non-Randomized Studies -of Exposure) derived from the validated ROBINS-I tool (Risk of Bias In Non-Randomized Studies -of Interventions).(21) Through a comprehensive analysis of the methodology applied in each study, this tool helps identify the main intra-and inter-study biases amongst included studies.

F. Conceptual framework for the analysis
To address equity, we based our analysis on a conceptual framework of access to health care, developed by Levesque and al.(22)This framework combines ve dimensions of accessibility (approachability, acceptability, availability/accommodation, and affordability/appropriateness) with ve corresponding abilities of the target population (ability to perceive, to seek, to reach, to pay and to engage).It provides a comprehensive approach to health care equity and the different factors that could impact it.(Figure 1) We will use this framework to structure data extraction.

Iii. Results
The initial search yielded 354 papers of which 29 were included in the nal analysis.(Figure 2) Of these, 17 (59%) were conducted in the United States (US), 5 (17%) in the United Kingdom (UK), 3 (10%) in Canada, 2 (7%) in Australia, 1 (3%) in Sweden and 1 (3%) in Switzerland.Twenty-eight (97%) were written in English and one (3%) in French.A summary description of each study is presented in Additional le 4.

Equity indicators
The analysis of the 29 articles highlighted 14 different indicators used to assess health care equity.We categorized them into four groups according to the part of the patient care pathway they analysed, inspired by the "5 ve dimensions of accessibility" de ned in the framework of Levesque et  This group of indicators analysed access to outpatient care through differences in emergency care consumption (poor access to outpatient care leading to excess emergency care use).Therefore, they are indirect indicators of access to outpatient care.Five indicators belonged to this group.
(1) ED visits/Emergency admissions [1] rate With 26% (n=7) of articles using this indicator, it was the most commonly reported indicator identi ed in this systematic review.(23)(24)(25)(26)(27)(28)(29) It was used to highlight disparities of access to outpatient care.Since both re ect poor access to quality primary care, we have grouped them under the same indicator.
(2) Ambulatory care sensitive conditions (ACSCs) [2] ED visits/ACSCs emergency admissions rate Also called Preventable ED visits/Preventable emergency admissions, this indicator, used in seven articles, is used as often as the previous indicator "ED visits/Emergency admissions rate".(10,24,26,(30)(31)(32)(33) It is deemed a more speci c indicator than "ED visits/Emergency admissions" alone to assess disparities in access to outpatient care.The second group of health care equity indicators identi ed was indicators of quality of emergency care.They characterize disparities of care in the ED among targeted SEDH.
(5) Emergency speci c procedures rate Emergency speci c procedures comprised a combination of different procedures performed during emergency care, highlighting disparities in the quality or access to care for speci c emergency conditions such as a brain scan for the diagnosis of acute stroke,(36) reperfusion therapy in acute stroke, (37) and cardiac catheterization after myocardial infarction or cardiac arrest.(38,39)(6) Delay to diagnosis or treatment rate Two studies focused on disparities in time to a diagnostic procedure (CT scan for stroke)(36) and to de nitive treatment (time to permanent pacemaker implementation for emergency cases).(40  In-hospital mortality was used to re ect the quality of care during emergency care or surgery as reported in three articles identi ed in our review.(39,42,43) One distinguishes in-hospital mortality from failure to rescue, which occurs when a patient dies as a result of a major adverse event and seems, therefore, to be more sensitive to assess differences in quality of emergency care or surgery.(42 The different emergency care equity indicators are summarized in Table 1.

Socio-Economic Determinants of Health (SEDH)
The articles included in this review analysed health care equity based on seven SEDH: Insurance status, social deprivation, income, education level, social class, health literacy and nancial and non-nancial barriers.(Additional le 4) They covered the ve abilities considered by Levesque et al. (Figure 1), as mentioned in brackets and italics at the end of each paragraph.
Overall, the three main SEDH used to analyse health care equity across the 29 included studies were health insurance status, indices of social deprivation and income, and eight studies (28%) used more than one SEDH in their health care equity-focused analysis.

A. Insurance status
Insurance coverage as a relevant SEDH was approached in diverse ways amongst the 16 articles that used it including comparing outcomes between uninsured and insured individuals, (24,30) between publicly and privately insured individuals, (33,(38)(39)(40)46,49) or between uninsured, publicly and privately insured individuals.(23,25,35,(41)(42)(43)47,48) Present in more than half (55%) of the studies analysed, it is the most widely used SEDH in analyses of health care equity identi ed in this review.(It re ects the ability to pay in Levesque's framework).

B. Social deprivation (indices of area deprivation)
This SEDH represents the diverse social and economic conditions in which people live.This group was composed of different socio-economic deprivation indices including the "Index of Multiple Deprivation" [1], (10,44,45) "Carstairs Index" [2], (31,36) "Index of Marginalization area" [3], (27) "INSPQ deprivation Index" [4], (28,34) "area-based socioeconomic status quintile index" [5],(48) and "CT/10"[6] (26) These various tools take into account information about income, education, access to services, community safety, and physical environment.These indices are not assessed at the individual-level, but are instead area-based indices at the level of neighbourhoods, communities or health care regions.(Additional le 4 for details) More than half of included studies (59%) analysed health care equity through this SEDH.(It re ects abilities to reach and to pay).

C. Income
To measure income differences, four studies that used this SEDH used median income household (divided into quartiles or thirds) (41,43,46,47) and one used presence versus absence of a reportable income.(50)(It re ects the ability to reach and to pay).

D. Education level
Depending on the studies, the education level was divided into three or four categories ranging from never attended school to graduate degree.(37,49) (Additional le 4 for details) (It re ects the ability to perceive, to seek and to engage).

E. Social class
This SDEH is de ned hierarchically into six classes in descending order: professional, managerial, skilled non-manual, skilled manual, semi-skilled manual, non-skilled manual.This SEDH was used in one study to analyse health care equity.(31)(It re ects the ability to reach and pay).

F. Health literacy
In one study, health literacy was the SEDH used in the health equity-focused analysis, based on scores obtained through the Rapid Estimate of Adult Literacy in Medicine test, a reading recognition test comprised of 66 health-related words arranged in ascending order of di culty.(32)(It re ects the ability to perceive and engage).

G. Financial and non-nancial barriers
In one paper, these two types of barriers were used based on subjects' responses to 14 questions (7 questions each) relating to nancial concerns [7] and non-nancial barriers[8].(29)(It re ects the ability to reach and to pay).

Addressing health care equity through the association of emergency care indicators and SEDH
The bias assessment revealed two signi cant risks of bias across studies.First of all, there is a risk for confounding related to the use of retrospectively collected administrative data used across all included studies as you can only adjust for variables that were collected.If potential confounding variables were not collected, they cannot be accounted for.For example, the almost systematic absence of precise clinical diagnoses in administrative data undermines the ability to accurately estimate the health of selected populations and therefore does not allow for a correct adjustment between compared groups.
Secondly, comparisons between studies are biased by the fact that for the same variable, data are not collected in a standardised manner.This information bias concerns all SEDH variables, but is particularly relevant for the socio-economic level, which is often analysed using indices that include many variables that differ between studies.
Because of this signi cant heterogeneity associated with the large number of outcomes and exposures (our systematic review highlighted 14 different indicators and 7 SEDH), we decided not to carry out a meta-analysis.
However, the last two columns of Additional le 4 present the statistical data and associated conclusions of the 29 reviewed studies.It can thus be seen that across all studies, all identi ed SEDH were found to be associated with statistically signi cant differences in emergency care indicators.Descriptive examples of associations between equity indicators and some of the main SEDH identi ed in this review are described below.The group of each indicator is indicated in bold and in brackets.

A. Health insurance
In a large retrospective study including over 2.2 million patients, Lines et al. demonstrated that patients with public insurance are 2.5 times more likely to have preventable ED visits (Group 1) than private patients (Rate ratio 2.53, 95%CI 2.49-2.56).(33) Similarly, in another large retrospective cohort of 1.3 millions patients, Metcalfe et al. highlighted a statistically signi cant association between in-hospital mortality (Group 3) and insurance status amongst patients presenting to hospital with acute surgical conditions requiring emergency surgery whereby uninsured patients were at signi cantly higher risk of death than privately insured patients (Odds Ratio 1.28, 95%CI 1.16-1.41).(42) However, some studies do not show signi cant differences in access or quality of care based on insurance coverage.(38,41)Further, among the studies comparing patients with and without insurance coverage, two have shown an increase in the use of ED (Group 1) after the introduction of public insurance coverage for previously uninsured patients.For example, DeLeire et al. found an increase in total ED visits (Group 1) of 46% (p-value, p<0.01) and ACSCs ED visits (Group 1) of 38.7% (p-value, p<0.01) after the introduction of a public insurance (Medicaid) among low-income childless adults.(24) Authors postulate that this may be due to insurance coverage increasing one's access to outpatient care, but also to ED-based care.Similarly, Kerr et al., who compared ED visits rate (Group 1) amongst a cohort of HIV-positive patients with varying health insurance coverage (n=4,947), showed that uninsured patients used the ED signi cantly less than privately insured patients (Incidence rate ratio (IRR) 0.65, 95%CI 0.61-0.70),but that patients with Medicaid (public insurance program in the US) used the ED more frequently (IRR 1.26, 95% CI 1.18-1.36).(25)

B. Social deprivation
Although social deprivation is measured by many different area-level indices among studies, it appears to be signi cantly associated with the three categories of indicators of emergency care identi ed in this review.For example, Vanasse et al. show a relative risk of ED visits (Group 1) of 3.82 among women with mood disorders in Québec of the most deprived quintile in comparison with women of the least deprived quintile (based on an index combining social and material deprivation).(28)Then Lazzarino et al., who used the Carstairs Index, highlighted a signi cant difference in the likelihood of having a brain scan on the day of admission (Group 2) for patients presenting to the ED with an acute stroke between the least and the most deprived quartiles (Odds ratio 0.94, 95%CI 0.89-0.99).(36)Similarly, Thorne et al. demonstrate a signi cant association between 30-day mortality (Group 4) after ED admissions for hip fracture and social deprivation quintile with patients in the most deprived quintile at higher risk than those in the least deprived quintile, based on the Index of Multiple Deprivation (Odds ratio 1.19, 95%CI 1.15-1.23).(45)

C. Income
Findings regarding median household income were mixed across studies.Among the four studies using this SEDH, two demonstrated signi cant associations between median household income and emergency care indicators (43,47) and the other two did not.(41,46)(See Additional le 4)

D. Education level and Health Literacy
Contrary to expectations, only two studies assess this SEDH, including one with a small sample of patients (n=647), which found that lower education level was potentially associated with an increased risk of being an "emergency presenters" (de ned as presenting to ED around the time of a new cancer diagnosis) (group 1).( 49) The other study, by Stecksen et al. highlighted that access to reperfusion therapy (group 2) for stroke is associated with higher patient education level (Odds ratio 1.14, 95%CI 1.03-1.26).(37) Only one study analysed the impact of health literacy on potentially preventable ED visits and found that patients with poor health literacy are approximately twice as likely to have preventable ED visits (group 1) than patients with adequate health literacy, even after adjustment for relevant confounding factors (Rate Ratio 1.93, 95%CI 1.55-2.40).(32) [1] A composite score originates from the following domain indices: income, employment, health, education, access to services, community safety and physical environment.
[2] An index of deprivation used in spatial epidemiology, based on four variables (Male unemployment, Lack of car ownership, Overcrowding and Low social class).
[3] A validated census-and geography-based index that measures marginalization at the level of the census dissemination area, including economic, ethno-racial, age-based and social marginalization [4] Institut national de la santé publique du Québec (INSPQ) deprivation index: an index based on six socioeconomic indicators calculated at the dissemination area (DA) level.This index has two components, material and social.The material component is based on the proportion of people without a high school diploma, the employment-to-population ratio and the average income.The social component is based on the proportion of people living alone, the proportion of separated, divorced or widowed people and the proportion of lone-parent families [5] Area-based SES quintile : an index of seven components based on American Community Survey (Education index, percent persons above 200% poverty line, percent persons with a blue collar job, percent persons employed, median rental, median value of owner-occupied housing unit and median household income) [6] CT/10: a coe cient that refers to the effect of a 10% increase in the percentage of the population in the Census tract (CT) who have household incomes below 200% of the federal poverty threshold.(The poverty coe cient indicates the effect of a 10% increase in the fraction of the population living in poverty) [7] A set of seven self-reported nancial concerns items: "insurance won't cover care", "the respondent will have to pay more than expected", "he/she will have to pay more than he/she can afford", "medications will cost too much", "not being sure about being dropped from the public healthcare program", "not knowing what the health plan covers and not knowing where to go with questions about coverage".
[8] Seven self-reported non-nancial barriers including: transportation di culties, problems making appointments, not knowing where go for care, work/family responsibilities, o ce/clinics not being open at suitable times, obtaining childcare and not being able to utilize one's preferred provider.[9] For the purpose of this paper, the term "emergency admissions" is referring to a hospital admission following ED-based care or to a hospital admission for an emergency condition [10] ACSCs are conditions for which it is believed that timely and appropriate outpatient care could prevent disease complications, or worsening of disease conditions thereby preventing ED visits and hospital admissions

Iv. Discussion
Findings of this systematic review, which identi ed 14 health equity indicators and 7 SEDH, suggest that administrative data allows for a broad analysis of health care equity in emergency care settings.Using these health equity indicators, each of which measure different aspects of the patient pathway through emergency care, in combination with various SEDH described, presents a promising way forward in conducting health equity analyses of health care systems.Based on these ndings, we have created a conceptual framework for assessing health care equity, combining SEDH through different categories of emergency care indicators, depicted in Figure 3.

Emergency care Equity
The most frequently used indicator is ED visits/Emergency admissions but due to its lack of speci city, it must be interpreted with caution as there are notably many factors that could explain differences in ED visits or emergency admissions beyond health care equity, particularly differences in general health status and prevalence of diseases.(51)ACSC ED visits/ACSC emergency admissions is arguably more speci c as it focuses on ED visits/admissions that are potentially preventable with good access to primary care.(15,52) The indicators comprising Group 2 (indicators of quality of emergency care) directly analyse emergency care and are therefore more speci c in their measurement of health care equity in emergency care settings compared to indicators in Group 1.We found that they are used considerably less.This may re ect di culty in obtaining relevant data to measure these indicators through administrative datasets.
However, they might be useful indicators to use in future studies analysing health care equity.
Among outcome indicators (Group 3), in-hospital mortality seems to be the most reproducible and available administrative data-derived indicator.
Finally, 30/90/326-day mortality and ED readmission, which are more global equity indicators (Group 4) assess the lack of access to outpatient care following an ED visit, but also potential issues during the emergency care that lead to inequities in health outcome.
Due to the inherent di culties of measuring a complex concept like health care equity and the large number of potential confounding factors, using a combination of indicators instead of one sole indicator to measure health care equity in any given health care context is more likely to result in a well-rounded assessment.As such, we suggest combining indicators across the different groups when assessing health care equity.The choice of speci c indicators will depend on the context of the study, the study objectives and availability of administrative data (and relevant variables) in the health care setting of interest.

Socio-Economic Determinants of Health
Although median household income and education level appear to be common and reproducible measurements, many studies chose to use speci c area-level indices that account for multiple domains of deprivation experienced by the target population.These indices combine different parameters to assess deprivation, such as income, employment status, living environment deprivation, and education.These indices are less reproducible than median household income since they require many more variables for their calculation (which may not be available in all health care administrative datasets), but they are arguably better at measuring inequities due to the broad domains of deprivation they assess.
To assess the accessibility of health care services, one particular SEDH emerged: insurance status.Most of the studies analysing this SEDH were published in the US.We assume that this is due to the speci cities of the US health care system and the different health insurance reforms (most notably the Affordable Care Act), (53) which make this a very relevant SEDH in the US context.Despite most of the studies being US-based, this SEDH seems relevant to most health care systems in high-income countries, even those with universal health care coverage, where some individuals are able to access private insurance that covers additional bene ts, therefore creating potential inequities.(54) As such, this SEDH could be used more widely than currently represented in the literature.

Perspectives and implications
An important implication of our research is the identi cation of four groups of indicators that can be used to analyse health care equity in emergency care of high-income countries.As most of the indicators identi ed in this review are not speci c to emergency care settings, it seems possible to study health care equity in other areas of the health care system of high-income countries with similar administrative dataderived indicators, as for example hospitalization,(55,56) ACSCs during the total hospital admission, (57) and wait times.(52)Such information could be useful for policy makers or health equity researchers to ll the gap in data about health care equity within different health care settings, particularly in high-income countries, using available administrative data.
Our ndings suggest that SEDH have a considerable impact on health care equity.The next step would also be to better characterize root causes for differences in emergency care utilization that lie outside the health care system.For example, in a recent study, McCormick et al. demonstrate that emergency admissions are primarily due to a higher prevalence of illness in disadvantaged areas,(51) while Pollack et al. who analysed the relationship between neighbourhood poverty and ED use in a 21-year randomized social experiment did not nd a consistently signi cant connection between neighbourhood poverty and ED use.(58)More studies like these are needed to improve our understanding of the complex interconnectedness between SEDH, health care use and health care equity.

Limitations
Our review has some limitations that require consideration.First, the content and quality of administrative datasets are highly variable within countries (sometimes even within regions) and between countries.As such, many of the indicators identi ed in our review might not be available in many health care settings, reducing their generalizability and widespread applicability.However, important equity indicators such as preventable ED visits are frequently used and easily replicable between countries.Secondly, administrative data are not designed for the purpose of equity monitoring, which implies a lack of robust quality control of the collected data, a time lag in data availability, differences in concepts and de nitions used between datasets limiting comparability, and the possibility of missing records.To address this, further studies of health equity indicators and SEDH using different types of datasets would be helpful for the researchers.Third, in order to de ne the criteria relevant to this review, it was necessary to make many normative choices before data analysis.Our focus has been indeed solely on SEDH and their associated inequities.It would also be important to analyse equity, in complementary studies, through determinants of health such as race/ethnicity, gender, or place of residence, in order to have a comprehensive picture of health care equity.As such, these results must be interpreted in the context of the concept of health care equity and the de nitions we used.
Lastly, as more than the half of the studies was conducted in the US, the extrapolation of the results should be carefully interpreted.

V. Conclusion
Measuring health care equity should be an integral component of all comprehensive assessments of a health care system's performance.However, in order to measure health care equity, indicators for making such measurements need to be identi ed, as was the goal of this review.Such indicators can be used by researchers and policy makers interested in measuring health care equity through thoughtful selection of the most relevant indicators de ned by the local context and stated objectives.Using a combination of indicators is likely to lead to a more comprehensive, well-rounded analysis of health care equity than using any one indicator in isolation.Though studies analysed focused on emergency care settings, it seems possible to extrapolate these indicators to measure equity in other areas of the health care system.Meta-analyses focusing on speci c socio-economic determinants of health such as health insurance coverage, income or indices of social deprivation in combination with studies analysing factors that could in uence the use of emergency care related to social inequalities would help to further characterize root causes of ongoing health care inequity in health care systems.
al. (22): A. Equity indicators of poor access to outpatient care (indicators "prior to emergency care") (Group 1) B. Equity indicators of quality of emergency care (indicators "during emergency care") (Group 2) C. Equity indicators of clinical outcomes (indicators "following emergency care") (Group 3) D. Global Equity indicators (Group 4) A. Equity indicators of poor access to outpatient care (Group 1)

( 3 )
Frequent ED visits One study used this indicator considering frequent ED visits when 4 or more ED visits occurred by an individual per year.(34)(4) ED-associated initial diagnosis rate This indicator compared the rate of initial diagnosis of cancer in the ED between different SEDH.(35)B. Equity indicators of quality of emergency care (Group 2)

) ( 7 )
Missed diagnoses in ED rateThis indicator, used in one study, highlighted disparities of missed diagnoses of acute myocardial infarction according to insurance status or median household income.(41)C. Equity indicators of outcome after emergency care (Group 3) This third group of indicators includes indicators of outcome disparities.We identi ed six outcome indicators.(8) Major adverse event rateThis indicator was used in 2 studies that analysed emergency general surgery.(42,43)It represented the rate of speci c complications following an emergency general surgery including cerebrovascular accident, pneumonia, pulmonary embolus, acute respiratory distress syndrome, renal failure, urinary tract infection, myocardial infarction, sepsis, septic shock and cardiac arrest.

( 9 )
In-hospital mortality and (10) failure to rescue rate

) ( 11 )
Neurological recovery rate This speci c indicator was used in one study analysing the neurological recovery over time of patients who presented to the ED with a cardiac arrest.(39)(12) Length of stay/Bed days (after emergency admission) Although these are traditional indicators of hospital care quality, they are used in one study that analysed inequities following emergency admission according to social deprivation.(44)D. Global Equity indicators As they could re ect a lack of outpatient care following a discharge post-admission and/or poor quality of care during an emergency admission, these following indicators could apply to the three different groups of indicators.(13) 30/90/365-day mortality rate One study analysed 30-/90-/365-day mortality following emergency admission for hip fracture, re ecting quality of ED-and hospital-based care, as well as access to and quality of ambulatory follow-up care post-discharge.(45)(14) ED readmissions rate/Emergency reshopitalisation rate This indicator was used in three articles.Two of them analysed ED readmissions within 30 days postdischarge.(46,47)One used this indicator to analyse the rate of hospital admissions through the ED in the year following a diagnosis of breast, colorectal, non-small cell lung or pancreatic cancer.(48)Overall, indicators of access to outpatient care and particularly ED visits and emergency admission and ACSCs ED visits/ACSCs emergency admissions were the most frequent indicators used across studies.

Figure 1 Framework
Figure 1

Figure 2 Flow
Figure 2

Table 1 .
Emergency Care Equity indicators List of the different equity indicators divided in three categories.The first category represent indicators of access to high quality outpatient care.The second category represents the indicators of quality of emergency care.The last category represent the outcome indicators following emergency care.The two last indicators, because of their broadness are included in the 3 groups