Reporting of equity in observational epidemiology: A methodological review

Background Observational studies can inform how we understand and address persisting health inequities through the collection, reporting and analysis of health equity factors. However, the extent to which the analysis and reporting of equity-relevant aspects in observational research are generally unknown. Thus, we aimed to systematically evaluate how equity-relevant observational studies reported equity considerations in the study design and analyses. Methods We searched MEDLINE for health equity-relevant observational studies from January 2020 to March 2022, resulting in 16 828 articles. We randomly selected 320 studies, ensuring a balance in focus on populations experiencing inequities, country income settings, and coronavirus disease 2019 (COVID-19) topic. We extracted information on study design and analysis methods. Results The bulk of the studies were conducted in North America (n = 95, 30%), followed by Europe and Central Asia (n = 55, 17%). Half of the studies (n = 171, 53%) addressed general health and well-being, while 49 (15%) focused on mental health conditions. Two-thirds of the studies (n = 220, 69%) were cross-sectional. Eight (3%) engaged with populations experiencing inequities, while 22 (29%) adapted recruitment methods to reach these populations. Further, 67 studies (21%) examined interaction effects primarily related to race or ethnicity (48%). Two-thirds of the studies (72%) adjusted for characteristics associated with inequities, and 18 studies (6%) used flow diagrams to depict how populations experiencing inequities progressed throughout the studies. Conclusions Despite over 80% of the equity-focused observational studies providing a rationale for a focus on health equity, reporting of study design features relevant to health equity ranged from 0–95%, with over half of the items reported by less than one-quarter of studies. This methodological study is a baseline assessment to inform the development of an equity-focussed reporting guideline for observational studies as an extension of the well-known Strengthening Reporting of Observational Studies in Epidemiology (STROBE) guideline.


Rationale
3 Describe the rationale for the review in the context of what is already known.
Describe assumptions about mechanism(s) by which the intervention is assumed to have an impact on health equity.

3A
Provide the logic model/analytical framework, if done, to show the pathways through which the intervention is assumed to affect health equity and how it was developed.
NA Objectives 4 Provide an explicit statement of questions being addressed with reference to participants, interventions, comparisons, outcomes, and study design (PICOS).
Describe how disadvantage was defined if used as criterion in the review (e.g. for selecting studies, conducting analyses or judging applicability).

9, appendix III 4A
State the research questions being addressed with reference to health equity 9

Protocol and registration
5 Indicate if a review protocol exists, if and where it can be accessed (e.g., Web address), and, if available, provide registration information including registration number.Eligibility criteria 6 6.Specify study characteristics (e.g., PICOS, length of follow-up) and report characteristics (e.g., years considered, language, publication status) used as criteria for eligibility, giving rationale.
Describe the rationale for including particular study designs related to equity research questions.

6A
Describe the rationale for including the outcomes -e.g.how these are relevant to reducing inequity.

Information sources
Describe all information sources (e.g., databases with dates of coverage, contact with study authors to identify additional studies) in the search and date last searched.
Describe information sources (e.g.health, non-health, and grey literature sources) that were searched that are of specific relevance to address the equity questions of the review.

Search
Present full electronic search strategy for at least one database, including any limits used, such that it could be repeated.
Describe the broad search strategy and terms used to address equity questions of the review.

Study selection
State the process for selecting studies (i.e., screening, eligibility, included in systematic review, and, if applicable, included in the meta-analysis).

Data collection process
Describe method of data extraction from reports (e.g., piloted forms, independently, in duplicate) and any processes for obtaining and confirming data from investigators.

Data items
List and define all variables for which data were sought (e.g., PICOS, funding sources) and any assumptions and simplifications made.
List and define data items related to equity, where such data were sought (e.g. using PROGRESS-Plus or other criteria, context).

Risk of bias in individual studies
Describe methods used for assessing risk of bias of individual studies (including specification of whether this was done at the study or outcome level), and how this information is to be used in any data synthesis.

Summary measures
State the principal summary measures (e.g., risk ratio, difference in means).

Synthesis of results
Describe the methods of handling data and combining results of studies, if done, including measures of consistency (e.g., I 2 ) for each meta-analysis.
Describe methods of synthesizing findings on health inequities (e.g.presenting both relative and absolute differences between groups).
12 Risk of bias 15.Specify any assessment of risk of bias that may affect the cumulative evidence across studies (e.g., publication bias, selective reporting within studies).

Additional analyses
Describe methods of additional analyses (e.g., sensitivity or subgroup analyses, meta-regression), if done, indicating which were pre-specified.
Describe methods of additional synthesis approaches related to equity questions, if done, indicating which were pre-specified

Study selection
Give numbers of studies screened, assessed for eligibility, and included in the review, with reasons for exclusions at each stage, ideally with a flow diagram.

Study characteristics
For each study, present characteristics for which data were extracted (e.g., study size, PICOS, follow-up period) and provide the citations.
Present the population characteristics that relate to the equity questions across the relevant PROGRESS-Plus or other factors of interest.

Risk of bias within studies
Present data on risk of bias of each study and, if available, any outcome level assessment (see item 12).

Results of individual studies
For all outcomes considered (benefits or harms), present, for each study: (a) simple summary data for each intervention group (b) effect estimates and confidence intervals, ideally with a forest plot.

Synthesis of results
Present results of each meta-analysis done, including confidence intervals and measures of consistency.
Present the results of synthesizing findings on inequities (see 14).

Risk of bias across studies
Present results of any assessment of risk of bias across studies (see Item 15).

Additional analysis
Give results of additional analyses, if done (e.g., sensitivity or subgroup analyses, meta-regression [see Item 16]).
Give the results of additional synthesis approaches related to equity objectives, if done, (see 16).

Summary of evidence
Summarize the main findings including the strength of evidence for each main outcome; consider their relevance to key groups (e.g., healthcare providers, users, and policy makers).

Limitations
Discuss limitations at study and outcome level (e.g., risk of bias), and at review-level (e.g., incomplete retrieval of identified research, reporting bias).

Conclusions
Provide a general interpretation of the results in the context of other evidence, and implications for future research.
Present extent and limits of applicability to disadvantaged populations of interest and describe the evidence and logic underlying those judgments.

26A
Provide implications for research, practice or policy related to equity where relevant (e.g.types of research needed to address unanswered questions).INTRODUCTION Rationale 3 Describe the rationale for the review in the context of existing knowledge.7 Objectives 4 Provide an explicit statement of the objective(s) or question(s) the review addresses.

Eligibility criteria
5 Specify the inclusion and exclusion criteria for the review and how studies were grouped for the syntheses.

10
Information sources 6 Specify all databases, registers, websites, organisations, reference lists and other sources searched or consulted to identify studies.Specify the date when each source was last searched or consulted.

10-11
Search strategy 7 Present the full search strategies for all databases, registers and websites, including any filters and limits used.

Appendix I
Selection process 8 Specify the methods used to decide whether a study met the inclusion criteria of the review, including how many reviewers screened each record and each report retrieved, whether they worked independently, and if applicable, details of automation tools used in the process.

11
Data collection process 9 Specify the methods used to collect data from reports, including how many reviewers collected data from each report, whether they worked independently, any processes for obtaining or confirming data from study investigators, and if applicable, details of automation tools used in the process.

11
Data items 10a List and define all outcomes for which data were sought.Specify whether all results that were compatible with each outcome domain in each study were sought (e.g. for all measures, time points, analyses), and if not, the methods used to decide which results to collect.

11-12
10b List and define all other variables for which data were sought (e.g.participant and intervention characteristics, funding sources).Describe any assumptions made about any missing or unclear information.

11-12
Study risk of bias assessment 11 Specify the methods used to assess risk of bias in the included studies, including details of the tool(s) used, how many reviewers assessed each study and whether they worked independently, and if applicable, details of automation tools used in the process.

NA Effect measures
Synthesis methods 13a Describe the processes used to decide which studies were eligible for each synthesis (e.g.tabulating the study intervention characteristics and comparing against the planned groups for each synthesis (item #5)).

NA
13b Describe any methods required to prepare the data for presentation or synthesis, such as handling of missing summary statistics, or data conversions.

NA
13c Describe any methods used to tabulate or visually display results of individual studies and syntheses.12 13d Describe any methods used to synthesize results and provide a rationale for the choice(s).If metaanalysis was performed, describe the model(s), method(s) to identify the presence and extent of statistical heterogeneity, and software package(s) used.

NA
13e Describe any methods used to explore possible causes of heterogeneity among study results (e.g.subgroup analysis, meta-regression).

NA
13f Describe any sensitivity analyses conducted to assess robustness of the synthesized results.NA Reporting bias assessment 14 Describe any methods used to assess risk of bias due to missing results in a synthesis (arising from reporting biases).

NA
Certainty assessment 15 Describe any methods used to assess certainty (or confidence) in the body of evidence for an outcome.NA

Study selection 16a
Describe the results of the search and selection process, from the number of records identified in the search to the number of studies included in the review, ideally using a flow diagram.
12 16b Cite studies that might appear to meet the inclusion criteria, but which were excluded, and explain why they were excluded.

Study characteristics 17
Cite each included study and present its characteristics.NA Risk of bias in studies 18 Present assessments of risk of bias for each included study.NA

Results of individual studies
19 For all outcomes, present, for each study: (a) summary statistics for each group (where appropriate) and (b) an effect estimate and its precision (e.g.confidence/credible interval), ideally using structured tables or plots.

12-16
Results of syntheses 20a For each synthesis, briefly summarise the characteristics and risk of bias among contributing studies.NA 20b Present results of all statistical syntheses conducted.If meta-analysis was done, present for each the summary estimate and its precision (e.g.confidence/credible interval) and measures of statistical heterogeneity.If comparing groups, describe the direction of the effect.

Registration and protocol
24a Provide registration information for the review, including register name and registration number, or state that the review was not registered.

9
24b Indicate where the review protocol can be accessed, or state that a protocol was not prepared.9 24c Describe and explain any amendments to information provided at registration or in the protocol.9 Support 25 Describe sources of financial or non-financial support for the review, and the role of the funders or sponsors in the review.

Supplementary appendix V. Supplementary methods Definitions
Health inequity: Health inequity is defined as avoidable and unfair differences in health.

Context:
We defined context as a set of external characteristics that surround an implementation effort (not a part of it) and could impact the effects of the intervention.This would include healthcare system characteristics, institutional setting; and the wider sociopolitical, economic, and cultural infrastructure.
Health equity relevant studies: We define health equity relevant as studies that focus on individuals or populations experiencing inequities or studies of mixed populations that analyzed at least one health outcome across one or more PROGRESS factor.We define health outcomes according to the WHO definition, as "changes as in health status that result from the provision of health services".This includes studies focused on populations experiencing inequities such as people who experience homelessness and asylum seekers, as well as studies which present disaggregated results or evaluate outcomes across one or more PROGRESS factors.However, studies which control for PROGRESS in analyses without analyzing differences across the factors are not considered equity relevant.For example, studies of breast cancer in women would not be considered health equity-relevant since women are not disadvantaged in opportunities for health as it relates to breast cancer care.However, if stratified analysis was done to compare mortality of women living in rural vs urban area (or other PROGRESS factors), the study would be considered equity relevant.Similarly, a study of low-income or racialized women accessing breast cancer care would be considered health equity-relevant because they experience different opportunities in obtaining care.
Observational studies: We define observational studies as analytical or descriptive studies evaluating a research question without changing exposure to an intervention.Observational studies are classified in the STROBE reporting guideline into three types: 1) cohort: following an exposed population over time; 2) case-control: comparing exposures between people with a particular disease outcome (cases) and people without that outcome (controls); and 3) cross sectional: assessing all individuals in a sample at the same point in time.Studies conducted using routinely collected data stored in administrative datasets can be classified into these three types of studies.

Sampling strategy
Following consultations with our interdisciplinary team, including researchers, decision-makers, and representatives from the patient and public community, we devised a three-factor randomized sampling approach to ensure balance in our study selection across key phenomena that were agreed upon to influence the reporting of health equity considerations in the studies.This we wanted to ensure their equal representation in our study sample.
We balanced across the following factors: 1. Studies conducted in high-income countries (HIC) and low-and middle-income countries (LMIC) based on the World Bank classification.2. Studies focused on COVID-19 and those that are not.3. Studies focused on populations experiencing inequities and those that stratify their analyses.
The decision to balance by country was grounded in the recognition of the pivotal role that context and resources play in LMIC settings, influencing health inequities within LMIC in comparison to HIC.As for choosingCOVID-19 studies as a factor, we effort to balance studies related to COVID-19 or unrelated to it our strategy includes a deliberate given the documented exacerbation of inequities during the COVID-19 pandemic.
Although our sampling strategy is based on three factors, our comprehensive assessment will encompass all aspects of PROGRESS-Plus in the included studies.Consequently, populations experiencing various forms of inequities, such as those with low income, homelessness, migrants, asylum-seekers, and racialized individuals, will be included.

Sample size
To ensure a representative sample for comparable results, we employed a random selection process supported by a sample size calculation for binary outcomes (pertaining to categorical considerations of equity in the studies).We based our calculation on 95% confidence intervals with a margin of ± 6% for observed proportions of 50%, assuming that half of the studies would report at least one PROGRESS characteristic.According to our calculations, a sample of 320 studies would be sufficient for our study and that sample size aligns with similar studies in the literature.We are aware that our study lacks sufficient power for making comparisons across the three prioritized groups; therefore, we analyzed the data combined.Are the limits or extent of applicability of the findings described across one or more PROGRESS-Plus characteristics?

LMIC
"Reducing any of the five MetS [Metabolic Syndrome] components, while taking into account the differences found by socio-economic and workplace characteristics, should be one priority for reducing MetS prevalence." Study Title: Prevalence and determinants of metabolic syndrome in Spanish salaried workers: evidence from 15 614 men and women Was health equity considered in framing the reason for the study?(i.e.across at least one PROGRESS-Plus characteristic)?Difference in disease burden (includes incidence, prevalence, progression, mortality, etc…) "However, when trends for White women are compared with trends for women of other races and Hispanic ethnicity, long-standing racial disparities in breast cancer mortality are evident through descriptive analyses of surveillance data with greater mortality declines observed for White women."

Study title: Recent Changes in the Patterns of Breast Cancer as a Proportion of All Deaths According to Race and Ethnicity
Difference in access (coverage, services, timeliness, and workforce) "Variations in access to breast cancer care by race and ethnicity have been documented in numerous studies farther along the cancer care continuum including follow-up after an abnormal exam, 9- 11 timeliness of initiation of treatment, 12,13 and concordance of therapy with recommended guidelines. 14"

Difference in effects
"Our previous analyses comparing cardiovascular, cerebrovascular, microvascular, and all-cause mortality outcomes by medication adherence status among veterans with diabetes revealed that while many outcomes were improved by higher rates of medication use, adherence did not prevent all targeted outcomes. 12Moreover, when adjusting for patient characteristics and first-year medication adherence, differences in outcomes were observed in subgroups of this population, including minorities and those residing in different geographical regions." Study Title: Racial and Regional Disparities in Outcomes Among Veterans Initially Adherent to Oral Antidiabetic Therapies: an Observational Cohort Study Is equity described in the theory of how the intervention/exposure is expected to work? (e.g. in the clinical pathway or logic model) "Studies have repeatedly demonstrated that Black patients are diagnosed with higher T and N category disease than non-Black patients, and this likely contributes to inferior outcomes. 4,7,8lthough factors such as genetic predisposition and an increased prevalence of risk factors (tobacco and alcohol) may contribute to racial disparities, 7,9,10   WilsonGenderson & Pruchno, 2013), Neighborhood fear is based on respondents' answers to statements about the safety of their respective neighborhood community, such that a higher averaged score indicates less safety and greater fear.Social cohesion refers to the degree of relational trust with neighbors and the level of intimacy with them (Ahern & Galea, 2011; Elliott et  al., 2014)" Study title: Exploring the contingent associations between functional limitations and depressive symptoms across residential context: a multilevel panel data analysis For matched cohort studies, did the authors use any PROGRESS-Plus characteristics for matching?How were they determined and what was the rationale?
Males and females were matched for age, race and key comorbidities in order to account for differences in baseline characteristics between the 2 groups.

Study title: Sex Differences in Case Fatality Rate of COVID-19: Insights From a Multinational Registry
Did the authors report that outcomes were identified as relevant and important to populations experiencing inequities?"The primary outcome was defined to be the location of death: (1) home, (2) acute care, or (3) PCU or residential hospice.""This is especially important given that some studies suggest that quality of death at home is higher than that in institutional settings."Participants self-reported their gender (woman or man) and all analyses were carried out following the international recommendations on gender in public-health research [27-30]."

Study title: Gender Differences in the Association between Physical Inactivity and Mental-Health Conditions in People with Vision or Hearing Impairment
Did the authors report efforts to reduce selection bias across PROGRESS-Plus? "Obesity was defined as BMI ≥28 kg/m2 .Central obesity was defined as a waist circumference ≥90 cm in males and ≥80 cm in females, respectively, according to WHO recommendations for Asian adults." of all investigations of possible causes of heterogeneity among study results.NA 20d Present results of all sensitivity analyses conducted to assess the robustness of the synthesized results.NA Reporting biases 21 Present assessments of risk of bias due to missing results (arising from reporting biases) for each synthesis assessed.NA Certainty of evidence 22 Present assessments of certainty (or confidence) in the body of evidence for each outcome assessed.NA DISCUSSION Discussion 23a Provide a general interpretation of the results in the context of other evidence.16-18 23b Discuss any limitations of the evidence included in the review.16-18 23c Discuss any limitations of the review processes used.16-18 23d Discuss implications of the results for practice, policy, and future research.16-18 OTHER INFORMATION sample described across one or more PROGRESS-Plus characteristics?"The sample comprised 418 non-Hispanic white and 154 Hispanic women."

"
Students were invited to participate via personal invitation to their parents and/or guardians."Study title: Gender differences in blood pressure and body composition in schoolchildren ascendants from Amerindian and European Did the authors describe inclusion/exclusion criteria across PROGRESS-Plus characteristics?"We excluded type 2 diabetes related to pregnancy and participants aged < 18 years (n = 16 133) and cases with missing georeferencing information (n = 13776), leaving a total of 137 820 adults in the study."Study title: Regional variation in type 2 diabetes: evidence from 137 820 adults on the role of neighbourhood body mass index Did the authors describe the context of the study in relation to health equity?"In addition to the individual-level predictors, four neighborhood-environmental variables are included to capture contextual effects: Neighborhood fear, Social cohesion, Residential stability, and Structural disadvantage.Consistent with the extant literature (Jones et al., 2014; 10 " Study title: The Impact of Socioeconomic Status on Place of Death Among Patients Receiving Home Palliative Care in Toronto, Canada: A Retrospective Cohort Study Did the authors report how population characteristics were obtained?(e.g.age) Did the authors report the use of any PROGRESSplus characteristics in the determination of the study sample size?"AfricanAmerican and Hispanic households were oversampled at about twice the rate of Whites to account for unequal probability sampling during HRS study recruitment(Fisher & Ryan, 2018;  Ofstedal & Weir, 2011)"Study title: Association of Parenthood With Incident Heart Disease in United States' Older Men and Women: A Longitudinal Analysis of Health and Retirement Study DataDid the authors plan any analyses to explore differences or similarities in effects across PROGRESS-Plus characteristics?"The prevalence with confidence intervals of CHD and its risk factors is presented by area (urban/rural), gender and survey period."Studytitle: Change in prevalence of CoronaryHeart Disease and its risk between 1991-94 to 2010-12 among rural and urban population of National Capital Region, Delhi Did the authors describe the use of context for analysis?"Weconducted 2 sets of multivariable models, the first minimally adjusted for age, parity, neighborhood income quintile, and rurality,…"Study title: Association of Preexisting Disability With Severe Maternal Morbidity or Mortality in Ontario, CanadaIn statistical models, did the authors use any PROGRESS-Plus characteristics for covariate adjustment?"Candidate sociodemographic and pregnancyrelated predictor variables were selected a priori based on our conceptual model of predictors and consequences of preterm birth and SMM (FigureA1) and administratively available variables.Maternal sociodemographic factors from birth certificates included: age at delivery, race/ethnicity, educational attainment, delivery payer, and urban or rural residence based on Federal Information Processing Standard (FIPS) county codes."Study title: A population-based study to identify the prevalence and correlates of the dual burden of severe maternal morbidity and preterm birth in California Did the authors report missing data related to individuals or contextual factors associated with health inequities?"The amount of missing data for our measures is small.Age and sex have no missing values.Education is missing for 322 observations (0.2%).The 225 cases missing race information are coded as "other" and 57 missing wealth observations are coded as the mean for the respective wave."Study title: Persistent, Consistent, and Extensive: The Trend of Increasing Pain Prevalence in Older Americans Did the authors describe losses or exclusions of participants across PROGRESS-Plus characteristics?"Attrition analyses reveal that age and baseline anxiety increase the likelihood of nonresponse in subsequent waves, whereas home ownership decreases it."Study title: Mental health of older widows and widowers: Which coping strategies are most protective?"We excluded…those who identified as Alaskan Native or American Indian or 'Other' Race (n=6,673) due to small numbers"Study title: Racial and Ethnic Disparities in Health of Adults in the United States: A 20-Year National Health Interview Survey Analysis, 1999-2018 Did the authors present the flow of participants across PROGRESS-Plus characteristics?"A total 604 students within the age range were included in the enrollment stage.Sixty-four students were excluded according to the exclusion criteria, N = 33 Mapuches and N = 31 from the European group.The remaining students were separated by gender as follow; Mapuches (N = 119, boys, N = 55; girls, N = 64), and European group (N = 421, boys, N = 199; girls, N = 222

Study title: Association of Race and Health Care System With Disease Stage and Survival in Veterans With Larynx Cancer
we postulate that differences in access to health care play a major role in racial disparities in cancer outcomes."

The Impact of Socioeconomic Status on Place of Death Among Patients Receiving Home Palliative Care in Toronto, Canada: A Retrospective Cohort
)."