How Site Location Influences Diversity in Clinical Trial Enrollment

Introduction: The Link Between Geography and Inclusion

Diversity in clinical trial enrollment is now a regulatory priority, a scientific necessity, and an ethical obligation. Yet, one of the most overlooked factors influencing diversity is site location. Where a trial is conducted has a direct impact on who has access to participate. Sponsors that select sites in non-diverse or high-barrier regions often fail to recruit a representative population, leading to biased outcomes and delayed regulatory approval.

This article explores the critical role of site geography in fostering or hindering diverse patient enrollment and outlines actionable strategies to align location planning with diversity, equity, and inclusion (DEI) goals.

1. Understanding Diversity Metrics in Clinical Trials

Diversity in clinical research encompasses several dimensions:

• Race and Ethnicity (e.g., African American, Asian, Hispanic/Latino)
• Age (e.g., inclusion of elderly and pediatric populations)
• Sex and Gender
• Socioeconomic Status (access to care, insurance, housing)
• Geography (urban vs rural, regionally underserved populations)

Site location influences nearly all of these, especially in relation to race, ethnicity, and socioeconomic access.

2. Regulatory Landscape on Enrollment Diversity

Regulatory agencies have introduced policies and expectations around inclusive recruitment:

• FDA Diversity Plan Requirement (2022): Requires plans for achieving demographic representation aligned with disease epidemiology
• ICH E8(R1): Advocates for generalizability of results and fair subject selection
• EMA Reflection Paper: Emphasizes underrepresented population inclusion in pivotal trials

Failure to meet diversity expectations can trigger post-marketing requirements or even rejection of marketing applications.

3. How Site Location Drives Enrollment Patterns

Demographic data is highly clustered geographically. Choosing sites in homogenous or affluent regions inadvertently excludes significant portions of the population. Consider the following comparison:

Sponsors targeting enrollment diversity must therefore select site locations where minority populations reside and receive care.

4. Geographic Barriers to Enrollment

Site location can impose the following participation barriers:

• Distance from minority-majority communities
• Lack of public transport to site
• Trial awareness gaps in underserved areas
• Trust and engagement deficits in historically excluded communities
• Lack of culturally or linguistically competent site staff

These must be accounted for during feasibility and startup planning.

5. Using Census and Epidemiologic Data to Guide Site Location

Sponsors can use public datasets to align site planning with diversity goals:

• US Census Data: Demographic distribution by ZIP code
• CDC’s Social Vulnerability Index (SVI): Community risk stratification
• WHO Health Equity Data: Country-level access and outcomes by demographics
• Historic trial enrollment data from ClinicalTrials.gov

Example: A sponsor used SVI data to select six oncology sites in high-vulnerability ZIP codes and saw a 38% increase in non-white enrollment over the prior protocol.

6. Community and Safety-Net Site Partnerships

Instead of relying only on academic medical centers, sponsors should partner with:

• Federally Qualified Health Centers (FQHCs)
• Veterans Affairs (VA) clinics
• Community hospitals and non-profit health systems
• Faith-based health organizations

These locations are embedded in underserved communities and offer trust and access that large academic centers may lack.

7. Decentralized Trials and Mobile Locations

When traditional sites in diverse areas are unavailable, sponsors can deploy:

• Mobile research units for outreach in minority neighborhoods
• Remote visits with home health support
• Telemedicine for screening and consent
• Community center-based pop-up trial sites

These models lower the geographic barrier and bring trials directly to patients.

8. Diversity Feasibility Scorecard

Site feasibility teams should include diversity scoring in their evaluations:

Sites with low scores may be deprioritized unless diversity mitigation plans are established.

Conclusion

Site location is a determinant of diversity—not just an operational variable. Geographic placement determines who hears about the trial, who can access it, and who completes it. Sponsors committed to inclusive trials must strategically plan site networks using census and epidemiological data, community partnerships, decentralized modalities, and targeted outreach in underserved regions. Diversity by design begins with geography, and success depends on embedding these principles into site feasibility from the start.