What Should You Do When the Ideal Research Design Requires More Study Sites Than You Can Manage?

What If Your Research Requires More Study Sites Than You Can Realistically Coordinate?

Your research question calls for evidence from several schools, hospitals, communities, laboratories, or other research settings. Including multiple sites could improve contextual coverage, permit comparisons between settings, or provide enough participants for the planned analysis. However, obtaining permissions, coordinating personnel, standardizing procedures, and monitoring data quality across all those locations exceeds your available resources.

Should you reduce the number of sites, select only the most accessible locations, concentrate on one institution, or abandon the multisite design? If you collect more participants from fewer sites, would that compensate for losing institutional or geographical diversity?

The answer depends on why multiple sites were required in the first place. Reducing the number of locations may be a manageable operational adjustment, or it may remove the very variation the research question was designed to investigate.

Retain the Sites Necessary for the Research Question, Not Simply the Largest Possible Number

How the Number and Selection of Study Sites Affect Research Design

Why Does a Research Study Need Multiple Sites?

Multisite research involves collecting or analyzing data from more than one organizational, geographical, clinical, educational, or other defined setting. The sites may be institutions, facilities, communities, administrative units, or field locations, depending on the research question.

Researchers use multiple sites for different reasons. Some studies require a larger recruitment pool. Others seek to examine whether findings remain consistent across settings or whether contextual characteristics influence outcomes.

These purposes should not be confused. Adding sites to increase the number of participants is not methodologically equivalent to adding sites to investigate institutional variation.

Before changing the design, identify whether sites are needed primarily for:

• Recruitment capacity: Accessing enough eligible participants to achieve the required sample.
• Contextual coverage: Including settings with different characteristics relevant to the research question.
• Between-site comparison: Examining differences among institutions, communities, or service environments.
• Intervention evaluation: Assessing implementation or outcomes across multiple organizational settings.
• Statistical structure: Estimating site-level effects, clustering, or relationships involving contextual characteristics.
• Transferability or generalizability: Providing evidence about the extent to which findings may apply beyond one setting.

A study may have several of these purposes, but their relative importance determines how much site reduction is defensible.

Distinguish the Number of Sites From the Number of Participants

One of the most consequential mistakes in multisite planning is assuming that participants from the same institution provide the same information as participants distributed across several institutions.

Suppose a researcher originally plans to recruit 300 students from ten schools. When coordination becomes difficult, the researcher considers recruiting all 300 students from two schools instead.

The total number of students remains unchanged, but the number of distinct school environments falls substantially.

Students within the same school may share teachers, institutional policies, resources, curriculum structures, and other contextual influences. Their outcomes may therefore be statistically dependent rather than independent observations.

This dependence is commonly described using the intraclass correlation coefficient, or ICC, which represents the degree of similarity among observations within the same cluster under a specified statistical model.

Increasing the number of students within a small number of schools may improve estimation of student-level characteristics within those schools. It does not necessarily provide sufficient information about differences among schools.

When the research question concerns site-level effects, the number of sites can be more consequential than the total number of individual participants.

How Does Site-Level Clustering Affect Sample Size?

In clustered research designs, observations from the same site may be correlated. Treating them as independent can produce misleading standard errors and overly confident conclusions.

For a simplified setting with equally sized clusters, a commonly used design-effect approximation is:

The formula is a planning approximation, not a universal sample-size calculation. Unequal cluster sizes, treatment allocation, covariates, repeated measurements, and the intended statistical model may require different methods.

For cluster-randomized trials and studies examining site-level predictors, the number of clusters and the allocation of clusters across conditions are particularly important. A large number of individuals cannot automatically compensate for too few independent clusters.

When Can You Reduce the Number of Study Sites?

Site reduction may be reasonable when the revised design still provides the variation, recruitment capacity, and statistical information necessary for the primary question.

For example, a descriptive study focused on students within a particular university may not require additional institutions if the target population is explicitly limited to that university.

Likewise, a qualitative study examining a well-defined organizational process may obtain rich and analytically useful evidence from a carefully selected setting. The adequacy of that decision depends on the qualitative approach, research purpose, and information available from participants and observations.

Site reduction becomes more problematic when the study aims to compare institutional policies, estimate between-site variation, or make claims about a diverse population of settings.

Researchers should therefore distinguish between reducing unnecessary geographical coverage and removing settings that are scientifically essential.

How Should You Select Sites When Only a Few Can Be Included?

Selecting sites solely because they are nearby, cooperative, or inexpensive may create important limitations. Convenient sites may differ systematically from inaccessible sites in resources, organizational culture, population characteristics, or willingness to participate.

A defensible site-selection strategy should begin with the intended population of settings and the characteristics relevant to the research question.

For quantitative studies, probability-based selection may be appropriate when the objective is to make design-based inferences about a defined population of sites and a suitable sampling frame is available.

For qualitative and comparative case research, purposive selection may be appropriate when sites are chosen for their theoretical relevance, contrasting characteristics, or capacity to illuminate the phenomenon.

Neither approach guarantees generalizability. The justification must correspond to the intended inference.

A purposively selected set of sites may be valuable for investigating mechanisms or contextual differences, but it should not be presented as a statistically representative sample merely because it contains diverse institutions.

Can One Carefully Selected Site Be Better Than Several Poorly Managed Sites?

Yes, for some research questions. A single-site design may allow consistent measurement, sustained engagement with participants, detailed contextual documentation, and stronger quality assurance.

However, its strengths must be understood in relation to its scope.

A single-site study cannot directly estimate variation among sites. It also cannot establish that the observed relationships would remain unchanged in institutions with different characteristics.

For quantitative research, the implications depend on the sampling design and the intended target population. For qualitative case studies, the emphasis may instead be on analytic explanation and the relationship between the case, its context, and relevant theoretical propositions.

The question is not whether single-site research is inherently inferior. It is whether the research question requires evidence from more than one setting.

Why Does Multisite Research Require More Than Identical Data Collection Forms?

Even when sites use the same questionnaire or data collection template, important differences may remain in recruitment, interpretation of questions, local procedures, outcome definitions, and participant characteristics.

For example, two universities may record student engagement using the same learning management system but differ in whether attendance, assignment submissions, or asynchronous activities are included in particular indicators.

Combining those records without verifying comparability may produce misleading institutional comparisons.

Effective multisite coordination may require:

• A common protocol with clearly defined variables and procedures.
• Site-specific documentation of relevant operational differences.
• Training and competency checks for local research personnel.
• Consistent eligibility and recruitment procedures where required.
• Data dictionaries and rules for resolving inconsistencies.
• Monitoring of missing data, protocol deviations, and measurement quality.
• Appropriate arrangements for privacy, data access, and secure transfer.

Standardization does not necessarily mean eliminating every local difference. In some studies, contextual variation is part of what researchers intend to investigate. The objective is to distinguish meaningful variation from preventable inconsistencies.

Can Local Collaborators Make a Larger Multisite Study Feasible?

Qualified local collaborators may reduce the burden of coordinating recruitment, data collection, participant communication, and institutional procedures.

However, decentralizing research activities does not eliminate the need for central methodological oversight.

Collaborators should understand the protocol, their responsibilities, the required documentation, and the procedures for reporting problems. Agreements may also be needed concerning data access, authorship, intellectual contributions, and institutional obligations.

Adding sites through informal arrangements without sufficient training or monitoring can increase heterogeneity in data quality.

Researchers should therefore evaluate not only how many sites can be recruited but how many can be managed to the required standard.

When Does Reducing Sites Fundamentally Change the Research Question?

Some research questions depend directly on variation among settings.

A study asking whether an intervention performs differently in urban and rural schools requires an appropriate basis for comparing those contexts. Removing one category of school would eliminate the intended comparison.

Similarly, a study examining how institutional policies influence student outcomes cannot adequately estimate institutional variation from one institution alone.

In such situations, the researcher may need to narrow the question from a cross-institutional explanation to a within-institution investigation.

The revised question may still be worthwhile, but its claims must reflect the reduced scope.

When Should You Postpone a Multisite Study?

Postponement may be appropriate when the intended inference requires a minimum number or distribution of sites that cannot be obtained or managed.

This may occur in cluster-randomized trials, studies estimating contextual effects, or comparative investigations in which essential categories of settings are unavailable.

Before postponing, consider whether a narrower study, a preliminary feasibility investigation, or a different sampling strategy can address a distinct and scientifically meaningful question.

Reducing a Ten-School Study to Three Schools

The researcher initially proposes recruiting 100 students from each of the three accessible schools to preserve the total sample of 300.

Although this retains the number of students, it reduces the number of school contexts from ten to three. It also changes the clustering structure and limits the information available for estimating between-school variation.

The revised design may remain useful if its student-level analyses are appropriate and the researcher accounts for the clustered structure. However, only three schools would generally provide a weak basis for complex statistical estimation of school-level variation or contextual effects.

The researcher should not interpret the unchanged student sample size as evidence that the original multisite objectives remain achievable.

If the central scientific contribution depends specifically on comparing institutional contexts, postponement or a larger collaborative study may be more defensible than proceeding with three sites.

Common Misconceptions About Reducing Study Sites

How to Decide Whether Fewer Study Sites Are Sufficient

Begin by identifying the scientific purpose of including multiple sites. Then determine which locations, site characteristics, and independent clusters are necessary for the intended comparisons and analyses.

Do not make the decision using site count alone. The adequacy of a revised design depends on the relationship between the remaining sites and the research question.

For thesis and dissertation research, consider whether a multisite design is appropriate within the academic and supervisory constraints. Institutional permissions and local coordination may create dependencies that are difficult for an individual researcher to control.

If the revised design requires substantially fewer locations, assess whether a smaller, carefully implemented study would be preferable to a larger but inconsistently managed project.

When the available sites cannot support the original question, the decision may involve simplifying the design, narrowing the research question, or postponing the study.

Document the rationale for the final number and selection of sites, the expected consequences for sampling and analysis, and the limits of the resulting conclusions. Site reduction should be a justified methodological decision, not an unexplained consequence of unsuccessful coordination.

Before Reducing the Number of Study Sites

Frequently Asked Questions About Study Site Limitations

The Right Number of Sites Depends on What the Study Must Establish

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