Should You Search Globally Before Focusing on Local Evidence?

Should the literature search start globally or locally?

If your research problem is rooted in a particular country, province, city, institution, or community, starting with local studies can feel intuitive. After all, evidence produced nearby may appear more relevant to the population and setting you actually care about.

But beginning and ending with local evidence can create another problem. You may overlook a much larger body of research that has already examined the phenomenon, tested explanations, evaluated interventions, or identified conditions under which findings change.

The real issue is therefore not whether global evidence is better than local evidence. It is what each type of evidence can tell you, and in what sequence searching them is most informative.

Usually, establish the broader evidence before narrowing your interpretation

Global and local evidence often do different intellectual work

“Global” does not mean universally applicable

Global evidence can be understood as the broader body of relevant evidence available across settings rather than evidence from one particular locality. It may include individual studies from several countries, multicountry research, systematic reviews, evidence syntheses, and other research relevant to the question.

The term does not imply that the findings apply everywhere. Every study was conducted somewhere, with particular populations, institutions, resources, cultures, policies, and historical conditions. Evidence gathered across many settings can provide a broader basis for understanding a phenomenon, but its applicability to a particular setting still requires judgment.

Why start by understanding the broader evidence base?

A broad search can show what researchers already know before geography is used to narrow the field. This matters because conclusions based only on a geographically selected subset of studies can differ from conclusions based on the full relevant evidence base.

In evidence-informed policymaking, Lavis and colleagues argue that the best available global evidence is generally the appropriate starting point for judgments about the effects of policies and programmes. They caution that selecting only observations presumed to be more locally relevant can be misleading when those observations are considered without the broader evidence.

The same reasoning can be useful beyond policy research. A broader search may reveal established theories, competing explanations, commonly used measures, previous interventions, methodological problems, contradictory findings, and variables that later become important when you examine the local literature.

Local evidence answers questions that global evidence may not

Broader evidence does not make local evidence redundant. Local evidence can tell you about conditions that international studies cannot simply supply: the magnitude of a problem in the setting, institutional arrangements, available resources, implementation constraints, population characteristics, costs, stakeholder experiences, and other contextual factors.

Lewin and colleagues distinguish these roles clearly in their work on evidence-informed policymaking. They describe global evidence as a useful starting point for understanding effects and possible approaches, while local evidence is needed for many judgments about what should actually be done in a particular setting.

The sequence is conceptual, not necessarily chronological

You do not have to finish every international search before typing the name of your country into a database. Literature searching rarely behaves that neatly.

You might find a local paper first, discover useful terminology from it, search internationally, identify an important mechanism, and then return to the local literature with a better search vocabulary. That iterative movement is perfectly reasonable.

What matters is that your final understanding does not begin from the assumption that only geographically close studies are relevant. When the research question itself is highly local, a layered search across broader and local sources can help prevent geography from becoming an unnecessarily restrictive filter.

Ask whether context could plausibly change the answer

The balance between global and local evidence depends heavily on the question. Some findings may transfer reasonably well across settings. Others depend strongly on context.

Consider what could differ between the settings represented in the broader literature and your own. Relevant differences might involve population characteristics, infrastructure, institutional rules, implementation capacity, available technology, economic conditions, culture, language, baseline risk, environmental conditions, or the way an intervention is delivered.

Research on transferring evidence-based interventions across settings similarly emphasizes the need to examine local contextual evidence when populations or environments differ in ways that could affect implementation or outcomes.

Do not confuse geographic proximity with evidential strength

A study conducted in your own city is not automatically more trustworthy than a well-designed study conducted elsewhere. Locality affects relevance, not methodological quality.

Conversely, methodological strength does not eliminate questions of applicability. A rigorous study conducted under substantially different conditions may provide strong evidence about what happened there while leaving uncertainty about what would happen here.

These are separate judgments. One concerns how much confidence you can place in the study's findings. The other concerns how well those findings apply to the setting relevant to your question.

Global and local findings may legitimately disagree

Suppose a systematic review suggests that an intervention is generally effective, while local studies show weaker results. The appropriate response is not automatically to discard either evidence source.

The difference may reflect methodological weaknesses, random variation, population differences, implementation problems, resource constraints, or genuine effect modification. Lewin and colleagues recommend identifying and discussing discrepancies between global and local evidence rather than silently privileging one source.

How broader evidence can change the way you interpret a local literature

The broader literature did not answer the local question on its own. It made the local evidence more interpretable and helped the researcher ask a more precise question.

Common mistakes when balancing global and local evidence

Let the research question determine how global and local evidence are combined

Instead of asking which evidence should dominate, ask what judgment you are trying to make.

The amount of local evidence required therefore depends on what is at stake in transferring the broader finding. A question about a relatively context-insensitive relationship may require less local verification than one involving institutional implementation, culturally dependent behavior, resource-intensive interventions, or populations substantially different from those represented in existing research.

This is also why the question of whether strong international evidence can compensate for limited local evidence cannot be answered simply by comparing the number of studies in each group.

Before narrowing from broader evidence to the local literature

Questions about searching global and local evidence

Start broad enough to know the evidence, then get local enough to judge its relevance

How to Cite This Guide

This guide is intended to be read, shared, and used in research, teaching, and academic work. If you draw on its ideas, explanations, or other content, please acknowledge the source by citing the guide. Doing so gives appropriate credit and helps your readers locate the original resource.