- When traditional methods are not enough, methodological innovation helps make the invisible visible.
- There is no single method: each population and each context require different research strategies.
- Trust and ethics are as important as the methodology to produce quality evidence.
Statistics are the starting point for many public decisions. They make it possible to estimate how many people need a service, identify where the biggest gaps are concentrated, and assess whether an intervention is generating the expected results.
But what happens when some of the populations these decisions seek to serve are not represented in the statistics? When they remain invisible in the data, they can also be left out of the design, implementation, and evaluation of public policies.
Although they are part of society, many populations remain invisible in official statistics across Latin America and the Caribbean. People in an irregular migratory situation or on the street, deprived of liberty, survivors of violence, users of illegal drugs or living with HIV are often left out of conventional censuses and surveys due to stigmatization, discrimination, high mobility or lack of administrative records. This absence of data makes it difficult to understand their needs, design appropriate responses, and allocate resources effectively, limiting the ability of public policies to respond to their realities.
Precisely to meet this challenge, the Inter-American Development Bank (IDB) published the technical note Uncovering the Hidden: Innovative Methods for Data Collection from Hard-to-Reach Populations. The publication reviews the main methods available to study these populations and collects the experiences of specialists with extensive experience in field research. Rather than presenting a set of techniques, the publication offers practical guidance to strengthen the production of evidence and improve decision-making.
For decades, censuses and household surveys have been the main sources of information for understanding the living conditions of populations. However, these instruments rely on certain assumptions that are not always met: that people can be identified through records or sampling frames and that they are willing to participate in data collection.
Hard-to-reach populations face conditions that defy these assumptions. Some do not have official records that allow them to be located; others fear being discriminated against or facing possible legal and social consequences. Many experience situations of exclusion, distrust of institutions, high territorial mobility or live in contexts where participating in a survey can be risky.
In the absence of appropriate sampling frames, different disciplines have developed innovative methods. Many of these approaches initially emerged in the field of public health and, over time, were adapted to study a wide variety of social phenomena.
Some methods take advantage of the social networks of the participants; others identify the places where these populations usually gather; and others make it possible to estimate the size of populations for which there are no official records or to better understand their experiences and interaction with public services.
Methods for Studying Hard-to-Reach Populations | |
| Method | What is it used for? |
| Snowball Sampling | Reaching individuals through the trusted networks of participants who are already involved in the study. |
| Targeted Sampling | Strategically identifying areas and subgroups where the population is concentrated. |
| Capture-Recapture | Estimating the size of a population without official records by comparing individuals identified across two or more rounds of data collection. |
| Time-Location Sampling (TLS) | Recruiting participants at locations and times where they typically gather. |
| Respondent-Driven Sampling (RDS) | Producing more robust estimates by using social networks and statistical weighting. |
| Mystery Shopping | Assessing service quality from the perspective of service users. |
| Vignette studies | Exploring perceptions and decision-making in sensitive situations without directly asking about personal experiences. |
Source: Uncovering the Hidden: Innovative Methods for Collecting Data from Hard-to-Access Populations.
The main lesson is that there is no single method. The choice depends on:
- The characteristics of the population and the context.
- The research question.
- The type of evidence that is sought to be generated.
While some approaches aim to produce robust estimates, others allow us to understand experiences, barriers, or behaviors that are difficult to capture through conventional instruments.
Methodological innovation, therefore, is not about finding a perfect technique, but about selecting the most appropriate strategy to respond to each research challenge and generate useful evidence for decision-making.
Methodology by itself,is not enough. One of the main contributions of the publication arises from the interviews conducted with 16 specialists with extensive experience in fieldwork with populations that are difficult to access. Their experiences show that generating quality evidence requires both methodological rigor and the ability to build trusting relationships with the people and communities involved.
The interviews highlight several practices that strengthen both the quality of the information collected and the experience of those involved in the research:
- Incorporate members of the communities themselves into the fieldwork team.
- Work together with local organizations that already have trusted links.
- Use respectful and culturally relevant language.
- Ensure confidentiality throughout the process.
- Create safe spaces for participation.
These recommendations can not only encourage greater participation, but also contribute to collecting more complete, accurate, and relevant information for decision-making.
As one of the interviewees summarized:
Producing evidence with hidden populations is not only a technical challenge, it is an ethical commitment"
That phrase sums up one of the main messages of the document. Researching hard-to-reach populations requires balancing scientific rigor with the responsibility to protect participants and minimize the risks of discrimination, stigmatization, or situations that may increase their vulnerability.
Statistics are a fundamental source for understanding the realities that public policies seek to address. When certain groups are left out of the data, they can also be left out of the solutions. Therefore, producing reliable evidence on hard-to-reach populations is key to designing more effective policies and better targeting public resources.
The technical note Uncovering the Hidden: Innovative Methods for Data Collection from Hard-to-Reach Populations provides practical guidance for advancing this goal. In addition to reviewing seven widely used instruments for studying these populations, it draws on the lessons of specialists with field experience and translates them into concrete recommendations for researchers, governments, and organizations.
The underlying message is clear: producing better evidence is not just about applying and replicating more sophisticated techniques. It also involves understanding which populations are not being adequately represented in the data, adapting methods to each context, and building research processes based on trust, respect, and ethics.
Would you like to learn more about the seven methods, their applications, and the recommendations for investigating hard-to-reach populations?
