Are All Births Counted? Uncovering Hidden Underreporting with Capture-Recapture
"A Deep Dive into Vital Statistics and Population Estimates."
Ensuring accurate counts of vital events like live births is critical for effective public health planning and resource allocation. However, underreporting—when births go unrecorded—presents a persistent challenge in vital statistics. This can lead to skewed fertility and mortality rates, hindering evidence-based policymaking.
Traditional methods for calculating fertility and child mortality rates rely on complete and accurate birth and death records. When these records are incomplete, the resulting statistics can be misleading. This is where innovative techniques like capture-recapture come into play, offering a way to estimate the true number of events, even when some go unrecorded.
Capture-recapture, initially used in ecology to estimate animal populations, has found valuable applications in epidemiology and demography. This method leverages the overlap between different data sources to estimate the total population size, providing a more complete picture than any single source alone. This article delves into how capture-recapture can be used to estimate underreporting of live births, using a case study from Sergipe, Northeastern Brazil.
Birth Data Around the World
In the United States, the National Center for Health Statistics reported 3,628,934 births in 2024, yielding a birth rate of 10.7 per 1,000 population and a fertility rate of 53.8 per 1,000 women aged 15–44. Among these births, 75.5% of mothers initiated prenatal care in the first trimester, 10.41% were born preterm, and 32.4% were delivered via cesarean. California maintains its own comprehensive birth data dashboard covering 2000–2024, enabling detailed state- and county-level analyses. Meanwhile, Brazil's IBGE has launched a dedicated data dashboard specifically to visualize sub-registration and underreporting of births and deaths, acknowledging that official counts may not capture the full picture.
Measuring Registration Completeness
Civil registration and vital statistics systems are gaining new momentum as demand grows for accountability, equity, and rights-based approaches to health and development challenges. Multiple technical guidance documents outline methods for assessing birth registration completeness, including approaches from UNFPA and Vital Strategies that describe principles, data needs, and methodologies applicable at local, district, and national levels. However, the accuracy of birth certificate data varies significantly by risk factors—a 2006 study in the American Journal of Obstetrics and Gynecology found that underreporting of birth certificate data elements differs by maternal characteristics, particularly English-language proficiency, transfer status, and birth outcomes. These limitations mean that even registered births may contain incomplete or inaccurate information, complicating efforts to measure true registration coverage.
The Birth Certificate's Evolution
Birth records have evolved over centuries from church registers to government-administered systems, reflecting a fundamental shift in who controls the documentation of identity. In the United States, reformers pushed state by state to adopt standardized birth certificates before federalizing the new standard, and by 1940 the birth certificate had become the primary document for legitimizing age—though retroactive registration was still permitted, meaning the certificate itself was not absolutely foolproof. Research examining childhood exposure to birth registration laws across US states in the early twentieth century has found measurable effects on old-age longevity, suggesting that the act of registering births carries consequences beyond mere documentation. This historical arc reveals that birth registration systems have long grappled with completeness challenges, even as they became institutionalized.
How Capture-Recapture Unveils Hidden Births
The capture-recapture method works by comparing two or more independent data sources, or “lists,” that record the same events. In the context of live births, these lists could be:
- The Live Birth Information System (SINASC): A national database maintained by the Ministry of Health.
- Civil Registry: Records from the Brazilian Institute of Geography and Statistics (IBGE).
Global Progress and Persistent Gaps
A 2023 global and regional assessment examined the timing of birth registration using all available data for children under five, emphasizing that registration within the first year of life is essential for children to receive full legal benefits and for fertility statistics to be useful for policy. A literature review published in Global Health Action identified facility-based initiatives that increased birth registration rates, while in-depth interviews with global stakeholders revealed that health promotion within communities also boosted demand for registration. Research evaluating COVID-19's impact on birth registration in a predominantly indigenous population in Chiapas, Mexico, highlighted significant underreporting challenges that persisted during the pandemic. These studies collectively demonstrate that while progress is being made, significant registration gaps remain across diverse contexts.
System Failures and Exclusions
The United States maternal mortality reporting system has been criticized for coding failures, where every death with a pregnancy or postpartum checkbox marked is coded to maternal causes regardless of what is written in the cause-of-death section, except for external injury causes. The Global Inventory of birth registration reveals systemic exclusion affecting migrants' children in particular, with the Dominican Republic receiving the highest number of UN human rights observations on the issue due to its treatment of descendants of Haitian migrants. Legal challenges in birth registration processes create barriers for marginalized populations, with complex frameworks that often produce conflicts and inequities. Research published in the American Journal of Public Health has hypothesized a strong relationship between underreporting of birth certificate data and infant death, since missing data tends to cluster among groups at highest risk for perinatal problems.
Cross-Checking Registration Data
A comparative study examining birth certificates alongside hospital-based birth records in Los Angeles County and Orange County, California, investigated underreporting of adverse pregnancy outcomes by cross-referencing two independent data sources. The research specifically focused on whether underreporting rates varied according to socioeconomic status, recognizing that differential completeness could skew public health analyses. Additionally, researchers have evaluated how reliable self-reported estimates of birth registration completeness are by comparing them against UNICEF and UN World Population Division calculations using the Global Burden of Disease Study. These methodological comparisons are essential for understanding the true scope of registration gaps and for validating the data that inform policy decisions.
Why Accurate Birth Counts Matter
The study in Sergipe, Brazil, revealed a 19.3% underreporting of live births during the study period, highlighting the importance of using methods like capture-recapture to improve vital statistics. By applying capture-recapture, public health officials can gain a more accurate understanding of birth rates and population dynamics, even in regions with incomplete registration systems.
The Infant Mortality Connection
Research published in the American Journal of Public Health has established that incomplete birth certificates function as a risk marker for infant mortality. The study hypothesized—and found evidence supporting—a strong relationship between underreporting of birth certificate data and infant death, since missing birth certificate data tends to be associated with groups already at highest risk for perinatal problems. This finding carries profound implications: the very populations most vulnerable to poor birth outcomes are also the least likely to have complete registration data. The result is a systemic blind spot where the children who most need public health interventions are the least visible in the data systems designed to track and support them.
The Road to Universal Registration
UNICEF reported in December 2024 that while global birth registration rates have increased from 75% in 2019 to 77%, approximately 150 million children under five still remain unregistered and invisible to government systems. The Sustainable Development Goals include a dedicated target (16.9) under Goal 16 to provide legal identity for all, including birth registration, by 2030, complemented by target 17.9 calling for support in achieving this aim. Over 500 million children under five—close to 8 in 10—have had their births registered in recent years, reflecting notable strides in securing legal identity worldwide. However, the persistent gap of 150 million unregistered children underscores the magnitude of the challenge remaining.
Digital Tools and Regional Disparities
The use of digital technologies for birth registration raises human rights concerns, particularly for children in vulnerable or marginalized conditions, where such systems may perpetuate colonial extractive models and practices rather than empower communities. Despite these challenges, some countries have achieved remarkable gains—in sub-Saharan Africa, Botswana has reached universal birth registration, while Côte d'Ivoire has surpassed 90% coverage. Rwanda, Sierra Leone, Tanzania, and other nations have also demonstrated sustained improvement over the past decade, showing that progress is possible even in resource-constrained settings. These regional disparities highlight that while technology and policy reforms can drive improvements, equity in access remains a critical systemic challenge.
Digital Identity for Displaced Populations
Digital identity and birth registration mechanisms with mutual recognition across countries can provide critical benefits for refugees and migrant communities. For the most vulnerable and marginalized populations, such systems can facilitate access to services and support in host communities, humanitarian aid, employment opportunities, and sustainable livelihoods. The ability to carry recognized documentation across borders addresses a fundamental gap in protection for displaced children who might otherwise remain legally invisible. This human-centered perspective emphasizes that birth registration is not merely a statistical exercise but a gateway to rights, services, and dignity for the world's most vulnerable children.
While the study faced challenges such as data quality issues and meeting the assumptions of the capture-recapture method, it demonstrated the potential of this technique for estimating underreporting at smaller geographic scales. Further research and improvements in data collection can enhance the accuracy and reliability of these estimates.
Ultimately, more accurate birth counts lead to better-informed decisions about healthcare resource allocation, maternal and child health programs, and overall public health planning. By embracing innovative statistical methods, we can move closer to ensuring that every birth is counted and every individual is given the opportunity to thrive.