Best Free Sources of Health Statistics

By Kevin Fernando · Oct 9, 2026 · 8 min read

No single source is universally best. CDC WONDER serves U.S. epidemiology, WHO Global Health Observatory enables international comparison, ClinicalTrials.gov provides trial data, PubMed Central offers peer-reviewed literature, and national health surveys like NHANES provide population-level measurements. Match your source to your specific research question.

Health research requires different data depending on the question. Studying disease patterns in one country demands different tools than comparing outcomes across nations. Evaluating a clinical trial requires access to registrations and results, while synthesizing evidence requires peer-reviewed literature. Understanding what each major free source contains, and what it does not, lets researchers choose the right tool rather than settling for what is easiest to find.

This article maps the major free sources to specific research needs. Each source excels at particular questions and has clear limitations. The goal is not to rank them universally but to show which one fits which work.

What you're choosing between

Health statistics come in distinct forms, and each source specializes in one or two. Disease registries track specific conditions or causes of death at the population level. International databases aggregate comparable indicators across countries. Clinical trial registries collect information about studies before, during, and after they run. Peer-reviewed literature contains published research findings, methods, and analysis. Population health surveys measure health status, risk factors, and health behaviors in representative samples of people.

Each category answers different questions. If you need to know how many deaths from a specific cause occurred in a U.S. county last year, you need a disease registry. If you need to compare life expectancy across 50 countries, you need an international database. If you need to find whether a trial for a specific drug has been registered, you need a trial registry. If you need to read the statistical methods used in a study, you need the published paper. If you need to know the prevalence of a health condition in the general population, you need a survey. A researcher often needs more than one.

How to evaluate a health statistics source

Five criteria separate useful sources from those that waste time. Data currency matters: a mortality database updated annually is more useful than one frozen five years ago. Geographic scope determines whether you can answer your question: a U.S.-only source cannot support international comparison. Methodology transparency lets you judge whether the data answers your question or answers a different one. Granularity, the level of detail available, determines what you can analyze: county-level data supports more specific analysis than state-level data. Ease of access affects whether you can actually retrieve what you need without specialized software or institutional credentials.

No source excels on all five. A database with excellent currency may have limited geographic scope. A source with rich granularity may require technical skill to access. Understanding these trade-offs prevents choosing a source that looks good but cannot answer your specific question.

CDC WONDER (United States disease and mortality data)

CDC WONDER (Wide-ranging Online Data for Epidemiologic Research) is the U.S. federal government's query system for epidemiological data. It contains multiple categories of data: mortality by cause, cancer incidence and mortality, births, AIDS, sexually transmitted disease morbidity, and environmental health data including heat wave days.

Mortality data span decades. The Compressed Mortality File covers 1968 through 1998, and the Multiple Cause of Death file covers 1999 through 2017. Cancer statistics are available from 1999 forward. Natality data are derived from U.S. birth certificates at the county level. All data are available at county, state, and national geographic levels, making WONDER useful for highly specific geographic analysis.

The system's strength is granularity and historical depth for U.S. epidemiology. Its limitations are clear: it contains only U.S. data, it does not include unpublished research or trial data, and it focuses on mortality and specific reportable conditions rather than the full spectrum of health outcomes. Researchers outside the United States cannot use it for their own countries' data.

WHO Global Health Observatory (international health indicators)

The WHO Global Health Observatory is the primary source for comparing health indicators across countries. It contains over 1000 indicators for 194 Member States [F5, F22]. Core categories include demographic and socioeconomic statistics, health service coverage, health systems resources, inequities in healthcare and health outcomes, and mortality and burden of disease and risk factors.

The database has been maintained since 2009, though historic data are available from the early 1930s for certain datasets. This depth allows researchers to track long-term trends in countries where data collection has been consistent.

The Observatory's strength is international scope and standardized indicators that enable valid comparison across countries. Its limitations are that it aggregates data at the national level (no subnational granularity), the data lag behind real time, and the indicators available vary by country depending on what each nation reports to WHO. Researchers needing current data or subnational detail must look elsewhere.

ClinicalTrials.gov (clinical trial registry and results)

ClinicalTrials.gov is the world's largest clinical trial registry, launched in 2000 by the NIH National Library of Medicine. It contains trial registrations (metadata about planned studies) and results submissions (summary data from completed trials). As of September 2010, it held 79,413 registry records and 2,178 results records, with approximately 330 new and 2,000 revised registrations received each week.

The registry captures trial design, eligibility criteria, sponsor information, and outcomes. Results submissions include primary and secondary outcome data. However, quality varies: 20% of results records reported more than two primary outcome measures and 5% reported more than five, suggesting inconsistent outcome reporting. Additionally, 24% of sampled trials reported results for 90% or fewer of their enrolled participants, indicating incomplete follow-up reporting.

The strength of ClinicalTrials.gov is that it provides a searchable index of trials and a growing repository of results without requiring subscription access. The limitations are significant: it contains trial summaries, not full published papers; results reporting is voluntary and incomplete; and the database does not include trials that were never registered. Researchers need the published paper to understand methods and full statistical analysis.

PubMed Central and MEDLINE (peer-reviewed literature)

MEDLINE is the U.S. National Library of Medicine's bibliographic database of peer-reviewed biomedical literature. It indexes approximately 5,600 journals published worldwide, with records starting in the early 1800s. PubMed Central is the free full-text archive of MEDLINE articles. MEDLINE Complete, the full-text version, provides full text for over 2,400 of the indexed journals. Of the 2,500+ full-text journals available in MEDLINE Complete, more than 1,350 titles are not found with full text in any version of Academic Search, Health Source or Biomedical Reference Collection.

These sources contain published research: study design, methods, statistical analysis, and findings. They do not contain raw epidemiological data, trial registrations, or unpublished research. They are the appropriate source when you need to understand how a study was conducted or to synthesize findings across multiple published studies.

The strength is comprehensive coverage of published evidence and methodological detail. The limitation is that published research represents a filtered subset of all research conducted, trials with negative results are less likely to be published, and accessing the full text of all journals requires either institutional subscription or use of the free PubMed Central subset.

National Health Statistics Systems (country-specific surveys)

Most developed nations conduct large-scale population health surveys that measure health status, health behaviors, and health risk factors in representative samples. In the United States, the primary example is the National Health and Nutrition Examination Survey (NHANES). NHANES examines a nationally representative sample of about 5,000 persons each year across 15 counties visited each year. The survey became continuous in 1999.

NHANES collects three types of data. The interview component includes demographic, socioeconomic, dietary, and health-related questions. The examination component consists of medical, dental, and physiological measurements and laboratory tests. A curated dataset merged 614 separate NHANES files, harmonizing unrestricted data across NHANES III (1988-1994) and the Continuous program (1999-2018), totaling 134,310 participants and 4,740 variables.

These surveys are the primary source for population-level health outcome data and prevalence estimates. Their strength is that they measure actual health status in representative populations rather than relying on reported diagnoses or administrative records. Their limitation is that they are country-specific, each nation runs its own survey with its own design and variables, so international comparison requires accessing each country's survey separately and understanding how their methodologies differ.

Which source fits which research question

Matching your research question to the right source saves time and prevents dead ends. The sections below show which source answers which type of question.

Finding disease prevalence in a specific country

Prevalence, the proportion of a population with a condition at a specific time, requires population-level data. For the United States, NHANES is the primary source for prevalence of health conditions, risk factors, and health behaviors in the general population. For other countries, the relevant national health survey varies: the UK has the Health Survey for England, Australia has the Australian Health Survey, and so on. CDC WONDER is not appropriate for prevalence because it contains only deaths and specific reportable conditions, not the full spectrum of health status in the population. If you need prevalence in multiple countries, you must access each country's survey separately rather than using a single international database.

Comparing health outcomes across multiple countries

International comparison requires standardized indicators measured the same way across countries. WHO Global Health Observatory is designed for this purpose. It contains comparable indicators for 194 Member States, enabling you to see how life expectancy, mortality rates, health service coverage, or other metrics differ across nations. CDC WONDER cannot be used for this because it contains only U.S. data. National health surveys cannot be used because each country's survey uses different methods and variables. If the specific indicator you need is not in the Observatory, you may need to access individual country surveys and harmonize the data yourself, which requires understanding methodological differences.

Accessing clinical trial data and results

ClinicalTrials.gov is the starting point for finding trials and their results. Search by condition, drug, or sponsor to find trials that match your criteria. Results submissions provide summary outcome data for completed trials. However, results on ClinicalTrials.gov are summaries, not full papers. To understand the trial's methods, statistical analysis, and full results, you need the published paper. Search PubMed Central or MEDLINE using the trial's NCT number (the unique identifier assigned by ClinicalTrials.gov) to find the published report.

Locating published epidemiological studies

PubMed Central and MEDLINE are the appropriate sources for finding published research. Search by topic, author, or journal to find studies relevant to your question. MEDLINE indexes approximately 5,600 journals published worldwide. PubMed Central provides free full text for many articles; for others, you may need institutional access or to contact the author. If you are looking for a specific study you have already identified, search by title or author. If you are synthesizing evidence on a topic, search by subject terms and review multiple papers to understand the state of the evidence.

Do this automatically

Manually compiling health statistics from disease registries, international databases, and clinical trial registries across multiple geographic regions and update cycles requires hours of cross-referencing and verification per dataset, multiplied across the dozens of sources a researcher might need to consult. Software can consolidate these disparate sources into a single query interface, eliminating the manual aggregation work that currently consumes research time. Academia research surveys the literature, extracts the findings and methods described above, and attaches a citation to every claim it reports, across as many subjects as you need, with Mimir attaching a citation to every figure. It will not make the decision for you. It gathers and cites the evidence; the judgment stays yours, and deliberately so. Every plan includes it, including the free one.

Start your first report and run it on something you already know well.

This article is general information and research commentary. It is not professional advice, and it does not account for your particular circumstances.