Access: The ability to get needed medical care and services.
Affordable Care Act (ACA): The health care reform law enacted in March 2010 in two parts: the Patient Protection and Affordable Care Act and the Health Care and Education Reconciliation Act.1
Age Adjustment: A process of direct standardization designed to account for age as a confounding variable.
Age-Specific Mortality Rates: The number of deaths of residents of a specified age in a specified geographic area, divided by the population in a given time period.2
Agency for Healthcare Research and Quality (AHRQ): An operating division of the U.S. Department of Health and Human Services (HHS) that supports research that helps people make better, more informed decisions and improve the quality of health care services in the U.S.
American FactFinder: An interactive online application from the U.S. Census Bureau that provides statistics from many Census Bureau data sources. The Census Bureau is a bureau of the U.S. Department of Commerce.
Behavioral Risk Factor Surveillance System (BRFSS): A system of telephone surveys about health care, health risks, chronic conditions, and use of preventive services from the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS). The BRFSS collects data in all 50 states, Washington, D.C., and three U.S. territories. It is the largest continuously conducted health survey system in the world.3
Bias: A systematic error in study design, subject recruitment, data collection, or analysis that results in a mistaken estimate of the true population parameter. There are many types of bias that can impact research, some examples include selection bias, which occurs when the procedures used to select subjects produce a result that is different from what would have been obtained if all members of the target population were included in the study; information bias, which refers to a "systematic error due to inaccurate measurement or classification of disease, exposure, or other variables"4 and recall bias, which occurs when study participants do not remember the information they report accurately or completely.
Causation: Two variables are causally related if changes in the value of one cause the other to change.5 Probabilistic causation means that the relationship between the independent variable and the dependent variable (X and Y) are such that X increases the probability of Y when all else is equal.
CDC WONDER (Wide-ranging Online Data for Epidemiologic Research): A system of searchable databases with access to a wide array of public health indicators, including measures of chronic and communicable disease, environmental health, disease and injury prevention, and occupational health. CDC WONDER is a resource of the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS).
Centers for Disease Control and Prevention (CDC): The primary federal public health agency in the U.S., offering many data resources and tools to state and local health departments and the general public. CDC is an operating division of the U.S. Department of Health and Human Services (HHS).
Centers for Medicare & Medicaid Services (CMS): The federal agency that administers Medicare and collaborates with states to administer Medicaid, the Children’s Health Insurance Program (CHIP), and the Health Insurance Marketplace. CMS is an operating division of the U.S. Department of Health and Human Services (HHS).
Chronic Conditions Public Use Files (PUF): A resource of the Centers for Medicare & Medicaid Services (CMS), an operating division of the U.S. Department of Health and Human Services (HHS). Chronic Conditions PUFs contain information from Medicare claims. Each record is a profile defined by the characteristics of Medicare beneficiaries.6
Claim: A request for payment for services and benefits received.7
Claims Data: Also known as administrative data, is information collected on millions of doctors’ appointments, bills, insurance, and other patient-provider communications directly from notes made by the health care provider, and happens at the time patient sees the doctor.
CMS Data Navigator: Lets users search across all Centers for Medicare and Medicaid Services (CMS) programs using a menu-driven search application. Users can specify a particular type of data, or search for all available data types. CMS is an operating division of the U.S. Department of Health and Human Services (HHS).
CMS Statistics: A yearly reference booklet that people can download on the Centers for Medicare and Medicaid Services (CMS) website. It has summary information about health care expenses and use. CMS is an operating division of the U.S. Department of Health and Human Services (HHS).
Confidence Interval: Describes the amount of uncertainty associated with a sampling method. Confidence intervals are usually reported to help explain how reliable, or precise, a result is.
Confounding Variable (or Confounder): A variables or variable that are related to both the dependent and independent variable. Confounding variables affect/distort the relationship between independent and dependent variables in a study.
Correlation: Also referred to as association is a liner relationship between two variables. Two variables can be correlated without having a causal relationship, and two variables can have a causal relationship and yet be uncorrelated.8
Covariation of Cause and Effect: Means that there is an established relationship between the two variables regardless of causation. Covariation of cause and effect is a part of the process of determining causation.
Data Disaggregation: Separating data into measures or variables of interest.
Dartmouth Atlas of Healthcare: A website created in 1993 as a study of health care markets which has data tables, maps, publications, and other resources. The data focus on variations in health care resources and how they are used in different geographic regions. The Dartmouth Atlas of Healthcare is a resource of the Dartmouth Institute for Health Policy and Clinical Practice at Dartmouth University in New Hampshire.
Degrees of Freedom: A common statistical term, especially when determining statistical significance, and they represent the number of values that are allowed to vary when estimating the statistic.9
Dependent Variable(s): The response or factors that are measured during a study. The dependent variable responds to the independent variable.
Direct Standardization: An adjustment procedure used during data analysis designed to remove an extraneous source of variation to allow for comparison between groups with unlike characteristics.10 In direct adjustment, a common structured population is used as standard so as to compare two populations.11
Disease Registries: A type of public health surveillance that allow the collection, storage, retrieval, analysis, and dissemination of information about people with a specific disease or condition.
Electronic Health Records (EHRs): Electronic versions of patients’ health information including medical history, diagnoses, medications, and other information that can be shared among providers for collaborative treatment, quality improvement, health planning, and clinical research.
Evidence-based Medicine (EBM): "The conscientious, explicit, judicious and reasonable use of modern, best evidence in making decisions about the care of individual patients."12
Evidence-informed Policymaking: "An approach to policy decisions that is intended to ensure that decision making is well-informed by the best available research evidence."13
FastStats: A website within the website of the National Center for Health Statistics’ (NCHS) of the Centers for Disease Control and Prevention (CDC) that offers quick and easy access to statistics on specific health topics, from diseases and conditions to health care and insurance. The CDC is an operating division of the U.S. Department of Health and Human Services (HHS).
Global Health Facts: From the Kaiser Family Foundation provides data on more than 100 indicators on HIV/AIDS, tuberculosis, malaria and other key measures of health and socioeconomic status, organized by country. The Kaiser Family Foundation is a non-profit foundation that runs programs in policy analysis, journalism, and communications.
Global Health Observatory (GHO) Data Repository: A data repository that contains a list of global indicators on priority health topics, including morbidity and mortality estimates, child health and nutrition, immunization, health systems, environmental health, HIV/AIDS, tuberculosis, and malaria, and more. The GHO Data Repository is a resource of the World Health Organization (WHO), an intergovernmental organization in the United Nations (UN) system.
Health Conditions: A common type of health statistic that frequently refers to a state of fitness or ill health. Two ways to measure health conditions are the incidence and the prevalence of a disease.
Health Correlates: The risk factors that impact health, including social and economic factors, such as income and education; physical factors like air pollution; and personal behaviors like smoking, exercise, drugs, and alcohol.14
Health Data Interactive: A web-based application from the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS). Health Data Interactive gives access to pre-tabulated national data on a vast array of public health indicators over time.
Health Disparities: "Differences in health outcomes and health care that are closely linked with social, economic, and environmental disadvantage".15
Health Insurance Page, United States Census Bureau: The U.S. Census Bureau website hosts a Health Insurance page with statistical reports, tables, and other data on health insurance coverage and medical services utilization. The U.S. Census Bureau is a bureau of the U.S. Department of Commerce.
Health Statistics: Numbers that summarize information related to health.
Health, United States: A report from the National Center for Health Statistics (NCHS) on national trends in health statistics in the U.S. Health, United States includes detailed tables and charts on selected measures of morbidity, mortality, health status, risk factors, and health care use, among other topics. NCHS is a part of the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS).
Healthcare Cost and Utilization Project (HCUP): A family of databases and related software tools with the largest collection of nationwide and state-specific hospital care data from the Agency for Healthcare Research and Quality (AHRQ), an operating division of the U.S. Department of Health and Human Services (HHS).
Healthdata.gov: A website managed by the Department of Health and Human Services (HHS) that brings together high-value datasets, tools, and applications, offering data about health and health care to help researchers solve problems.16
Hospital Compare: An online tool created by the Centers for Medicare and Medicaid Services (CMS) that helps users find information about the quality of care at over 4,000 Medicare-certified hospitals across the U.S. CMS is an operating division of the U.S. Department of Health and Human Services (HHS).
Hypothesis: A supposed or proposed explanation for the results of a study. Null Hypothesis is the hypothesis that there is no statistically significant difference between two variables. An Alternative Hypothesis is the hypothesis contrary to the null, that there is a statistically significant difference between two variables.
Incidence: The number of new cases of an illness.
Independent Variable(s): A variable that stands alone and isn’t affected by other variables that the study is trying to understand. Independent variables influence dependent variables.
Indirect Standardization: An adjustment procedure used during data analysis designed to remove an extraneous source of variation to allow for comparison between groups with unlike characteristics when the age-specific mortality rates of the population(s) of interest are unknown.17
Kaiser Family Foundation (KFF): A non-profit foundation that runs programs in policy analysis, journalism, and communications. They focus on major health care issues in the U.S. Their goal is to be an unbiased source of facts, information, analysis, and health journalism for the general public, as well as for policy makers, the media, and the health care community.
Medical Expenditure Panel Survey (MEPS): A survey from the Agency for Healthcare Research and Quality (AHRQ), an operating division of the U.S. Department of Health and Human Services (HHS), that gives access to data on the cost and use of health care and health insurance coverage. The information is based on surveys of families and individuals, their medical providers, and employers across the country.18
Medicare and Medicaid Statistical Supplement: Has detailed statistics on Medicare, Medicaid, and other Centers for Medicare and Medicaid Services (CMS) programs. The Supplement has 115 tables and 67 charts that detail health expenditures for the entire U.S. population.19 CMS is an operating division of the U.S. Department of Health and Human Services (HHS).
Morbidity: The disease state (illness) of a population.
National Ambulatory Medical Care Survey (NAMCS): A national survey conducted by the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS), that is designed to meet the need for objective, reliable information about the provision and use of ambulatory medical care services in the U.S. Findings are based on a sample of visits to non-federal employed office-based physicians who are primarily engaged in direct patient care.20
National Center for Health Statistics (NCHS): A Center of the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS), which has a mission to provide statistics and data to guide public policies and actions.21
National Health and Nutrition Examination Survey (NHANES): A program of studies designed to assess the health and nutritional status of adults and children in the U.S. The survey is unique in that it combines interviews and physical examinations and is conducted by the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS).22
National Health Interview Survey (NHIS): A survey from that collects data on a broad range of health topics through personal household interviews. For over 50 years, the U.S. Census Bureau has been the data collection agent for the NHIS.23 The U.S. Census Bureau is a bureau of the U.S. Department of Commerce.
National Healthcare Quality and Disparities Reports: Yearly publications of the Agency for Healthcare Research and Quality (AHRQ), an operating division of the U.S. Department of Health and Human Services (HHS), that track trends in care effectiveness, patient centeredness, timeliness of care, patient safety, efficiency of care, and health equity.
National Survey of Children’s Health (NSCH): A survey sponsored by the Health Resources and Services Administration (HRSA), an operating division of the U.S. Department of Health and Human Services (HHS) that touches on multiple, intersecting aspects of children’s lives. The survey includes physical and mental health status, access to quality health care, as well as information on the child’s family, neighborhood and social context.24
National Vital Statistics System: Provides access to the official vital statistics of the U.S., including births, deaths, marriages, and divorces. The webpage features links to statistical reports, an interactive data query tool, and downloadable data files. The National Vital Statistics System is a resource of the National Center for Health Statistics (NCHS) at the Centers for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS).
Natural Experiment: A situation under investigation which occurs due to factors unrelated to the researchers.
Nonprobability Sampling: A type of sampling that does not involve random selection and so cannot rely on probability theory to ensure that it is representative of the population of interest.
Pearson’s Correlation Coefficient: A commonly-used measure of linear causation which shows the extent to which two variables relate to one another, denoted by the symbol ρ for population, or the letter r for a sample. Its value always lies between -1 and 1.
Population: In research, the population is the entire set of individuals that are of interest to the researcher.
Precision (or Reliability): A measure of how often researchers would get the same answer if they conducted the same study over and over.
Prevalence: The total number of people with a certain illness at a specific time.
Probability Sampling: Probability sampling involves random selection, and is common because each person in the group or community has an equal chance of being chosen. In statistical theory based on probability, this means that the sample is more likely to resemble the larger population, and thus more accurate inferences can be made about the larger population.
Public Health Surveillance: A type of record collection that helps us study infectious diseases. The Centers for Disease Control and Prevention (CDC), World Health Organization (WHO), and other institutions collect, analyze, and interpret data that they collect from local and state health departments. They use this information to prevent and control the spread of disease.
Quality: How well a health plan keeps its members healthy or treats them when they are sick. Good quality health care means doing the right thing at the right time, in the right way, for the right person and getting the best possible results.25
Quality of Life: "a broad multidimensional concept that usually includes subjective evaluations of both positive and negative aspects of life". Health Related Quality of Life (HRQOL) is an individual’s or group’s perceived physical and mental health over time.26
Random Sampling: A random sample is a sample whose members are chosen at random from a given population in such a way that the chance of obtaining any particular sample can be computed.27
Randomized Control Trial (RCT): "A study design that randomly assigns participants into an experimental group or a control group. As the study is conducted, the only expected difference between the control and experimental groups in a randomized controlled trial (RCT) is the outcome variable being studied".28
Reliability (or Precision): A measure of how often researchers would get the same answer, if they did the same study over and over.
Risk Adjustment: An actuarial tool used to calibrate payments to health plans or other stakeholders based on the relative health of the at-risk populations.29
Robert Wood Johnson Foundation (RWJF): The largest philanthropy organization in the U.S. dedicated solely to health.30 RWJF funds a variety of grants that improve the health and health care of all Americans.
Robert Wood Johnson Foundation County Health Rankings & Roadmaps: An interactive online application from the Robert Wood Johnson Foundation. It ranks the overall health status of almost every U.S. County. It offers access to measures of health outcomes like mortality and morbidity, and their determinants, such as health behaviors, clinical care, social and economic factors, and physical environment.
Sample: A subset of the population that is actually used in research. One common method for selecting a sample is called probability sampling. In probability sampling, each person in the group or community has an equal chance (probability) of being chosen.
Sampling Error: The approximate difference between the results from a sample of people from a larger group, and the likely results of studying every single person in that group. In general, the larger the sample size is, the smaller the sampling error.
Sampling Frame: The set of information about the accessible units in a sample.
State Health Facts: From the Kaiser Family Foundation, State Health Facts has more than 800 health indicators for all 50 states, Washington, D.C., U.S. Territories, and other locations. Users can view maps, relative health rankings, trends, and download data on demographics, health costs, health coverage, minority health, providers and service use, and more.
Statistical Significance: The significance level of a hypothesis test is the chance that the test erroneously rejects the null hypothesis (the hypothesis we wish to falsify on the basis of the data) when the null hypothesis is true.31
Statistical Validity (or Accuracy): Refers to the soundness of research design and methods, and whether researchers are actually measuring what they intend to study.
Temporal Precedence: Part of the process of establishing causation. An independent variable cannot have a causal relationship with the dependent variable unless the hypothesized cause happens before the measured effect.
United States Census Bureau: The best source for current data and statistics about the population and economy of the U.S. The Census Bureau collects and gives out information about health insurance coverage for adults and children. The Census Bureau is a bureau of the U.S. Department of Commerce.
Validity: The accuracy of the measurement provided by a specific tool. Internal validity is the extent to which the observed effects of a variable can be attributable to the hypothesized cause. External validity is the extent to which results of experiment can be generalizable to larger populations.
Vital Records: Include births, deaths, marriages, divorces, and fetal deaths. They also record information about the cause of death, or details of the birth. Vital Records are collected by the National Vital Statistics System within the National Center for Health Statistics (NCHS), Center for Disease Control and Prevention (CDC), an operating division of the U.S. Department of Health and Human Services (HHS). Vital records data are provided through contracts between NCHS and vital registration systems operated in the various jurisdictions legally responsible for the registration of vital events.
World Health Organization (WHO): An agency within the United Nations (UN) that provides leadership on global health issues. WHO collects, compiles, and disseminates a wide range of data used to monitor and assess health trends worldwide.
World Health Statistics Report: A yearly publication of the World Health Organization (WHO) of the United Nations (UN) which presents the most recent health statistics of its 194 Member States.
Youth Risk Behavior Surveillance System (YRBSS): From the Centers for Disease Control and Prevention (CDC) which monitors six types of health-risk behaviors that contribute to the leading causes of death and disability among youth and adults. The CDC is an operating division of the U.S. Department of Health and Human Services (HHS).32
z-score: The number of standard deviations above or below the mean value.
1. "Read the Affordable Care Act." HealthCare.Gov, A federal government website managed by the U.S. Centers for Medicare & Medicaid Services, n.d. www.healthcare.gov/where-can-i-read-the-affordable-care-act/.
2. "Age-Adjusted Rate Definitions." Missouri Department of Health & Senior Services, https://health.mo.gov/data/mica/CDP_MICA/Age-specificRate.html.
3. "Behavioral Risk Factor Surveillance System (BRFSS)." Centers for Disease Control and Prevention, 5 May 2023, www.cdc.gov/brfss/.
4. "Bias, Confounding and Effect Modification" Stat 507, Epidemiological Research Methods, Penn State Eberly College of Science, 2017 Web 1/24/17.
5. "Causation." University of California Berkeley Glossary of Statistical Terms, www.stat.berkeley.edu/~stark/SticiGui/Text/gloss.htm.
6. "Chronic Conditions PUF." CMS.Gov, https://www.cms.gov/Research-Statistics-Data-and-Systems/Downloadable-Public-Use-Files/BSAPUFS/Chronic_Conditions_PUF.
7. "Glossary: Claim." CMS.Gov, https://www.cms.gov/glossary?term=claim.
8. "Correlation." University of California Berkeley Glossary of Statistical Terms, www.stat.berkeley.edu/~stark/SticiGui/Text/gloss.htm.
9. "Degrees of Freedom." The University of Texas at Austin Statistics Online Support, 2015, https://sites.utexas.edu/sos/degreesfreedom/.
10. Meinert, C. (1996). Clinical Trials Dictionary: Terminology and Usage Recommendations. Center for Clinical Trials, publisher, Baltimore, as cited in Diener-West, M., and S. Kanchanaraksa (2008). The Direct and Indirect Methods of Adjustment (Presentation). Johns Hopkins Bloomburg School of Public Health.
11. Naing, N. N. (2000). Easy Way to Learn Standardization: Direct and Indirect Methods. The Malaysian Journal of Medical Sciences. Jan; 7(1): 10–15.
12. Masic, I., Miokovic, M. and B. Muhamadagic. Evidence Based Medicine- New Approaches and Challenges. Acta Informatica Medica, 16(4). 2008.
13. Oxman, A.D., Laivs, J.N., Lewin, S., and A. Fretheim. SUPPORT Tools for evidence-informed health Policymaking (STP)1: What is evidence-informed policymaking? Health Research Policy and Systems, 7(S1). 2009.
14. "Health Impact Assessment." World Health Organization, https://www.nlm.nih.gov/nichsr/stats_tutorial/glossary.html#_ftn1.
15. U.S. Dept. of Health and Human Services, Office of the Secretary, Office of the Assistant Secretary for Planning and Evaluation and Office of Minority Health. HHS Action Plan to Reduce Racial and Ethnic Health Disparities Implementation Progress Report. Washington, DC: Office of the Assistant Secretary for Planning and Evaluation, 2015.https://aspe.hhs.gov/reports/hhs-action-plan-reduce-racial-ethnic-health-disparities-implementation-progress-report-2011-2014-0.
16. "Healthdata.Gov." U.S. Department of Health and Human Services, https://healthdata.gov/.
17. Naing, N. N. (2000). Easy Way to Learn Standardization: Direct and Indirect Methods. The Malaysian Journal of Medical Sciences. Jan; 7(1): 10–15. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3406211/.
18. "Medical Expenditure Panel Survey (MEPS)." Agency for Healthcare Research and Quality, https://meps.ahrq.gov/mepsweb/.
19. "Medicare & Medicaid Statistical Supplement." CMS.Gov, https://www.cms.gov/research-statistics-data-and-systems/statistics-trends-and-reports/archives/mmss.
20. "Ambulatory Health Care Data." Centers for Disease Control and Prevention, www.cdc.gov/nchs/ahcd/index.htm?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fnchs%2Fahcd.htm.
21. "The NCHS Mission." Centers for Disease Control and Prevention, https://www.cdc.gov/nchs/about/mission.htm.
22. "National Health and Nutrition Examination Survey (NHANES)." Centers for Disease Control and Prevention, https://www.cdc.gov/nchs/nhanes/index.htm?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fnchs%2Fnhanes.htm.
23. "National Health Interview Survey (NHIS)." Centers for Disease Control and Prevention, https://www.cdc.gov/nchs/nhis/index.htm?CDC_AA_refVal=https%3A%2F%2Fwww.cdc.gov%2Fnchs%2Fnhis.htm.
24. "The National Survey of Children’s Health." Data Resource Center for Child and Adolescent Health, https://www.childhealthdata.org/learn-about-the-nsch/NSCH.
25. "Glossary: Quality." CMS.Gov, https://www.cms.gov/glossary?term=quality.
26. Centers for Disease Control and Prevention. Measuring Healthy Days. Atlanta, Georgia: CDC, November 2000. https://www.cdc.gov/hrqol/pdfs/mhd.pdf.
27. "Random Sample." University of California Berkeley Glossary of Statistical Terms, www.stat.berkeley.edu/~stark/SticiGui/Text/gloss.htm.
28. "Randomized Controlled Trial." Himmelfarb Health Sciences Library, 2019, https://himmelfarb.gwu.edu/tutorials/studydesign101/rcts.cfm.
29. "Risk Assessment and Risk Adjustment." American Academy of Actuaries: Issue Brief, May 2010, https://www.actuary.org/sites/default/files/pdf/health/Risk_Adjustment_Issue_Brief_Final_5-26-10.pdf.
30. "About the Robert Wood Johnson Foundation." Robert Wood Johnson Foundation, https://www.rwjf.org/en/about-rwjf.html.
31. "Significance, Significance level, Statistical significance." University of California Berkeley Glossary of Statistical Terms, www.stat.berkeley.edu/~stark/SticiGui/Text/gloss.htm.
32. "Youth Risk Behavior Surveillance System (YRBSS)." Centers for Disease Control and Prevention, https://www.cdc.gov/healthyyouth/data/yrbs/.