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What is Epidemiology? It is the study of the distribution and determinants of health, disease, and injury in human populations. A key question in epidemiology is why some people are healthy/sick while others are not.

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Two Basic Assumptions of Epidemiology:

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Human disease does not occur randomly.

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Human disease has causal and preventive factors that can be identified through systematic investigation.

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Origin and Definition: The term epidemiology comes from Greek, meaning "the study of what is upon the people". It describes the frequency and patterns of morbidity and mortality in terms of person, place, or time.

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Scope of Epidemiology: Epidemiology can potentially study the occurrence of anything related to health.

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Goal of Epidemiology: The goal is to describe or explain the occurrence of health, disease, injury, or health-related conditions in a community or group of people.

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Applications of Epidemiology:

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Identifying risk factors for disease, which helps in understanding disease causation.

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Evaluating treatment efficacy, such as through randomized controlled trials.

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Investigating disease outbreaks.

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Other uses include public health planning and prioritizing, needs assessments, setting objectives, program evaluation, formulating health policy, understanding the natural history of disease, estimating individual risk, and completing the clinical picture of a disease. Physicians may have an incomplete understanding of a disease's severity and distribution because they only see those who seek treatment.

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Outbreak: An outbreak, also known as an epidemic, is a clear increase in the number of "cases" of a disease or health-related condition above normal baseline levels.

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The Pyramid/Iceberg of Disease: This model illustrates different states of disease within a population, ranging from diagnosed and controlled cases to those with risk factors but no disease. The levels are: 1. Diseased, diagnosed & controlled, 2. Diagnosed, uncontrolled, 3. Undiagnosed or wrongly diagnosed disease, 4. Risk factors for disease, 5. Free of risk factors.

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Three Types of Epidemiology:

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Descriptive Epidemiology: Describes the frequency and patterns (distribution) of morbidity and mortality by person, place, and time (Who-Where-When). Examples include populations where a disease does/does not occur, common geographic locations, and frequency over time.

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Analytic Epidemiology: Focuses on the determinants of disease, asking Why/How (causes). It involves testing hypotheses formulated from descriptive studies and identifying factors associated with health conditions, aiming to predict and potentially prevent them.

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Clinical Epidemiology: Patient-oriented and seeks to aid decision-making about diagnosis, prognosis, and treatment of disease. Its goal is to prevent, reduce, or control morbidity and mortality in human populations.

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Evolution of Epidemiology: It started as an attempt to explain disease systematically.

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Pandemic Example: The Plague (Black Death) from 1347-1351 killed over 30% of Western Europe's population (25 million) and 60 million people worldwide.

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Early Pioneers:

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Hippocrates (460-377 B.C.): One of the first to base conclusions on observations, offering rational explanations and considering individuals and populations, as well as the association of environmental and other factors like air, water, places, and personal habits (drinking, diet, exercise).

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John Graunt (1620-1674): Known as the "Father of Biostatistics" for publishing weekly and annual records of births and deaths ("Bills of Mortality"), quantifying disease patterns, associating births and deaths with factors like age and sex, observing seasonal fluctuations in deaths and patterns in infant mortality, and developing quantitative methods.

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Dr. John Snow (1813-1858): Widely considered the father of modern epidemiology for his work on cholera transmission. He demonstrated the transmission of cholera through contaminated water by observing higher cholera deaths in districts served by water companies drawing from sewage-contaminated parts of the Thames River. His investigation of the Broad Street pump outbreak in 1854, mapping cases and linking them to the pump, further confirmed cholera as a water-borne disease; removing the pump handle ended the outbreak.

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James Lind (1716-1794): A naval surgeon who conducted an early controlled trial by dividing scurvy-stricken soldiers into groups with different dietary supplements, finding that citrus fruit improved their condition.

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Edward Jenner (1749-1823): An English surgeon who performed the first smallpox immunizations using cowpox vaccine after observing milkmaids' immunity, paving the way for preventive medicine.

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Austin Bradford-Hill (1897-1991): His 1950s studies proved a causal link between smoking and lung cancer, accelerating the growth of epidemiology. He developed the "Bradford-Hill Criteria" (1965), a checklist to assess the causality of an association, including strength, plausibility, consistency, coherence, specificity, experimental evidence, temporality, analogy, and biological gradient.

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Key 20th Century Developments:

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Framingham Heart Study (1948): Initiated due to the rise of cardiovascular disease (CVD) in the US, it aimed to understand why CVD became the leading cause of death and coined the term "risk factors".

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U.S. National Health Examination Survey (1959): A large-scale survey that has continued to collect data from 140,000 people.

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Canadian Health Measures Survey (2007).

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Epidemiology @ the UofR: Research at the University of Regina focuses on exploring physical activity (PA) and sedentary behaviour (SB) in healthy and clinical populations across the lifespan. This includes studying PA & SB trends, correlates, determinants, and their associations with various health outcomes using pre-existing databases and collected data