Epidemiology, Broadly Speaking
Epi Explained
Plain-language explanations that start with the question, name the parts of a calculation, and show how to use a concept without overstating what it can prove.
Core concept
Public health brings evidence and community action together to prevent harm and improve health across populations. Here is how that work connects with individual care.
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Explore herd immunity and threshold calculations, with examples and limitations that affect how population protection is interpreted.
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Learn why age adjustment is used, how direct standardization works, and how to interpret comparisons between populations with different age structures.
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Explore how health indicators describe population health, guide comparisons and inform decisions, including limits of the underlying data.
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Learn how risk factors are identified and interpreted, with examples showing why association, context and study limitations matter.
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Learn what epidemic curves show, read their axes and patterns, and examine how reporting and missing data affect outbreak interpretation.
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Explore non-pharmaceutical interventions, from personal measures to community and environmental actions, with implementation tradeoffs and limits.
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Follow the work of an outbreak investigation, from identifying cases and testing hypotheses to control measures, communication and monitoring.
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Learn how descriptive epidemiology organizes health data by person, place and time, with examples, data sources and interpretive limits.
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Explore time-to-event analysis, survival curves, censoring and model interpretation, with applications and limitations in health research.
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Outbreak types describe how a disease reaches people: a shared brief exposure, an ongoing source, sporadic contact, or person-to-person spread. Each pattern produces a different epidemic curve shape. Learn to read that shape, connect it to an investigation hypothesis, and understand why the curve generates evidence rather than proof.
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Understand morbidity and mortality, compare measures of illness and death, and see how public health uses them to describe population health.
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Explore p-values, z-scores and hypothesis testing, including how statistical significance is interpreted and where it can mislead.
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Learn how prevalence describes existing cases, compare point and period prevalence, and examine how prevalence differs from incidence.
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Learn how incidence rates count new cases over person-time, work through a calculation, and distinguish incidence rate from cumulative incidence.
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Learn how sensitivity and specificity describe test results, calculate them, and distinguish them from positive and negative predictive values.
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Explore selection bias, information bias, confounding and random error, with examples of how study methods affect interpretation.
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Compare epidemic, pandemic and endemic patterns, with examples showing how public health describes disease occurrence and geographic spread.
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Explore random assignment, comparison groups and the structure of randomized controlled trials, including practical and interpretive limitations.
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Learn how case-control studies select cases and controls, compare prior exposures, and use odds ratios to describe associations.
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