PUBHLTH EXAM 2

What is epidemiology

1: the study of health and disease in populations.

2.: the study of the distribution and determinants of disease frequency in human populations.

5 main objectives of field of epidemiology

1. Identify the cause of disease and its risk factors

2. Determine the extent of disease found in the community

3. Study the natural history and prognosis of disease

4. Evaluate new preventative and therapeutic measures

5. Provide a foundation for developing public policy

Epidemiology’s role in public health

Epidemiology’s role in public health is to develop and apply methods for assessing health and disease

7 tools in epidemiology toolkit

1. asking questions

2. measurement

3. study design

4. statistical analysis

5. prevention

6. surveillance

7. outbreak investigations

explain elements of asking questions (tool #1)

Exposure (independent) --> outcome (dependent)

(clearly defined Study sample and specified time period)

explain what measurement includes (tool #2)

Measurement of a population

• Define who counts, population boundaries, and relevant demographic categories.

Measurement of exposure

• What defines exposure? Can you delineate between exposed/unexposed? Are there categories/levels to exposed?

Measurement of an outcome

• Measure disease occurrence, mortality, hospitalizations, or other health outcomes.

Identify the 4 Main Epidemiological Studies

1. Randomized control trials

2. Cohort studies

3. Case-control studies

4. Cross-sectional studies

Explain randomized control trials

Participants randomly assigned to intervention or control groups.

Compares health outcomes from both groups to evaluate effect

Explain prospective cohort studies

Begin with exposed and unexposed disease-free groups and follow them over time.

Explain Case-Control Studies

Begin with diseased cases and nondiseased controls, then look backward at exposure histories.

Explain Cross-sectional studies

Measures exposure and health outcomes at the same point in time to identify associations. *Cannot establish temporality (which came first), so it cannot determine causation.

What are some commonly used statistical measures?

Odds ratio

Incidence/Prevalence of disease

Explain how to determine odds ratio

Odds Ratio = (Diseased exposed / Diseased unexposed) ÷ (Nondiseased exposed / Nondiseased unexposed)

Explain prevention (tool #5)

Prevention is where epidemiologic methods translate into public health practice

How many levels of prevention are there and what are their names?

3: Primary prevention, secondary prevention & tertiary prevention

explain primary prevention & provide 3 examples

Stops disease before it starts

Ex. Vaccines, seat belts, water fluoridation

explain secondary prevention & provide an example

catch early disease or risk factors

Ex. Cancer screening, blood pressure checks

explain tertiary prevention & provide an example

Manage disease and prevent complications

Ex. Cardiac rehabilitation

How does the CDC defines surveillance? (tool #6)

“Public health surveillance is the ongoing, systematic collection, analysis, and

interpretation of health-related data essential to planning, implementation,

and evaluation of public health practice.”

Define endemic vs epidemic vs pandemic

Endemic: the usual occurrence of a disease within a given geographic area and time period

Epidemic: the occurrence of an infectious disease clearly in excess of normal expectancy

Pandemic: a worldwide epidemic affecting an exceptionally high proportion of the global population

How do you know if there is an outbreak (tool #7)

Look at the number of cases endemically

Is there an uptick from the endemic numbers?

• Could be coming from surveillance reports, mortality records, hospital records, etc.

What 10 things happen when an outbreak investigation is triggered?

1. Prepare for field work

2. Establish existence of an outbreak

3. Verify the diagnosis

4. Define and identify cases

5. Describe the data in terms of person, place, and time

6. Develop hypotheses

7. Evaluate hypotheses

8. Carry out additional studies

9. Implement control and prevention measures

10. Communicate findings

What is biostatistics?

The application of mathematical logic and statistical reasoning to medical and health-related data.

List 3 ways in which biostatisticians contribute to evidence-based public health

• Study design: Select optimal study designs and determine sample sizes using statistical power.

• Bias: Identify sources of bias and use statistical methods to correct or account for them.

• Measurement accuracy: Evaluate measurement errors and adjust estimates when possible.

• Missing data: Determine whether missing data is ignorable or non-ignorable and use imputation when appropriate.

• Statistical associations: Analyze relationships between exposures and health outcomes.

• Sampling variability: Quantify uncertainty in estimates using statistical methods.

• Confounding: Identify potential confounders and use study designs or statistical methods to reduce their effects.

• Interpretation: Distinguish statistical significance from practical significance and combine evidence across studies.

Define statistical bias and possible sources

Definition: Statistical Bias is the systematic error in the estimation of a quantity of interest that causes the expected value of a statistic to differ from the true population value.

Statistical bias occurs when your data gives you the wrong answer because something in the way you collected or analyzed it was off.

Sources:

• Sample selection bias — Selecting a sample that is not representative of the intended population.

• Measurement error — Systematically overestimated or underestimated measurements

• Missing data — Missing information that can distort results

• Confounding — Hidden variables that distort exposure–outcome relationships

Define Statistical Association

As the exposure changes, the outcome tends to change with it

Strength of evidence depends on:

• Study design

• Magnitude of the effect

• Accuracy of measurements

• Accounting for uncertainty and confounding

Define Statistical Significance

An observed result is more extreme than what would be expected simply by chance, assuming no true effect.

• Indicates evidence of a non-zero effect, not necessarily a large effect

What does Statistical Association Not Mean?

Statistical association indicates that variables are related, but does not prove causation or practical importance.

• Correlation ≠ Causation: A strong statistical association does not prove that one variable causes another.

• Statistical significance ≠ Practical significance: A statistically significant result may not have meaningful real-world effects.

  • Ex. A statistically significant GPA increase of only 0.02 points.

• Confounding: A hidden variable may distort the relationship between exposure and outcome.

Define/Explain Sampling Variability

Estimates from a sample are not perfect and will differ from sample to sample due to chance.

• Biostatisticians use statistical methods to quantify uncertainty in estimates.

Name Ways to Account for Sampling Variability

• Confidence Intervals: Provide a range of plausible values for a population quantity.

• Margin of Error/Error Bars: Represent uncertainty around an estimate.

• P-values: Probability of observing results as extreme or more extreme than those obtained, assuming no actual effect.

• Sample Size: Larger samples generally produce more precise estimates.

• Statistical Power: Probability of detecting a statistically significant effect when a true effect exists; used to determine appropriate sample sizes.

Define Confounding

Confounding is the effect of a “hidden” variable(s) that distorts the relationship between exposure and outcome. 

Ex:

• Ice cream sales ↔ Shark attacks: Summer (season) is the confounder.

• Shoe size ↔ Reading ability: Age is the confounder.

• Coffee consumption ↔ Cancer risk: Smoking is the confounder.

• Acetaminophen use during pregnancy ↔ Childhood asthma: Maternal infections and fever are potential confounders.

Why does identifying confounding matter?

• Failing to account for confounding can lead to biased results and incorrect interpretations.

• An observed association may be explained by a third variable rather than a causal relationship.

Ways to account for confounding?

• Randomized trials: Gold standard for reducing confounding through random assignment.

• Statistical methods: Used to reduce the impact of confounding in observational studies.

• Biostatisticians suggest study designs and methods to minimize confounding.

Define infectious disease

• “disorders caused by organisms — such as bacteria, viruses, fungi or parasites. Many organisms live in and on our bodies. They're normally harmless or even helpful, but under certain conditions, some organisms may cause disease.”

• “Some infectious diseases can be passed from person to person. Some are transmitted by bites from insects or animals. And others are acquired by ingesting contaminated food or water or being exposed to organisms in the environment”.

1. Describe how the understanding of infectious diseases changed from the beginning to the end of the 19th century (1800s)

• Early 1800s — Miasma Theory: Disease was believed to be caused by bad air.

  • Sanitarians, including Florence Nightingale, promoted removing garbage and creating open-air treatment spaces.

  • Wrong cause, but often effective remedies.

• 1840 — Jacob Henle: Embraced the then-unpopular theory that microorganisms cause infectious diseases.

• 1840s — Ignaz Semmelweis: Implemented chlorine handwashing, dramatically reducing deaths from childbed fever.

• 1854 — John Snow: Used maps to trace a cholera outbreak to sewage-contaminated water from the Broad Street pump, challenging miasma theory.

• 1860s — Louis Pasteur: Provided biological evidence for germ theory by showing that microorganisms/particles in air, rather than air itself, caused spoilage.

  • Developed pasteurization and vaccines against anthrax and rabies.

• Late 1800s — Robert Koch: Further developed germ theory and established four criteria (Koch's postulates) for linking microorganisms to diseases.

  • Identified bacteria responsible for tuberculosis and cholera.

• Overall shift: Miasma theory (bad air) → Germ theory (microorganisms cause disease).

Name factors that have led to the reemergence of infectious diseases

• Spread of antimicrobial resistance.

• Increasing human contact with the environment, especially animals.

  • Examples: HIV-1 (primates), influenza (birds/pigs), Lyme disease (ticks), plague (rodents).

• Urbanization and crowding.

• Increasing mobility.

• Potential for bioterrorism.

• Increasing pollutants.

• Aging population.

• Effects of global warming.

Explain ways infectious diseases are transmitted

• Direct contact: Pathogen passes person-to-person without a contaminated intermediate object.

  • Examples: Touching, sneezing, sexual intercourse.

• Indirect contact: Pathogen passes through a contaminated inanimate object.

  • Examples: Toys, food, water.

• Vector-borne: Pathogen transmitted through an infected/contaminated vector.

  • Examples: Mosquitoes, ticks, mice.

4 possible outcomes of transmission

• No infection: Exposure does not result in infection.

• Subclinical infection: Infection occurs without noticeable clinical illness.

• Clinical infection: Infection produces recognizable symptoms.

• Carrier, no illness: Individual carries the pathogen without becoming ill.

3 phases of infectious process

• Incubation period: Time between infection and onset of symptoms.

• Latent period: Time between infection and becoming infectious (able to transmit the pathogen).

• Infectious period: Period when an infected individual can transmit the pathogen to others.

  • *Important: The infectious period can begin before symptoms appear, meaning someone may transmit disease during the incubation period.

Wikipedia definition of chronic disease

“a health condition that is persistent or otherwise longlasting in its effects or a disease that comes with time”

CDC definition of chronic disease

“chronic diseases are defined broadly as conditions that last 1 year or more and require ongoing medical attention or limit activities of daily living or both”

World Health Organization Definition of Noncommunicable disease

“Diseases not spread through infection or other people, lasting a long time and resulting from genetic, physiological, environmental, and behavioral factors.”

Identify the Similarities & Differences between the 3 definitions of chronic disease

Similarities: All emphasize long-lasting conditions.

Differences:

• Wikipedia: Broadest definition; focuses on persistence.

• CDC: Specifies duration (1+ years) and medical attention/activity limitations.

• WHO: Emphasizes noncommunicability and multiple contributing factors.

List CDC’s Major Chronic Diseases

Heart disease, cancer, chronic lung disease, stroke, Alzheimer's disease, diabetes, and chronic kidney disease.

What conditions challenge the CDC’s Definition of Chronic Disease

• Stroke: An acute event that can cause long-term consequences.

• HIV: Infectious/communicable but can become a lifelong condition requiring treatment.

• Arthritis, asthma, lupus, depression, obesity: Conditions discussed as potentially chronic despite not appearing on the slide's main CDC list.

What is the Prevalence of Chronic Disease In the US

Nearly 60% of U.S. adults have a chronic disease; 4 in 10 of those have 2+ chronic conditions

What is the Health burden of chronic diseases

Leading causes of disability, reduced quality of life, and mortality.

• DALYs: Measure disease burden by accounting for years lost to premature death and disability.

Describe the economic burden of chronic disease

• 90% of $4.1 trillion in annual U.S. healthcare expenditures are for chronic and mental health conditions.

• Heart disease costs $215 billion annually plus $147 billion in lost productivity.

• Chronic diseases can contribute to other chronic diseases, increasing the burden.

Describe the individual burden of chronic diseae

Survival, quality of life, social consequences, financial costs, worry/anxiety.

Describe the population burden of chronic disease

Prevalence, incidence, morbidity, mortality, healthcare costs, and economic impact.

Categorize the 4 burdens of chronic disease

• health burden

• economic burden

• individual burden

• population burden

Describe the epidemiologic transition

Shift from infectious diseases being major causes of death to chronic diseases becoming dominant.

• In the U.S., infectious diseases such as tuberculosis and pneumonia dominated in 1900; heart disease and cancer became leading causes later.

List the modifiable factors of chronic disease

• Tobacco use / secondhand smoke.

• Poor nutrition.

• Physical inactivity.

• Excessive alcohol use.

• Poor sleep.

• Missing: Environmental exposures (air pollution, water quality)

List the non-modifiable factors of chronic disease

• Age.

• Genetics.

• Family history.

Describe racial/ethnic trends of heart disease in US

Despite the prevalence of heart disease being highest in non-hispanic white adults, the death rates are highest in non-hispanic black adults

• Heart disease prevalence by race/ethnicity (2017):

  • Non-Hispanic White adults: 11.5%.

  • Non-Hispanic Black adults: 9.5%.

  • Hispanic adults: 7.4%.

  • Non-Hispanic Asian adults: 6.0%.

• Heart disease death rates:

  • Non-Hispanic Black adults have the highest heart disease mortality despite non-Hispanic White adults having the highest prevalence in the slide's data.

  • Death rates declined for all displayed racial/ethnic groups from 1999–2017.

  • Non-Hispanic Asian/Pacific Islander adults had the lowest death rates in the graph.

Describe geographic trends of heart disease rates in US

Highest heart disease mortality shifted from the Northeast/Midwest toward the South/Southeast

Explain the role of public health in primary prevention of chronic diseases

Prevent disease before it occurs

• Health education and promotion: Encourage healthy behaviors and avoidance of risk factors.

• Policy interventions: Reduce population exposure to health risks.

• Community-based interventions: Support disease prevention at the community level.

• Examples:

  • Tobacco control policies to reduce smoking and lung cancer deaths.

  • Million Hearts initiative to prevent heart attacks and strokes.

Explain the role of public health in secondary prevention of chronic diseases

Detect disease or risk factors early

• Screening: Identify disease early to prevent serious health outcomes.

• Examples: Bone density screening, blood pressure checks, and cancer screenings.

• Includes early identification, treatment, and updated screening guidelines.

Describe person first language in healthcare & provide examples

• Person-first language: Language that emphasizes the person as a whole and views their disease, condition, or disability as only one part of them.

• Avoids labeling individuals by their conditions, which can create stigma and bias.

• Examples:

  • "Obese person" → "Person with obesity"

  • "Diabetic" → "Person with type 2 diabetes"

  • "Addict" → "Person with addiction"

• Exception: Some disabled or neurodivergent individuals prefer identity-first language because their condition is an important part of their identity.

Trends in chronic disease in US

• Obesity is a chronic condition involving excess adipose tissue that may affect health.

  • Obesity prevalence has increased since the 1960s, with a sharp increase beginning around 1980.

  • Obesity is highly prevalent, has serious health/economic consequences, and is preventable and treatable.

• Other chronic diseases associated with diet and physical inactivity include type 2 diabetes, heart disease, hypertension, and stroke.

How do trends for chronic disease in the U.S. relate to changes in diet and physical activity?

• Dietary changes: Rise of fast-food chains and high-fructose corn syrup (discussed in lecture).

• Physical activity changes: Increased sedentary lifestyles, desk jobs, and electronics use.

• Other contributing factors: Genetics, sleep, and environmental exposures.

• Poor nutrition and physical inactivity contribute to obesity, type 2 diabetes, heart disease, and other chronic diseases.

• Nutritional risk factors include excess added sugar, sodium, saturated/trans fats, and insufficient fruits, vegetables, and fiber.

What did the Diabetes Prevention Program (DPP) demonstrate?

• Randomized trial of approximately 3,200 adults with prediabetes and overweight/obesity.

• Compared placebo, metformin, and intensive lifestyle intervention (diet and physical activity).

• Intensive lifestyle intervention produced the lowest incidence of type 2 diabetes, followed by metformin, then placebo.

• Demonstrated that dietary and physical activity changes can help prevent chronic disease.

What are the classes of nutrients?

• Macronutrients: Carbohydrates, lipids/fats, proteins — provide energy (calories).

• Micronutrients: Vitamins and minerals — needed in smaller amounts for bodily functions.

• Water: Essential for bodily function.

What are Dietary Reference Intakes (DRIs)?

• Daily energy and nutrient intake recommendations based on age, sex, and life stage (e.g., pregnancy/lactation).

• Purpose: Prevent deficiencies and excesses, reduce chronic disease risk, and maintain health.

• RDA: Recommended Dietary Allowance.

• UL: Tolerable Upper Intake Level (maximum intake unlikely to cause harm).

• Example: Folic acid fortification of cereal grains and wheat flour became mandatory in 1998 to reduce neural tube defects.

Front: What are the Dietary Guidelines for Americans (DGAs)?

• Developed through expert review every 5 years under HHS and USDA.

• Goals: Promote health, prevent chronic disease, and provide tools to monitor food intake.

• Nutritional risk factors for chronic disease discussed in the slides:

  • Excess added sugar, sodium, saturated/trans fats, and alcohol.

  • Low intake of fruits, vegetables, fiber, vitamins, and minerals.

• ex food pyramid, my plate etc

What are the age groups for physical activity reccomendations?

children 3-5

adolescents 6-17

adults age 18+

What are the physical activity reccomendations for children age 3-5

• Caretakers should encourage active play.

What are the physical activity reccomendations for adolecents age 6-17

At least 60 minutes/day of moderate-to-vigorous physical activity.

What are the physical activity reccomendations for adults age 18+

Adults ages 18+:

• 150–300 minutes/week of moderate-intensity aerobic activity OR 75–150 minutes/week of vigorous activity.

• Muscle-strengthening activities at least 2 days/week, targeting all major muscle groups.

What are the benefits to meeting physical activity reccomendations?

Prevents chronic disease, improves sleep, cognitive function, mental health, daily physical function, and maintains muscle/bone mass.

Why are there are complex relationships between diet, exercise and weight status?

• Obesity and chronic disease risk are influenced by multiple factors, not just individual diet and exercise choices.

• Social determinants of health influence access to healthy food, safe places for physical activity, and opportunities to maintain healthy behaviors.

• Lecture examples:

  • Higher rates of obesity and type 2 diabetes among lower socioeconomic status populations, Black and Hispanic populations, and individuals with lower educational attainment.

  • Lower diet quality and greater nutrient deficiencies among lower socioeconomic status and education groups.

  • Neighborhood differences in sidewalks, safe walking spaces, grocery stores, and convenience stores.

What complex factors influence weight status other than diet and exercise

Social determinants of health:

• Socioeconomic status

• Education level

• Race/ethnicity

• Environmental conditions

• Access to healthy food

• Access to safe places for physical activity

What is a vaccine and what form of prevention is it

• A substance that prepares the body to fight disease by stimulating an immune response.

  • Vaccines stimulate the production of protective immune cells and antibodies, creating immunity.

  • Purposes:

    • Prevent disease or infection.

    • Reduce the risk of severe symptoms and complications.

    • Provide immunity before exposure to disease.

  • Vaccines are preventive, NOT cures for existing infections.

• Primary prevention: Preventing disease before it occurs.

what are the Stages of Vaccine Development

1. Exploration

2. Preclinical testing

3. Clinical testing (Phases 1–3)

4. Regulatory review and approval (FDA)

5. Production and quality control

What are the Vaccine Development Clinical Phases

• Phase 1 (20–100 volunteers): Evaluates safety, dosage, initial immune response, and serious side effects.

• Phase 2 (Several hundred volunteers): Evaluates common short-term side effects and immune responses.

• Phase 3 (Hundreds to thousands of volunteers): Compares vaccinated and unvaccinated groups to evaluate safety, effectiveness, and side effects.

What is herd immunity?

When enough people in a population are immune to a disease, its spread is limited, indirectly protecting people who are not immune.

What are the benefits of herd immunity?

• Reduces transmission of infectious diseases.

• Protects individuals who cannot receive certain vaccines due to age, allergies, or medical conditions.

• Prevents outbreaks and protects vulnerable populations.

Does everyone need to be vaccinated for herd immunity?

NO. A sufficiently high proportion of the population must be immune, but not everyone needs to be vaccinated.

What is one nuance of herd immunity? Hint: differences based on disease.

More contagious diseases require a higher proportion of the population to be immune.

• Measles: One infected person can infect approximately 16–18 people in a fully susceptible population.

• Influenza: One infected person can infect approximately 2–3 people under comparable simplified assumptions.

Explain why Vaccination is a Contentious Public Health Issue

• Individual rights vs. community protection: Vaccination requirements can conflict with beliefs about bodily autonomy and personal freedom.

• Vaccine hesitancy and misinformation: Concerns about vaccine safety, effectiveness, side effects, and misinformation can create distrust.

• Religious and cultural beliefs: Some individuals oppose vaccination based on personal or religious beliefs.

• Political polarization: Vaccination policies have become politically divisive, particularly following COVID-19.

• Medical mistrust: Historical mistreatment and distrust of health institutions can influence vaccination decisions.

• Invisible when succesful: when vaccines work they are invisible

• Access barriers: Cost, transportation, availability, and medical eligibility can prevent vaccination.

Describe current vaccination trends throughout Michigan

• Childhood vaccination rates in Michigan have been declining, reaching approximately a 10-year low.

• School vaccination exemption rates have increased:

  • 2015: 3.1%

  • 2024: 6.2%

  • 2025: 7.1%

What is Michigan’s kindergarden vaccine exemption rate and how does it compare to national average

• Kindergarteners had a 7.7% exemption rate in 2025.

• Michigan's kindergarten exemption rate exceeds the national average of 4.2% for 2025–26.

What are the Geographic variations in children’s vaccination rate in Michigan?

• Urban/suburban areas: Generally higher vaccination rates and fewer exemptions.

  • Ann Arbor, Novi, Portage, and East Grand Rapids had vaccination completion rates near 95%.

• Northern/rural areas: Generally lower vaccination rates and higher exemptions.

  • Lapeer, Howell, and North Branch had double-digit kindergarten exemption rates.

How do vaccination rates vary between different schools in Michigan?

School Differences:

• Public schools: 90% fully immunized.

• Private schools: 80.9% fully immunized.

• Some online schools have particularly high exemption rates.

What factors are contributing to declining vaccination rates?

• Increased vaccine hesitancy and misinformation following COVID-19.

• Political and cultural influences.

• Conflicting vaccination guidance.

• Vaccination access barriers and exemption policies.

Characterize the role of local health department in promoting vaccination

Most local health departments (LHD) administer vaccinations

LHDs also build trust, understand local context and barriers to vaccination, and combat misinformation

• Vaccine administration: 90% of LHDs provide vaccinations directly to children and adults, often at no cost, especially benefiting uninsured and underserved populations.

• Improve accessibility: Offer mobile clinics, flexible hours, and nontraditional vaccination locations; partner with schools, pharmacies, health care providers, and community organizations.

• Build community trust: Develop relationships with community leaders and use culturally appropriate messaging to increase vaccine confidence.

• Combat misinformation: Provide accurate information, translate educational materials, and address vaccine hesitancy.

• Respond to outbreaks: Coordinate vaccination efforts during outbreaks and respiratory virus seasons.

• Implement national policies: Adapt federal vaccination recommendations to local community needs.

describe LDHs unique contributions to vaccination

Unique Contributions of LHDs:

• Understand community-specific barriers, including transportation, cultural differences, political environments, and health care access.

• Have established relationships with trusted local leaders and organizations.

• Can tailor vaccination strategies to underserved or hesitant populations.

• Build trust before outbreaks occur, making public health responses more effective.

Since millions of bacteria (most harmless) inhabit the human body scientists developed a set of rules that could be used to prove an organism caused a specific disease: called Koch’s postulates. Whar are these postulates?

1. The organism must be present in every case of the disease.

2. The organism must be isolated and grown in the laboratory.

3. When injected with the laboratory-grown culture, susceptible test animals must develop the disease.

4. The organism must be isolated from the newly infected animals and the process repeated

*Used historically to establish whether a specific microorganism causes a disease.

*Some infectious diseases, particularly viral diseases, do not satisfy the original postulates.

What are some challenges facing Local Health Departments (LDH)

• Funding shortages: Depend heavily on federal and state funding, making programs vulnerable to funding cuts.

• Workforce shortages: In 2023, LHDs averaged only six full-time staff members dedicated to immunization.

• Inconsistent national guidance: Changing recommendations and conflicting policies create confusion, decrease public trust, and can reduce vaccine uptake.

What are some reasons someone cannot or will not get vaccinated?

Do not meet vaccine eligibility requirements

Allergies

Medically vulnerable

Medical mistrust (due to historical factors; misinformation)

Access issues (vaccine availability; cost)

What populations are involved in a study usually?

• Target population: the group you ideally want to generalize results to

• Source population: the specific individuals from which a representative sample will be drawn

• Study population: the group you can get access to (the group you can realistically generalize results to)

• Sample: the group who actually ends up in your study

Explain how a study population is identified, moving from the target population to the sample

Researchers move from a broad target population to a smaller group of actual participants. The sample should ideally be representative of the target population.

What is a target population?

the group you ideally want to generalize results to

What is a source population?

the specific individuals from which a representative sample will be drawn

What is a study population?

the group you can get access to (the group you can realistically generalize results to)

What is a sample?

the group who actually ends up in your study

Distinguish Incidence & Prevelance

• Incidence = NEW cases over time.

• Prevalence = ALL existing cases at a point in time.

• Incidence helps measure the risk of developing a disease.

• Prevalence helps measure how widespread a disease is.

What is Incidence?

• Number of NEW cases of a disease that develop in a population over a specified period.

• Measures the occurrence of new disease.

• Expressed as a rate or measure of risk over time.

• Example: 50 people developed diabetes in a town during 2025.

What is Prevelance?

• Number or proportion of ALL EXISTING cases of a disease in a population at a given point in time.

• Includes both new and preexisting cases.

• Usually expressed as a percentage.

• Example: 9% of U.S. adults currently have diabetes.

Identify the 4 different studies we learned.

Cross-Sectional Study (Observational)

Case-Control Study (Observational)

Cohort Study (Observational)

Randomized Controlled Trial (RCT) — Experimental