Public Health Foundations and Epidemiology

Flashcards covering key public health definitions, core functions, levels of prevention, epidemiology basics, disease frequency measures, and observational study designs.

How did Charles-Edward A. Winslow define public health in 1920?

The science and the art of preventing disease, prolonging life, and promoting physical health and efficiency through organized community efforts.

What are the three core functions of public health?

Assessment, Policy development, and Assurance.

What are the key differences between clinical medicine and public health regarding typical unit, aim, and common tools?

Clinical medicine focuses on the individual patient, aims to diagnose and treat, and uses exams and therapies. Public health focuses on the population, aims to prevent and protect, and uses data, policy, and interventions.

What are the five core disciplines of public health and their core contributions?

1. Epidemiology: Patterns, comparisons, causes
2. Biostatistics: Measurement and uncertainty (quantitative)
3. Social Behavioral Sciences: Behavior, institutions, inequality (qualitative)
4. Environmental health: Hazards and exposure
5. Policy and management: Collective decisions and delivery

What are the main aims and timings of primary, secondary, and tertiary prevention?

Primary prevention acts before disease onset to reduce exposure or susceptibility. Secondary prevention acts during early or asymptomatic disease to detect and act sooner at onset. Tertiary prevention acts after established disease or injury to limit complications and restore function.

What are examples of primary, secondary, and tertiary prevention for motor-vehicle injuries?

Primary prevention (before crash): Road design, speed management, traffic signals, and impaired-driving laws. Secondary prevention (during crash): Seat belts, airbags, child restraints, and crashworthy vehicle design. Tertiary prevention (after injury): Rapid 911 response, trauma care, and rehabilitation.

How is epidemiology defined in the lecture course?

Epidemiology studies the patterns of disease occurrence in human populations and the factors that influence these patterns.

What three components comprise the Epidemiologic Triad?

1. Agent: What causes the disease (e.g., virus, bacteria)
2. Host: Where the disease lives or who is affected (e.g., human, animal)
3. Environment: How the agent transfers to the host or the surrounding conditions

What three categories characterize disease distribution in descriptive epidemiology?

Person (who is affected), Place (where it occurs), and Time (when it occurs).

What is the difference between a fixed population and a dynamic population?

A fixed (closed) population has permanent membership (e.g., Vietnam War veterans, individuals born in 2005). A dynamic (open) population has changeable membership as individuals move in and out (e.g., the population of New York City).

What is the distinction between morbidity and mortality?

Morbidity refers to the state of being diseased or unhealthy within a population, while mortality refers to the incidence of death within a population.

What are the definitions of point prevalence, period prevalence, and cumulative lifetime prevalence?

Point prevalence is the proportion of a population with a condition at one specific point in time. Period prevalence is the proportion of a population that had a condition at any time during a specified period. Cumulative lifetime prevalence is the proportion of a population that has ever experienced a condition up to the time of assessment.

What is the general formula for calculating prevalence?

$$\text{Prevalence} = \frac{\text{Number of cases (new and old) present in the population at a specified time}}{\text{Number of persons in the population at that specified time}}$$

What is cumulative incidence and what is its formula?

Cumulative incidence is a measure of disease risk representing the proportion of at-risk individuals who develop the disease during a specified time period: $\text{Cumulative Incidence} = \frac{\text{Sum of number of new cases present at a specified time period}}{\text{Number of persons at risk in the population at that specified time period}}$

How is incidence density (rate) defined and calculated?

Incidence density is the rate at which disease occurs, calculated using person-time units in the denominator: $\text{Incidence Density} = \frac{\text{Sum of number of new cases}}{\text{Persons at risk} \times \text{Time at risk in the population}}$

How do prevalence and incidence relate for chronic incurable diseases versus short-lived curable diseases?

For chronic, incurable diseases (e.g., HIV/AIDS, diabetes), prevalence is greater than incidence ($\text{Prevalence} > \text{Incidence}$). For short-lived, curable diseases or rapidly fatal conditions, incidence is greater than prevalence ($\text{Incidence} > \text{Prevalence}$).

What are crude mortality rate, disease-specific mortality rate, and age-specific mortality rate?

Crude mortality rate is the total deaths from all causes divided by the total population at midyear. Disease-specific mortality rate is deaths due to a specific cause divided by the population at midyear. Age-specific mortality rate is deaths among a specific age group divided by the population in that age group at midyear.

How are infant mortality rate and case fatality rate defined?

Infant mortality rate is the number of deaths among infants $< 365$ days old compared to the total number of live births. Case fatality rate is the proportion of individuals who die from a disease among all those diagnosed with that disease.

What is the difference between an exposure and an outcome in health research?

An exposure is the independent variable ($x$) or risk factor that might influence a result. An outcome is the dependent variable ($y$) or the disease, condition, behavior, or health event being studied.

What distinct questions do descriptive epidemiology and analytic epidemiology address?

Descriptive epidemiology asks who, where, and when to identify disease patterns and generate hypotheses. Analytic epidemiology asks why and how to compare groups, test hypotheses, and determine the strength of exposure-outcome associations.

What is an observational study and why is it used instead of an experimental study?

An observational study is research where investigators record data and measure outcomes without assigning or controlling exposures. It is used because experimental assignment to harmful exposures (e.g., smoking, air pollution, poverty) would be unethical, impractical, expensive, or too time-consuming.

What is a cross-sectional study design?

A cross-sectional study measures both exposure and outcome at approximately the same point in time, providing a snapshot of a population to estimate prevalence.

What are the main strengths and limitations of cross-sectional studies?

Strengths: Relatively quick and inexpensive, provides a snapshot of population health, estimates prevalence, helps identify public health needs. Limitations: Temporal order between exposure and outcome is unclear, reverse causation is possible, and incidence cannot be calculated directly.

What is a cohort study design and what is its starting point?

A cohort study begins by classifying participants based on exposure status (exposed vs. unexposed) and follows them over time to observe and compare who develops the outcome.

What is the difference between a prospective cohort study and a retrospective cohort study?

A prospective cohort study measures exposure at baseline and follows participants forward in calendar time into the future to record new outcomes. A retrospective cohort study uses existing historical records (e.g., employment or medical records) to determine past exposures and links them to outcomes that have already occurred.

What is the formula for calculating Risk Ratio (Relative Risk) in a cohort study?

$$\text{Risk Ratio (RR)} = \frac{\text{Risk of disease among exposed}}{\text{Risk of disease among unexposed}} = \frac{\frac{a}{a+b}}{\frac{c}{c+d}}$$

What are the main strengths and limitations of cohort studies?

Strengths: Establishes temporal sequence (exposure precedes outcome), directly measures incidence, calculates relative risk, can study rare exposures. Limitations: Requires significant time and money, vulnerable to loss to follow-up, inefficient for rare outcomes.

What is a case-control study design?

A case-control study begins by selecting participants based on outcome status (cases with disease, controls without disease) and examines their previous exposure histories.

What is the formula for calculating the Odds Ratio (OR) in a case-control study?

$$\text{Odds Ratio (OR)} = \frac{\text{Exposure odds among cases}}{\text{Exposure odds among controls}} = \frac{\frac{a}{c}}{\frac{b}{d}} = \frac{a \times d}{b \times c}$$

What are the main strengths and limitations of case-control studies?

Strengths: Highly efficient for rare diseases, faster and less expensive than cohort studies, requires fewer participants, can examine multiple previous exposures. Limitations: Cannot directly calculate incidence or prevalence, vulnerable to selection bias and recall bias, inefficient for rare exposures.