Epidemiology Exam 2: Study Designs, Measures of Association, and Social Determinants

Comprehensive vocabulary flashcards covering descriptive epidemiology measures, population pyramids, social determinants of health, observational and experimental study designs, and measures of association.

Descriptive Epidemiology

A major class of epidemiology that systematically characterizes disease and health-related states by person, place, and time without manipulating variables.

Analytic Epidemiology

Studies conducted to test causal hypotheses and determine the strength of association between an exposure and an outcome without researcher interference.

Exploratory Study Design

A study design where an investigator actively manipulates the exposure variable and uses control groups.

Rate

A mathematical ratio consisting of a numerator and a denominator in which time forms an explicit part of the denominator.

Ratio

The mathematical value obtained by dividing one quantity by another quantity.

Proportion

A count relative to the total size of the group where the numerator is part of the denominator, possessing a range from $0$ to $1$, often expressed as a percentage.

Crude Rate

The actual, unadjusted frequency of an event (such as raw counts of deaths or illnesses) observed in a total population.

Adjusted Rate

A summary rate transformed by statistical procedures to remove the confounding effects of demographic differences (such as age or sex) to permit unbiased comparisons between populations.

Incidence

A measure reflecting the number, speed, or risk of new cases of a disease or condition developing in a population at risk over a specified time period.

Prevalence

A measure of the total burden of existing cases (both preexisting and newly diagnosed) of a disease or condition present in a defined population at a given time.

Point Prevalence

The proportion of a population with a condition at a single, specific moment in time; calculated as: $\text{Point Prevalence} = \frac{\text{Number of persons ill}}{\text{Total number in the group}} \times \text{multiplier}$.

Period Prevalence

The proportion of a population with a condition at any point during a defined span of time; calculated as: $\text{Period Prevalence} = \frac{\text{Cases present at start} + \text{New cases during period}}{\text{Average population during the period}} \times 100$.

Attack Rate (AR)

A specialized form of incidence proportion used for short-term, localized outbreaks (e.g., foodborne infections), calculated as: $AR = \frac{\text{Number ill}}{\text{Total exposed (Ill} + \text{Well)}} \times 100$.

Population Pyramid

A specialized double bar graph that visualizes the distribution of a population categorized simultaneously by age group cohorts and biological sex.

Population Pyramid Shapes (Stages 1–4)

Demographic profiles across stages: Stage 1 (early expansive triangle with concave base), Stage 2 (late expansive triangle with straight sides), Stage 3 (stationary beehive/tombstone shape), and Stage 4 (contractive/inverted urn or kite shape).

Stage 1 Population Pyramid (Expansive - Early)

A pyramid with a classic triangle shape, very wide concave base, and sharply tapered top, driven by high birth rates, very high death rates, and low life expectancy.

Stage 2 Population Pyramid (Expansive - Late)

A broad triangular pyramid with straighter sides and expanding middle cohorts, driven by sustained high birth rates and dropping death rates due to sanitation and basic medicine.

Stage 3 Population Pyramid (Stationary)

A beehive or "tombstone" shaped profile with convex, straight sides where birth rates decline to balance low death rates, resulting in slow or stable population growth.

Stage 4 Population Pyramid (Contractive / Inverted)

A top-heavy, urn-shaped or "kite" profile with a base narrower than the middle cohorts, driven by sub-replacement birth rates, very low death rates, high life expectancy, and an aging population.

Acculturation

The gradual process whereby immigrants adopt the cultural traits, behaviors, and dietary patterns of their host nation, altering their baseline disease profiles.

Social Gradient in Health

The empirical observation that individuals of lower socioeconomic or income status experience progressively worse health outcomes across continuous increments of disadvantage.

Cyclic Fluctuations

Recurrent, periodic increases and decreases in disease frequency over the course of years or seasons (e.g., seasonal peaks in influenza, common colds, and RSV).

Point Epidemic

An outbreak characterized by the simultaneous exposure of a susceptible group to an infectious or toxic vehicle from a single common source over a brief window of time.

Secular Time Trends

Gradual, long-term changes or shifts in the morbidity and mortality rates of a disease occurring over many years or decades.

Temporal Clustering

An unusual concentration or grouping of health-related events that occur closely together in time.

Spatial Clustering

An unusual concentration or grouping of health-related events that occur closely together in geographic location.

Social Epidemiology

The branch of epidemiology dedicated to investigating the social distribution and social determinants of a broad spectrum of physical and mental health states.

Five Domains of Social Determinants of Health (SDOH)

The primary social factors shaping population wellness: Education Access and Quality, Health Care Access and Quality, Neighborhood and Built Environment, Social and Community Context, and Economic Stability.

Social Inequality

Measurable, empirical disparities in resource allocation, power, or health outcomes observed across population groups, representing what is without moral evaluation.

Social Inequity

A subset of social inequalities that are judged to be unjust, unfair, systemic, and preventable, stemming from institutional policies and structural discrimination.

Ecologic Study (Correlational Study)

A descriptive design comparing variables of interest at the aggregate population level where the unit of observation and statistical analysis is the group rather than the individual.

Ecological Fallacy

A methodological bias that occurs when an association observed between variables at an aggregate group level is erroneously inferred to exist at the individual level.

Case Report

A descriptive study documenting the clinical profile and history of a single patient presenting with an unusual, rare, or noteworthy health event.

Case Series

A descriptive study aggregating and summarizing the clinical findings and shared characteristics of a group of patients presenting with the same disease in medical facilities.

Cross-Sectional Survey

An observational prevalence study that gathers exposure and disease data simultaneously from individual participants at a single period of observation.

Observational Study

A research design wherein investigators record, observe, and measure participants in their natural settings without manipulating independent exposure variables.

Experimental Study

A research design wherein investigators actively introduce an exposure or intervention and employ randomization and control groups to establish cause-and-effect relationships.

Quasi-Experimental Study

A research design involving manipulation of an intervention where study participants are assigned to groups without random assignment, relying instead on pre-existing conditions or settings.

Case-Control Study

An observational analytic design that selects subjects based on the presence (cases) or absence (controls) of an outcome and ascertains exposure history retrospectively.

Cohort Study

An observational analytic study that selects a disease-free population at risk, classifies them by exposure status, and tracks them longitudinally over time to document incident outcomes.

Prospective Cohort Study

A cohort design that identifies exposure status in the present baseline and follows subjects forward into the foreseeable future to measure the emergence of disease.

Retrospective Cohort Study

A cohort design conducted in the present that utilizes historical records to reconstruct past exposure levels at a baseline point in the past and determines subsequent disease outcomes.

Historical Prospective Cohort Study

A hybrid cohort design that establishes baseline exposures using past historical records and subsequently follows the cohort forward into prospective future observation points.

Loss to Follow-Up

A limitation in longitudinal studies occurring when participants cease communication, move, or drop out before the study investigation is completed.

Single-Blind Protocol

A blinding procedure in clinical trials where the research subject is kept unaware of whether they are assigned to the intervention or control group.

Double-Blind Protocol

A clinical trial design in which neither the study participants nor the investigating researchers know who is receiving the active intervention versus the placebo.

Triple-Blind Protocol

A clinical trial procedure where the study subjects, the clinical investigators, and the data analysts are all kept unaware of group treatment assignments.

Phase 1 Clinical Trial

The introductory trial phase testing a drug or vaccine on fewer than $100$ individuals to assess initial human tolerance, biological actions, and safety.

Phase 2 Clinical Trial

A trial phase expanding intervention testing to a target group of $100$ to $200$ individuals to establish early efficacy and safe therapeutic dosage.

Phase 3 Clinical Trial

The main confirmatory trial phase testing an intervention in a large cohort from the target population to definitively establish therapeutic efficacy and safety prior to approval.

Phase 4 Clinical Trial

Post-marketing surveillance studies conducted after regulatory approval to monitor long-term therapeutic effectiveness and detect rare adverse effects across the general population.

Community Trial (Cluster RCT)

An experimental trial in which intact aggregate units (such as towns, schools, or clinics) rather than individuals are randomized to receive environmental or educational interventions.

Clinical Equipoise

A state of genuine ethical uncertainty within the scientific community regarding whether an experimental therapy offers superior benefit compared to the control regimen.

Null Hypothesis ($H_0$)

A statistical hypothesis positing that there is no true difference, effect, or association between the exposure and the health outcome being studied.

Alternative Hypothesis ($H_1$)

A statistical hypothesis asserting that a true difference, effect, or association exists between the exposure and the health outcome being studied.

Absolute Measures of Association

Epidemiological parameters calculated by taking the mathematical difference between two measures of disease frequency (such as risk difference or rate difference).

Relative Measures of Association

Epidemiological parameters calculated as the ratio of two measures of disease frequency (such as Relative Risk or Odds Ratio) to quantify the strength of an association.

Odds Ratio (OR)

The primary measure of association in case-control studies, defined as the odds of exposure among diseased cases divided by the odds of exposure among non-diseased controls.

Relative Risk (RR)

The ratio of the risk of disease in the exposed cohort to the risk of disease in the unexposed cohort; calculated as: $RR = \frac{\text{Risk in Exposed}}{\text{Risk in Unexposed}} = \frac{A / (A + B)}{C / (C + D)}$.

Relative Rate Ratio (Rate Ratio / IRR)

A measure comparing the incidence rate of an outcome over person-time in an exposed group to that of an unexposed group, expressed as: $\text{Rate Ratio} = \frac{\text{Incidence Rate in Exposed}}{\text{Incidence Rate in Unexposed}} = \frac{A / PT_{\text{exposed}}}{C / PT_{\text{unexposed}}}$.

Attributable Risk (AR / Risk Difference)

The absolute excess disease risk caused by an exposure, calculated as: $AR = \text{Risk in Exposed} - \text{Risk in Unexposed} = \left(\frac{A}{A + B}\right) - \left(\frac{C}{C + D}\right)$.