Introduction to Study Designs

What are the two broad categories of epidemiologic studies?

Descriptive and analytic studies.

What does descriptive epidemiology primarily deal with?

The distribution of disease, including estimating disease frequency and time trends.

What does analytic epidemiology primarily deal with?

The determinants of disease in order to test etiologic hypotheses and establish or reject causal links.

In descriptive studies, how are exposure and outcome assessed?

They are assessed together.

What is an alternate name for a cross-sectional study?

Survey or prevalence study.

What are alternate names for a cohort study?

Prospective, prospective cohort, longitudinal, follow-up, or incidence study.

What is an alternate name for a case-control study?

Retrospective study.

What are alternate names for an experimental study?

Randomized controlled trial, field trial, community trial, or intervention study.

What is an alternate name for an ecological study?

Correlation study.

What do ecological studies use as the unit of analysis?

Groups or populations, such as countries, states, counties, or census tracts.

What is the ecological fallacy?

A potential problem where people with the outcome may not actually be the ones with the exposure.

How do observational studies differ from experimental studies regarding conditions?

Observational studies examine conditions that already occurred or will occur anyway, while experimental studies put conditions under direct control of the investigator.

What study design begins with diseased cases and non-diseased controls to compare past exposures?

Case-control study.

What study design measures exposure and outcome at the same time?

Cross-sectional study.

What study design identifies disease-free individuals, classifies their exposure, and follows them over time?

Cohort study.

In a cohort study, how is the risk ratio calculated?

By dividing the risk in the exposed by the risk in the unexposed.

When are incidence rates particularly good to use in cohort studies?

When there is loss to follow-up.

What are two major disadvantages of cohort studies?

They are inefficient for studying rare diseases and can require large sample sizes or be expensive.

What major temporal advantage do cohort studies have?

There is a clear temporal relationship ensuring the exposure came before the outcome.

What is information bias in cohort studies?

Bias that occurs when information quality is not high and comparable across exposed, unexposed, diseased, and non-diseased groups.

How does a randomized trial differ from an observational cohort study?

Individuals are randomized to be exposed or unexposed rather than having their exposure merely observed.

Why is randomization considered the gold standard in studies?

Because it is expected to balance risk factors for disease in both the exposed and unexposed groups.

What is internal validity in a clinical trial?

When the calculated statistic provides a good, unbiased estimate of the parameter in the population without confounding or measurement bias.

What is external validity or generalizability?

The goal of generalizing study results beyond the study population to the broader population.

What is required in order to generalize study results beyond the study population?

An inclusive sampling strategy and good internal validity.

What is confounding in epidemiologic studies?

When two groups of people are not exchangeable.

What is the overarching purpose of blinding patients and providers?

Bias reduction.

How is patient blinding typically achieved in a clinical trial?

With a placebo.

What does provider blinding help avoid?

Subjective assessment and decisions.

What ethical principle requires genuine uncertainty about which treatment is more beneficial?

Equipoise.

Under what circumstance should a clinical trial be stopped earlier than planned?

Once you know for certain that one treatment is better than the other and equipoise no longer exists.

What is the main difference between observational studies and randomized trials?

The presence or absence of randomization of participants into exposure groups.

What type of study examines the association between population-level exposure rates and disease rates?

Ecological study.

What are the two major types of neural tube defects discussed in the lecture examples?

Spina bifida and anencephaly.

What specific exposure was analyzed in the lecture's primary neural tube defect study example?

Folate supplement before pregnancy.