2 Epidemiology Basics Free Online FlashCards

What does epidemiology study?

Epidemiology studies how health-related conditions are distributed across populations, what factors influence them, and how to prevent or control health problems.

Which three dimensions commonly describe health patterns?

Person, place, and time.

What does prevalence measure?

Prevalence is the proportion of a population that has a condition at a specified time or during a specified period. It includes new and pre-existing cases.

How do point and period prevalence differ?

Point prevalence measures cases at a specified time; period prevalence measures cases during a specified period.

How does incidence differ from prevalence?

Incidence measures new cases among people initially at risk; prevalence measures how widespread a condition is.

What is incidence proportion, also called risk?

Incidence proportion, or risk, is the proportion of an at-risk group that develops the condition over a specified period.

What does an incidence rate use in its denominator?

Incidence rate is new cases divided by total person-time at risk. Person-time allows participants to contribute different amounts of observation time.

Exposed risk is $10\%$ and unexposed risk is $5\%$. What is the risk ratio?

The risk ratio is $10\% \div 5\% = 2$. The exposed group had twice the risk.

Exposed risk is $10\%$ and unexposed risk is $5\%$. What is the risk difference?

The risk difference is $10\% - 5\% = 5$ percentage points: five additional cases per 100 people in the exposed group over the period.

Why do case-control studies generally use an odds ratio?

Case-control studies generally use an odds ratio because participants are selected based on outcome status, so researchers cannot directly calculate risk from that selection.

What key limitation can affect a cross-sectional study?

A cross-sectional study measures exposure and health status at one point or over a short period. Because both are measured together, their time order may be unclear.

How does a cohort study help establish time order?

A cohort study groups people by exposure and follows them to compare outcomes. It can estimate incidence and clarify whether exposure preceded the outcome.