Epidemiology questions often test whether you can choose the right measure for a study, calculate it correctly and explain what it does—and does not—show. A useful flashcard deck should make you retrieve a definition or calculation, not just recognise a term.
Work through the cards one at a time. Read each question and say your answer before checking the answer shown. Then grade your recall: choose Again if you could not answer, Hard if it took effort or was incomplete, Good if you answered correctly, and Easy if the answer came promptly and clearly. Be strict: remembering a formula but mixing up its numerator is not a correct answer.
The first card below is face-up to show the review controls. Continue through the deck, checking each answer and grading it before moving on. Here is a MySummaries epidemiology deck built around the measures and decisions candidates commonly need to distinguish:
Cards — Epidemiology foundations18 due
How do you calculate cumulative incidence (risk) over a specified period?
New cases during the period ÷ the number of people at risk at the start of the period. State the period. This assumes the denominator represents those at risk of becoming a case.
All 18 cards
How do you calculate cumulative incidence (risk) over a specified period?New cases during the period ÷ the number of people at risk at the start of the period. State the period. This assumes the denominator represents those at risk of becoming a case.
What does an incidence rate use in its denominator?Person-time at risk. Incidence rate = new events ÷ total person-time at risk.
How is point prevalence calculated?All existing cases at a specified point in time ÷ the population at that point in time.
How do you calculate the risk ratio (relative risk) in a cohort study?Risk in the exposed group ÷ risk in the unexposed group over the same follow-up period.
What does a risk ratio of 1 mean?The observed risk is equal in the two groups. It indicates no association on the relative-risk scale, not proof that no causal effect exists.
How is a risk difference calculated?Risk in the exposed group − risk in the unexposed group. It is an absolute difference in risk over the specified period.
How do you calculate an odds ratio in a case-control study?Odds of exposure among cases ÷ odds of exposure among controls. For a 2 × 2 table with cells a, b, c, d, OR = ad ÷ bc.
When can an odds ratio approximate a risk ratio?When the outcome is rare in the population from which the study groups arise; the approximation is not reliable for common outcomes.
What is the defining sampling feature of a case-control study?Participants are selected according to outcome status (cases and controls), and prior exposure is compared between the groups.
Which measure can a cohort study estimate directly when follow-up is complete?Incidence, including cumulative incidence (risk), because participants are followed from being at risk to outcome or the end of follow-up.
What does a cross-sectional study usually measure?Exposure and outcome at one point or period in time; it can estimate prevalence but usually cannot establish which came first.
Write the formula for sensitivity.True positives ÷ (true positives + false negatives). It is the proportion of people with the condition who test positive.
Write the formula for specificity.True negatives ÷ (true negatives + false positives). It is the proportion of people without the condition who test negative.
Write the formula for positive predictive value (PPV).True positives ÷ (true positives + false positives). PPV is the proportion of positive test results that are true positives.
Why does PPV change when disease prevalence changes, even if sensitivity and specificity stay constant?PPV depends on how common the condition is in the tested population. With lower prevalence, false positives make up a larger share of positive results.
How is the positive likelihood ratio calculated?LR+ = sensitivity ÷ (1 − specificity). It describes how much more likely a positive result is in someone with the condition than in someone without it.
What is a confounder in a causal analysis?A factor associated with the exposure and outcome that is not on the causal pathway between them; it can distort the estimated exposure–outcome association.
What is the ecological fallacy?Inferring that an association observed between groups must also hold for individuals within those groups.
That is a MySummaries deck, filled with epidemiology material. Yours is written from your own notes. Start free
Check the distinctions, not just the definitions
After the first pass, review any card graded Again or Hard. Say the formula from memory, including its denominator, then explain the result in plain language. For example, incidence rate uses person-time; cumulative incidence uses people at risk at the start. They are related measures of new disease occurrence, but they are not interchangeable.
Pay particular attention to the different denominators for diagnostic-test measures. Sensitivity starts with people who have the condition; specificity starts with people who do not. PPV starts with positive test results. If you can name the denominator before writing a formula, you are less likely to swap the measures under time pressure.
Study-design cards also test what can be inferred. A cohort can measure incidence because people are followed over time. A case-control study begins with outcome status and compares earlier exposure, so its usual association measure is the odds ratio. A cross-sectional study can estimate prevalence, but measuring exposure and outcome at roughly the same time often leaves their temporal order unclear.
Finally, keep association separate from causation. A ratio of 1 is a statement about the observed comparison on that scale; it does not prove the absence of a causal effect. Likewise, adjustment for a confounder does not automatically remove every source of bias. The study design, measurements, selection of participants and assumptions all matter.
The must-not-miss core
Use this short checklist after you have worked through the deck. Try to state each item without looking back at the cards. If a formula is shaky, return to its card rather than memorising the checklist as a paragraph.
Must not miss coreEpidemiology foundations
Cumulative incidence = new cases during a stated period ÷ people at risk at the start; incidence rate = new events ÷ person-time at risk.
Prevalence counts existing cases; incidence counts new cases or events. Always identify the time period and denominator.
Cohort studies follow exposure groups and can estimate incidence; case-control studies select by outcome and commonly use an odds ratio; cross-sectional studies estimate prevalence but usually cannot establish temporality.
Risk ratio compares risks; risk difference subtracts risks. Confounding distorts an exposure–outcome association; group-level associations do not necessarily describe individuals.
Turn repeated errors into a small review task
When a formula or distinction is missed repeatedly, make the next review specific. Do not write “revise epidemiology”; write a question that forces the exact retrieval you failed. For example, if you keep using all participants as the sensitivity denominator, practise naming the population represented by each test measure.
A useful remediation card names the error and asks for one answer. Here is an example for a candidate who has twice confused sensitivity with PPV:
Remediation tray
You lost this mark twice: sensitivity and PPV are both about positive results, but what is the denominator for each, and which one depends on prevalence?
Add cardDismiss
Answer the tray question aloud, then return to the relevant cards and grade them honestly. If the confusion persists, draw a 2 × 2 table and label true positive, false positive, false negative and true negative before writing any formula. That simple step makes the denominator visible and helps you select the right measure for the question.
How MySummaries helps
MySummaries builds flashcards from a revision board made from your own PDFs, slides or photographed notes, then schedules cards for spaced review. You can use the same board to generate written practice and other study activities from your material. Open MySummaries
Studying epidemiology? Make your epidemiology deck from your own notes. MySummaries writes the cards from your board and schedules each one by how well you knew it. The free plan makes your first 20 — no payment details, nothing expires.