Cohort study vs Case-control study
How to tell Cohort study and Case-control study apart when a board question makes them look alike.
Cohort: starts from exposure and follows forward for outcomes (incidence, RR); case-control: starts from outcome and looks back at exposure (OR).
Side by side
Cohort studies start with exposure status and follow forward or backward to compare outcome incidence.
Case-control studies start with disease status and look back for exposure odds, useful for rare diseases.
Cohort studies start with exposure status and follow forward or backward to compare outcome incidence.
Case-control studies start with disease status and look back for exposure odds, useful for rare diseases.
Groups defined by exposure at the start; measures incidence and relative risk; prospective or retrospective.
Groups defined by outcome at the start; looks back at exposure; measures the odds ratio; efficient for rare diseases.
The trap
Cohort starts exposure to outcome; case-control starts outcome to exposure.
The repair move
Before naming the answer, force the stem through the separator: Cohort starts exposure to outcome; case-control starts outcome to exposure.
Try a free question
CoreInvestigators want to study whether a high-saturated-fat diet causes heart disease. They identify 10,000 healthy adults, assess their dietary habits at baseline (5,000 high-fat, 5,000 low-fat diets), and follow them prospectively for 20 years to count cardiovascular events in each group. Which study design is this?
Show answer and explanation
Answer: A. Prospective cohort study. Cohort study starts with EXPOSURE status and follows participants forward in time to measure outcomes. Prospective cohort follows from the present (more reliable but expensive); retrospective cohort uses existing records. Measures incidence and relative risk (RR). Ideal for studying common diseases with adequate event rates and multiple outcomes from a single exposure.
Why the other choices are tempting
- B. Case-control starts with disease status and looks backward for exposures.
- C. Cross-sectional measures exposure and outcome at one point in time.
- D. RCT randomly assigns interventions.
- E. Ecologic studies compare aggregate group data, not individual data.
Flashcards
Tap a card to flip it.
What clue supports Cohort study?
Choose Cohort study when the stem gives this pattern: Cohort studies start with exposure status and follow forward or backward to compare outcome incidence.
What clue supports Case-control study?
Choose Case-control study when the stem gives this contrasting pattern: Case-control studies start with disease status and look back for exposure odds, useful for rare diseases.
Quick answers
What is the fastest way to tell Cohort study from Case-control study?
Cohort: starts from exposure and follows forward for outcomes (incidence, RR); case-control: starts from outcome and looks back at exposure (OR).
What is the key clue for Cohort study?
Cohort studies start with exposure status and follow forward or backward to compare outcome incidence.
What is the key clue for Case-control study?
Case-control studies start with disease status and look back for exposure odds, useful for rare diseases.
What is the common trap with Cohort study vs Case-control study?
Cohort starts exposure to outcome; case-control starts outcome to exposure.