Interactive population of 120 people showing how descriptive, case-control, cohort and intervention studies count incidence and prevalence
Same 120 people, four study designs, four different levels of proof
Nobody has ever randomly assigned people to smoke for forty years, yet smoking causing lung cancer is one of the most certain facts in medicine. The certainty came from epidemiology: counting disease across whole populations, comparing groups, and knowing exactly what each study design can and cannot claim. Move through the four designs with the same 120 people and watch where the cases gather, then choose incidence or prevalence to see which count each design reads.
Four designs, one populationDescriptive
Change the study design and watch the 120 dots regroup. Predict first: at which design does the cause tile stop saying No?
Which count lights up
Study designDescriptive
DescriptiveCase-controlCohortIntervention
Incidence, year 5
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Can show cause?
No
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Know This
Prevalence counts who has the disease now, incidence counts who newly gets it in a period, and only a study that assigns the exposure at random can show cause.