Study designs
Descriptive, case-control, cohort, cross-sectional, ecological studies and clinical trials.
30 pages
Concept
- BlindingHiding who receives which treatment, so that the expectations of patient, doctor or assessor do…
- Intention-to-treat analysisEach patient is analysed in the group chance assigned them to, even if they never received or…
- Interim analyses and early stoppingLooking at a trial's data before it ends lets it stop for clear benefit, harm or futility, but…
- MatchingChoosing controls who resemble the cases in age, sex or another factor, so that factor cannot…
- Phases of clinical trialsA new medicine moves through phases: safety in a few volunteers first, then efficacy in…
- Pragmatic and explanatory trialsAn explanatory trial asks whether something can work under ideal conditions; a pragmatic one…
- Randomisation and allocation concealmentChance draws up the list of who goes to each group; concealment stops anyone from seeing it…
- Real-world evidence and comparative effectivenessUses data from everyday care (registries, health records, billing) to see how treatments perform…
- Study designs: how to tell them apartThree questions name almost any design: who assigned the exposure, is there a comparison group…
Study design
- Case report and case seriesOne or several patients with something new or rare are described in detail
- Case-cohort studyInside a large cohort, all cases plus a random subcohort chosen at the start are analysed; the…
- Case-control studyStart with sick people (cases) and healthy people (controls) and compare how many were exposed…
- Case-crossover designOnly cases are studied: each person is compared with themselves, just before the event and at…
- Cluster randomised trialWhole groups (schools, clinics, neighbourhoods) are randomised instead of people, because the…
- Cohort studyExposed and unexposed people are followed over time and investigators count who falls ill
- Community trialA prevention programme is tested in whole communities (towns, neighbourhoods) and compared with…
- Cross-sectional studyA snapshot: exposure and disease are measured at the same time in a sample
- Crossover trialEach patient gets both treatments, one after the other in random order: they are their own…
- Ecological studyIt compares whole groups (municipalities, countries, years), not people
- Factorial trialOne trial answers two questions: two interventions are randomised at once, alone, together or…
- Family, twin and adoption studiesTo weigh the role of genes, researchers compare relatives, identical with fraternal twins, and…
- Linkage and genetic association studies (GWAS)They look for the region or variant of the genome that travels with a disease: in families…
- Migrant studiesIf people who move take on the rates of their new country, the cause lies mostly in the…
- N-of-1 trialA trial in a single patient: two treatments alternate several times, in random order, to find…
- Nested case-control studyInside a cohort that is already followed, those who fall ill and a few controls are picked, and…
- Quasi-experimental designsThey evaluate a programme or policy without randomisation, using comparisons over time or with…
- Randomised controlled trialChance decides who gets the intervention and who gets the control
- Superiority, equivalence and non-inferiority trialsA better treatment is not always the goal: sometimes it is enough to show that a simpler or…
- Uncontrolled studies and historical controlsComparing today's patients with past ones, or with themselves before treatment, tends to…
Measure
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← Epidemiology, biostatistics and public health
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Representative model, for educational purposes only.