Study Designs 2.0 Flashcards
PICO vs PECO
All designs P/O
Analytic experiments have I(intervention)/E(exposure) and C(comparison)
When were outcomes determined?
1) Before exposure was determined
- -> case-control (often retrospective)
2) At the same time as exposure
- -> cross-sectional study
3) Some time after exposure
- -> cohort study (prospective)
Case-control studies
• Cases with the disease and a group
of controls without the disease
• Comparison of frequency
• Usually conducted retrospectively
Cross-sectional studies
• Sample of the population (individual animals) is taken at one point in time and is
examined for the presence of the outcome (e.g.disease) and the exposure status regarding to risk factors
Cohort studies
• Selection of two groups of non-diseased animals, – one group exposed to a
factor postulated to be a risk factor for a disease and another group unexposed to the factor
• They are followed over time and their change in disease status (outcome) is
recorded (prospective)
Case-control Studies
Cases (diseased): Exposed or not exposed
Cases (control): Exposed or not exposed
Cohort Studies
1) Identify study subjects
2) Classify exposure status
- Exposed
- Not exposed
3) Exposed
- Case
- Non-case
4) Not Exposed
- Case
- Non-case
Evidence Pyramid (7)
1) Metaanalysis
2) Systematic review
3) Randomised controlled trial
4) Controlled trial without randomisation
5) Observational study (cohort,
case-control or cross sectional)
6) Case series / case report
7) Laboratory studies (e.g. studies in
alternative species), Expert opinion
Narrative Review
– No specific methods are used for selecting sources of evidence
– More susceptible to unrepresentative reporting of evidence
Systematic review
– Relevant studies are systematically identified, appraised and summarized using explicit and reproducible methods (e.g.
search terms, databases)
Meta-analysis
– Results from all relevant studies are analysed statistically to
give an overall summary result
