Study Design

Question 1

Hierarchy of Evidence (Best - Worst)

Answer 1

1. Systematic Reviews and Meta Analysis
2. Randomised control trials
3. Cohort studies
4. • Case-Control studies
   • Cross-Sectional Studies
5. Case Series and Case Reports
6. Editorials and Expert Opinions

Question 2

Case-Control Study Definition, Advantages and Disadvantages

Answer 2

Retrospective, observational study looking at cause of disease. Compares similar participants with disease to controls without
Advantages:
- Good for rare outcomes
- Quicker than cohort or intervention studies (outcome already happened)
- Can investigate multiple exposures
Disadvantages:
- Difficulties finding controls to match with case
- Prone to selection and information bias

Question 3

Cross-sectional Study Definition, Advantages and Disadvantages

Answer 3

Retrospective observational study collects data from a population at a specific point in time ‘snapshot’
Advantages:
- Relatively quick and cheap
- Provide data on prevalence at single point in time
- Good for surveillance and PH planning
Disadvantages:
- Risk of reverse causality (did outcome or exposure come first)
- Cannot measure incidence
- Recall and response bias risk (may miss quick recoveries)

Question 4

Cohort Study Definition, Advantages and Disadvantages

Answer 4

Prospective longitudinal study looking at separate cohorts with different treatments or exposures. Wait to see if diseases occurs.
Advantages:
- Can follow-up group with rare exposure
- Good for common and multiple outcomes -> establish disease risk and cofounders
- Less risk of selection and recall bias
Disadvantages:
- Takes a long time
- People drop out
- Need large sample size, expensive and time consuming

Question 5

Randomised control trials Definition, Advantages and Disadvantages

Answer 5

Prospective study, all participants randomly assigned exposure or control intervention
Advantages:
- Low risk of bias and confounding
- Can infer causality
Disadvantages:
- Time consuming and expensive
- Drop outs
- Inclusion criteria may exclude some populations

Question 6

Ecological study definition

Answer 6

Looks at the prevalence of the disease over time (population data rather than individual)
Can show prevalence and association but not causation