Study Design Flashcards
What are the two types of study designs?
Experimental and observational
What is an experimental study design?
The researcher intervenes to change reality, then observes what happens
What is an observational study design?
The researcher studies what occurs, but does not try to change the subjects being observed
What are the types of experimental studies?
Randomised Control Trial (RCT) and Non-Randomised Controlled Trial (Quasi-Experimental Design)
What are the types of observational studies?
Analytical study (used to test hypotheses) and Descriptive Study (case reports)
What are the types of analytical studies?
Cross-sectional surveys (“snapshot”), Cohort Studies (Prospective) and Case-control studies (retrospective)
What are the strengths of a cross sectional study design?
- Less time-consuming than other designs
- Inexpensive
- Simple
- Ethically safe
What are the weaknesses of a cross sectional study design?
- Establishes association at most, not causality
- Recall bias susceptibility
- Confounders may be unequally distributed
What are the strengths of a cohort study design?
• Ethically safe
• Subjects can be matched at baseline
• Can establish timing and directionality of events
• Eligibility criteria and exposure/outcome
assessments can be standardized
What are the weaknesses of a cohort study design?
• Controls may be difficult to identify
• Exposure may be linked to a hidden confounder
• Blinding is difficult
• Randomisation not present;
• For rare disease, large sample sizes or long follow-up
necessary.
What are the strengths of a case-control study design?
• Quick and cheap
• Only feasible method for very rare disorders or
those with long lag between exposure and
outcome
• Fewer subjects needed than cross-sectional
studies
What are the weaknesses of a case-control study design?
• Reliance on recall or records to determine exposure status
• Confounders - to ensure greater comparability between the
two groups and thereby avoid confounding, controls could
be matched for sex and age to the cases.
• Selection of control groups is difficult
• Potential bias: recall, selection
What are the strengths of a RCT study design?
- Unbiased distribution of potential confounders
- Blinding more likely
- Randomization facilitates statistical analysis
What are the weaknesses of a RCT study design?
- Expensive: time and money
- Volunteer bias
- Ethically problematic at times
What are the strengths of a cross over study design?
• All subjects serve as own controls and error
variance is reduced thus reducing sample size
needed
• all subjects receive treatment
• blinding can be maintained
