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This page gives a brief comparison of the advantages and disadvantages of the
different types of study.
see also Levels
of Evidence
Case-Control Studies
- Advantages:
- 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.
- Disadvantages:
- reliance on recall or records to determine exposure
status;
- confounders;
- selection of control groups is difficult;
- potential bias: recall, selection.
Cross-Sectional Survey
- cheap and simple;
- ethically safe;.
- Disadvantages:
- establishes association at most, not causality;
- recall bias susceptibility;
- confounders may be unequally distributed;
- Neyman bias;
- group sizes may be unequal.
Cohort Study
- Advantages:
- ethically safe;
- subjects can be matched;
- can establish timing and directionality of events;
- eligibility criteria and outcome assessments can be
standardised;
- administratively easier and cheaper than RCT.
- Disadvantages:
- thcontrols 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.
Randomised Controlled Trial
- Advantages:
- unbiased distribution of confounders;
- blinding more likely;
- randomisation facilitates statistical analysis.
- Disadvantages:
- expensive: time and money;
- volunteer bias;
- ethically problematic at times.
Crossover Design
- Advantages:
- all subjects serve as own controls and error variance
is reduced thus reducing sample size needed;
- all subjects receive treatment (at least some of the
time);
- statistical tests assumeing randomisation can be
used;
- blinding can be maintained.
- Disadvantages:
- all subjects receive plcebo or alternative treatment
at some point;
- washout period lengthy or unknown;
- cannot be used for treatments with permanent effects.