Study Design

This page gives a brief comparison of the advantages and disadvantages of the different types of study.

Advantages:
1. quick and cheap;
2. only feasible method for very rare disorders or those with long lag between exposure and outcome;
3. fewer subjects needed than cross-sectional studies.
Disadvantages:
1. reliance on recall or records to determine exposure status;
2. confounders;
3. selection of control groups is difficult;
4. potential bias: recall, selection.

Advantages:
1. unbiased distribution of confounders;
2. blinding more likely;
3. randomisation facilitates statistical analysis.
Disadvantages:
1. expensive: time and money;
2. volunteer bias;
3. ethically problematic at times.

Advantages:
1. all subjects serve as own controls and error variance is reduced thus reducing sample size needed;
2. all subjects receive treatment (at least some of the time);
3. statistical tests assumeing randomisation can be used;
4. blinding can be maintained.
Disadvantages:
1. all subjects receive plcebo or alternative treatment at some point;
2. washout period lengthy or unknown;
3. cannot be used for treatments with permanent effects.