Primary: Prevent disease occurrence
Secondary: Early detection of the disease
Tertiary: Reduce disability and complications from the disease
Used for measuring the prevalence of a disease; usually chronic
Advantages: Cheap, easy, and quick
Not appropriate for short-term diseases
A retrospective study
Advantages: Easy, cheap, and simple
Disadvantages: Recall bias, and failure to calculate risk ratio
A prospective study, e.g., Framingham study
Advantages: Used to measure incidence rates of a disease
Disadvantages: Needs a large sample size; time-consuming and expensive.
Patients are divided into two groups:
Experimental: Take a new medication
Control: Take a placebo
Blinding: May be single blind (patient does not know), double blind (patient and investigator do not know), or triple blind (patient, investigator, and analyzer do...