There are four main study types that can be easily applied to practice:
1. Descriptive studies: These include study types such as case studies and case series, and are purely a description of what happened to an individual or group of animals. They are very useful to describe a new emerging disease or a potentially new treatment or technique. They cannot be used to measure risk of disease, frequency of disease, causation of disease or the effectiveness of one treatment as compared to another.
2. Observational studies: These studies include cross-sectional studies, cohort studies and case-control studies. They can provide information about the frequency of diseases (cross-sectional and cohort studies) and risk factors for disease (cross-sectional studies, cohort studies and case-control studies).
3. Interventional studies: Randomised controlled trials (RCTs) are studies that can investigate the comparative effectiveness of medical and surgical interventions. These are the types of study you need if you want to know a treatment works.
4. Evidence synthesis: Methods such as systematic review and meta-analysis can be applied to all kinds of studies and involve bringing similar studies together and looking at their cumulative findings.
For more information on study types, see the free resources at the Centre for Evidence-based Medicine.