Systematic reviews can often provide the best evidence. They research findings in thorough systematic literature searches. But:
Primary Studies
If a current systematic review isn't available, go to primary studies e.g. papers directly from the researcher who conducted the study. The table below lists optimal study methodologies for the main types of questions.
Question | Best Research Design for Question |
Therapy (Treatment) | Randomised Controlled Trial (RCT) |
Prevention | RCT or Prospective Study |
Diagnosis | RCT or Cohort Study |
Prognosis (Forecast) | Cohort Study and/or Case-Control Series |
Etiology (Causation) | Cohort Study |
Meaning | Qualitative Study |
Note that the Clinical Queries filter available in CINAHL/Medline matches the question type to studies with appropriate research designs.
When searching primary literature, look first for reports of clinical trials that used the best research designs. Remember as you search, though, that the best available evidence may not come from the optimal study type. For example, if treatment effects found in well designed cohort studies are sufficiently large and consistent, those cohort studies may provide more convincing evidence than the findings of a weaker RCT.