In health, evidence is drawn from two main types of research:
|Primary research||New research, carried out in clinical settings, to investigate specific issues or answer questions, e.g. randomised controlled trials.|
|Secondary research||Analysis gathered from primary research, e.g. a systematic review. Secondary research is rated more highly due to the appraisal / review process improving the quality of evidence for decision-making.|
The Evidence Pyramid shows the levels of different types of research - the higher the level, the more rigorous the methodology behind the research - allowing users to weigh the decision-making support potential of the evidence.
|Systematic review that uses quantitative methods to synthesise and summarise the results. [Secondary research]|
|Summary of the medical literature that uses explicit methods to perform a comprehensive literature search and critical appraisal of individual studies and that uses appropriate statistical techniques to combine these valid studies. [Secondary research]|
|Participants are randomly allocated into an experimental group or a control group and followed over time for the variables/outcomes of interest. [Primary research]|
|Involves identification of two groups (cohorts) of patients, one which received the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest. [Primary research]|
|Study which involves identifying patients who have the outcome of interest (cases) and patients without the same outcome (controls), and looking back to see if they had the exposure of interest. [Primary research]|
|Report on a series of patients with an outcome of interest. No control group is involved. [Primary research]|
(Definitions from CEBM)
Read a perspective on a New Evidence Pyramid (2016) from BMJ Evidence-Based Medicine.
Study Types has more on the studies undertaken for primary research.
For more on secondary research, see our Systematic Reviews guide.