How health research is reviewed
Research moves through stages. Early work uses cell and animal studies to explore how something behaves. Those results help generate questions, but they do not show what happens in people.
Study types, from strongest to weakest for questions about people
- Meta-analysis: a systematic review that combines results quantitatively.
- Systematic review: a structured search of the literature with critical appraisal.
- Randomized controlled trial: participants are randomly assigned to an experimental or control group and followed over time.
- Cohort study: two groups are followed forward to see who develops the outcome.
- Case-control study: people with an outcome are compared with people without it, looking back at prior exposure.
- Case series: a report on a group of patients with an outcome, with no control group.
At the base are non-human animal and laboratory studies, which occupy the lowest level of evidence.
When you read a headline
Look for the study type, the number of participants, who funded it, and whether it was peer reviewed.
Source: UC Davis Library, "Levels of Evidence." guides.library.ucdavis.edu
Educational content. Not medical advice.