What Is a Secondary Outcome?
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A secondary outcome is an additional result measured in a study to answer supporting questions, such as effects on other symptoms, safety or quality of life. Secondary outcomes are defined in advance but are not the main basis for the study's conclusions.
Example
Invented for teaching: In a trial where the primary outcome is blood pressure, secondary outcomes could include body weight, adverse events and patient-reported quality of life at 12 weeks.
Common misunderstanding
A "significant" secondary outcome does not rescue a study whose primary outcome was not clearly different. With many secondary outcomes, some will appear significant by chance, so they should be interpreted as supportive or exploratory unless the study was designed and powered for them.
Learn more
See How to Write Research Objectives.
References and further reading
- Chan AW, Tetzlaff JM, Altman DG, et al. SPIRIT 2013 statement: defining standard protocol items for clinical trials. Ann Intern Med. 2013;158(3):200-207. doi:10.7326/0003-4819-158-3-201301080-00007
- Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010;340:c332. doi:10.1136/bmj.c332
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.