Development↦Statistic Methodology↦Statistics in the Protocol↦Primary and Secondary Analysis
What is it? Why is it important?
The terms "primary analysis" and "secondary analysis" refer to different levels of importance with respect to the study aim.
The aim of a primary analysis is to address the primary research question of the study (i.e. the main question for which the study was designed, and for which the study is expected to provide an answer).
The primary analysis generally involves the analysis of the primary and potentially secondary (i.e. of secondary interest) study outcomes/endpoints.
The aim of a secondary analyses is to investigate aspects beyond the primary research question. Secondary analyses may include the analysis of:
- Additional (e.g. exploratory) outcomes/endpoints
- Subgroups, with the aim to examine the outcome(s) in study population subgroups (e.g. young patients, women)
- Study efficacy (i.e. assessing the performance of an intervention among participants who did closely follow the study protocol)
Secondary analyses, contribute to a more comprehensive understanding of study results.
What do I need to do?
As a SP-INV, define in your study protocol the planned primary and, if applicable, secondary analyses.
Discuss your analysis plans with a statistician. Include both primary- and secondary analyses in the study protocol and, if applicable, in the Statistical Analysis Plan (SAP).
Note: a research question can define several outcomes (e.g. mortality rate, safety, disease reoccurrence). Still, one outcome is considered more important than the others, and consequently defined as the primary outcome/endpoint. The others are still of interest to the research question but remain secondary.
Where can I get help?
Your local CTU↧ can support you with experienced staff regarding this topic
Basel, Departement Klinische Forschung, CTU, dkf.unibas.ch
Lugano, Clinical Trials Unit, CTU-EOC, www.ctueoc.ch
Bern, Clinical Trials Unit, CTU, www.ctu.unibe.ch
Geneva, Clinical Research Center, CRC, crc.hug.ch
Lausanne, Clinical Research Center, CRC, www.chuv.ch
St. Gallen, Clinical Trials Unit, CTU, www.kssg.ch
Zürich, Clinical Trials Center, CTC, www.usz.ch
References
ICH Topic E9 – see in particular
- 2.2.4 Multiple primary variables
- 5.1 Prespecification of the analysis