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

References

ICH Topic E9 – see in particular

  • 2.2.4 Multiple primary variables
  • 5.1 Prespecification of the analysis
Abbreviations
  • CTU – Clinical Trials Unit
  • ICH – International Council for Harmonisation
  • SAP – Statistical Analysis Plan
  • SP-INV – Sponsor Investigator
Development ↦ Statistic Methodology ↦ Statistics in the Protocol ↦ Primary and Secondary Analysis
Study
Basic

Provides some background knowledge and basic definitions

Basic Monitoring
Basic Drug or Device
Concept

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Statistic Methodology
Concept Drug or Device
Development

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Drug or Device
Set-Up

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Ethics and Laws
Set-Up Statistic Methodology
Set-Up Quality and Risk
Set-Up Drug or Device
Conduct

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Statistic Methodology
Conduct Drug or Device
Completion

Starts with last study visit completed

Ends after study publication and archiving

Completion Statistic Methodology
Completion Drug or Device
Current Path (click to copy): Development ↦ Statistic Methodology ↦ Statistics in the Protocol ↦ Primary and Secondary Analysis

Please note: the Easy-GCS tool is currently under construction.