What is it? Why is it important?

An Interim Analysis (IA) is done before all data collection is complete, so as to evaluate the safetyProtocol and efficacy of the study while the study is still ongoing.

An IA is recommended when:

  • A treatment is expected to be particularly beneficial or harmful compared to placebo
  • Based on ethical considerations, treatment differences must be assessed in order to decide early on whether to continue, adapt or terminate the study
  • A study is planned to last for many years


An IA must be planned prior to study implementation or be approved through an amendment. Timing and rational of IAs must be defined in the study protocol.

What do I need to do?

Perform the IA as defined by the study protocol, which might include:

  • The timing of IA (e.g. after the inclusion of x amounts of participants, after visit x)
  • Statistical methods used
  • Guidelines for the interpretation of results (e.g. upper- lower tolerability defining study continuation, adaptations, or study stop)
  • The decision whether to continue, adapt, or terminate the study
  • If requested by EC/RA submit an applicable IA report

For more information refer to Statistics in this Study Guide.


If the study must be terminated, follow protocol procedures and initiate study closure.

Where can I get help?

Your local CTU can support you with experienced staff regarding this topic


ICH GCP E6(R2) – see in particular guidelines

  • 5.4.1 Interim report
  • 6.9.1 Statistics, interim analysis
  • CTU – Clinical Trials Unit
  • EC/RA – Ethics Committee / Regulatory Authorities
  • IA – Interim Analysis
  • ICH-GCP – International Council for Harmonisation - Good Clinical Practice
Conduct ↦ Management ↦ Safety ↦ Interim Analysis

Provides some background knowledge and basic definitions

Basic Protocol
Basic Statistics
Basic Monitoring
Basic Drug or Device
Basic Biobanking

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Protocol
Concept Statistics
Concept Drug or Device
Concept Biobanking

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Protocol
Development Statistics
Development Drug or Device
Development Biobanking

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Protocol
Set-Up Ethics and Laws
Set-Up Statistics
Set-Up Quality and Risk
Set-Up Drug or Device
Set-Up Biobanking

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Protocol
Conduct Statistics
Conduct Drug or Device
Conduct Biobanking

Starts with last study visit completed

Ends after study publication and archiving

Completion Protocol
Completion Statistics
Completion Drug or Device
Completion Biobanking
Current Path (click to copy): Conduct ↦ Management ↦ Safety ↦ Interim Analysis

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