What is it? Why is it important?

Variables are medical values or information of interest to a researcher. When planning and setting-up a study, only variables defined in the study protocol can be collected and used for analysis.

Variables are either:

  • Quantitative based on the process of counting or measuring something (e.g. age, weight, lab values, health scores, percentage)
  • Qualitative which are non-numerical characteristics but can be fitted according to categories (e.g. eye colour, gender, education)

Research variables are often discussed in terms of cause and effect relationships (e.g. cigarette smoking can cause lung cancer).


Here some varaible guidelines to follow:

  • Variables should provide all necessary information to a researcher needed to answer the study question
  • Variables entered in the study database (eCRF) should be collected as completely as possible. Incomplete or missing variables should be avoided
  • The visit-plan defining the schedule of study visit during study conduct must be followed. No visits must be removed or added as this would alter the amount of variables being collected
  • Submit the CRF (eCRF and pCRF) with its list of variables to the EC for approval
  • In the event a researcher wants to collect additional data not defined in the study protocol, he/she must initially submit a protocol amendment to the EC for approval. The same would apply to changes to the study visit-plan. Only after EC approval can changes be implemented

What do I need to do?

As a SP-INV:

  • Define variables needed to answer your study question including
    • The source (SD) where the data is retrieved (e.g. laboratory reports, physical examination, medical history, patient file,  participant diary)
    • Means used to collect data (e.g. iPad/tablet, pCRF, questionnaires, physician interviews)
  • Consult a statistician to ensure variables are suitable for statistical analysis, such as:
    • The selection of appropriate and measurable study variables. This is especially important in order to ensure variables are useful in the interpretation of study results (e.g. study endpoint)
    • The implementation of harmonised data formats (e.g. implemented codes, classifications)
  • Document selected variables and their rationale in the study protocol and the DMP


For more information refer to Statistics and Protocol in this Trial Guide.


During study conduct the collection of variables might depend on study progress, such as:

  • Some study endpoint variables are only collected towards the end of a study (e.g. cancer status 6 months after treatment stop, % blood pressure improvement after 6 weeks treatment compared to baseline)
  • Descriptive variables might only be collected at the beginning of the study, such as during a screening- or baseline visit (e.g. age, gender, disease characteristics at study start, level of education, socioeconomic factors)

The visit-plan provides a good overview to study staff and ensures that no variables are forgotten during study conduct. Thus, the collection of study variables should be well structured:

  • List study visits in chronological order based on study progress (e.g. screening visit, baseline visit, followed by interim- until last study visit)
  • Group those variables together that are repeatedly collected during subsequent visits (e.g. recurrent medical examinations)
  • Group variables according to the time point when they must be collected

Where can I get help?

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


ICH GCP E6(R2) – see in particular guideline

  • 5.5. Trial Management, data handling, and record-keeping

Swiss Law

ClinO – see in particular article and annex

  • Art. 5 Rules of Good Clinical Practice
  • Annex 3 Application documents to be submitted to EC
  • ClinO – Clinical Trials Ordinance
  • CTU – Clinical Trials Unit
  • DMP – Data Management Plan
  • EC – Ethics Committee
  • CRF – Case Report Form
  • eCRF – electronic Case Report Form
  • pCRF – paper Case Report Form
  • ICH GCP – International Council for Harmonisation Good Clinical Practice
  • SD – Source Data
  • SP-INV – Sponsor-Investigator
Development ↦ Data Handling ↦ Database Development ↦ Variables

Provides some background knowledge and basic definitions

Basic Protocol
Basic Statistics
Basic Monitoring
Basic Drug or Device

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Protocol
Concept Statistics
Concept Drug or Device

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Protocol
Development Statistics
Development Drug or Device

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

Starts with participant recruitment

Ends after the last participant has completed the last study visit

Conduct Protocol
Conduct Statistics
Conduct Drug or Device

Starts with last study visit completed

Ends after study publication and archiving

Completion Protocol
Completion Statistics
Completion Drug or Device
Current Path (click to copy): Development ↦ Data Handling ↦ Database Development ↦ Variables

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