What is it? Why is it important?
Variables are medical values or information of interest to a researcher. During study conduct only variables defined in the study protocol can be collected.
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 variable 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?
- Define variables needed to answer your study question including
- 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 with respect to the 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
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 visit 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
Basel, Clinical Trials Unit, CTU, dkf.unibas.ch
Bellinzona, 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.ctc.usz.ch
ICH GCP E6(R2) – see in particular guideline
- 5.5. Trial Management, data handling, and record-keeping
ClinO – see in particular article and annex
- Art. 5 Rules of Good Clinical Practice
- Annex 3 Application documents to be submitted to EC