What is it? Why is it important?

The research question must be clear and answerable. A good way to build a research question is to use the PICO model.


PICO stands for:

  • P – Population: describes the study population and its characteristics (e.g. age, gender, geographic location, health problem, diagnosis)
  • I – Intervention: describes the treatment or exposure being studied. In the health care system, this could include the:
    • Administration of a drug treatment
    • Conduct of a diagnostic test (e.g. testing a new tool to measure blood pressure)
    • Any other type of procedure (e.g. recommendation regarding life style changes)
  • C – Comparison: describes a potential alternative or reference point to the intervention (e.g. a control or comparison group such as a placebo group)
  • O – Outcome: describes the parameter(s) that will be measured to address the objective of the study (e.g. to assess the success of an intervention)


Example: A study with anaemic women and the objective of assessing the effect of iron intake on haemoglobin status.


  • Population: adult women (age between 18 and 60) with anaemia living in Switzerland
  • Intervention: daily intake of an iron tablet (e.g. iron dose = 320mg / tablet, ingested orally for 3 months)
  • Comparison: daily intake of a placebo tablet (iron dose = 0 mg / tablet, ingested orally for 3 months)
  • Outcome:  change in haemoglobin values between study start (baseline) and study end (after 3 months of intervention)

What do I need to do?

As a SP-INV, describe your research question based on the PICO model.


Consult a statistician to ensure the research question is statistically:

  • Answerable: the study outcome includes parameters that are measurable and that can be analysed statistically (e.g. blood parameters, various health scores such as pain scores or quality of life scores)
  • Clear: complying with the PICO model will ensure that the research question becomes clear, as it contains all the required information for the set-up and planning of the study.


In some studies the aim is not to quantify the effect of an intervention (I) on an outcome (O). The aim is rather to describe a given population (e.g. frequency of patients with a cardiac event in the cancer department of a hospital). Thus, there is no actual intervention and no comparison is made to a control group. In these types of studies, I and C questions of the PICO model are not applicable. The research question is only built using the P and O questions (e.g. P: patients of the cancer department, O: occurrence of cardiac event during hospital stay).

Where can I get help?

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

  • CTU – Clinical Trials Unit
  • SP-INV – Sponsor Investigator
  • PICO – Population, Intervention, Comparison, Outcome
Basic ↦ Statistics ↦ Research Question ↦ Definition

Provides some background knowledge and basic definitions

Basic Monitoring
Basic Drug or Device

Starts with a study idea

Ends after having assessed and evaluated study feasibility

Concept Drug or Device

Starts with confidence that the study is feasible

Ends after having received ethics and regulatory approval

Development Drug or Device

Starts with ethics and regulatory approval

Ends after successful study initiation

Set-Up Ethics and Laws
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 Drug or Device

Starts with last study visit completed

Ends after study publication and archiving

Completion Statistics
Completion Drug or Device
Current Path (click to copy): Basic ↦ Statistics ↦ Research Question ↦ Definition

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