Glossary
Principal investigator (PI)
The person responsible for a study's scientific and technical direction and, at a site, for its conduct, staff and participants, even when tasks are delegated.
What does Principal investigator (PI) mean in clinical research?
ClinicalTrials.gov regulations define the principal investigator as the individual responsible for the overall scientific and technical direction of the study.[1] At a site, the PI signs the regulatory commitments, supervises the study team, and is accountable for how participants are recruited, consented and treated. ICH E6(R3) lets the investigator delegate trial-related activities to other persons or parties while keeping responsibility for them.[2]
PIs shape enrollment directly: their clinic, referral network and time for the study all affect how quickly a site enrolls, and sponsors weigh PI experience when choosing sites. In the CREST-2 trial, the PI's specialty was among the factors associated with faster recruitment in univariate analysis.[3]
Practical note: delegation covers technology too. When a vendor tool reviews charts or contacts patients, the PI still owns those steps, so the delegation log, IRB approvals and vendor oversight should reflect them. Identify keeps an audit trail of screening decisions and the evidence behind them for that review.
Sources
- 1.42 CFR 11.10 Definitions (Clinical Trials Registration and Results Information Submission) · eCFR (NIH/NLM), 2026
- 2.ICH E6(R3) Guideline for Good Clinical Practice · International Council for Harmonisation (ICH), 2025
- 3.Factors Associated With Time to Site Activation, Randomization, and Enrollment Performance in a Stroke Prevention Trial · Stroke (American Heart Association), via PubMed, 2017Quote: "By univariate analysis, factors associated with faster recruitment were authorization to randomize in both trials, principal investigator specialties of interventional radiology and cardiology, pre-trial reported performance >50 carotid angioplasty and stenting procedures per year, status in the top half of recruitment in the CREST trial, and classification as a private health facility."