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A principal investigator (PI) is the lead scientist for a particular well-defined science (or other...

A principal investigator (PI) is the lead scientist for a particular well-defined science (or other academic) project, such as an astronomical observing campaign, laboratory study or clinical trial. In the context of federal funding from agencies such as NASA or the NSF, the PI is the person who takes direct responsibility for completion of a funded project, directing the research and reporting directly to the funding agency. For small projects (which might involve 1-5 people) the PI is typically the person who conceived of the investigation, but for larger projects (such as the construction of scientific spacecraft or observatories) the PI may be selected by a team to obtain the best strategic advantage for the project. In the context of a clinical trial a PI may be an academic working with grants from NIH or other funding agencies, or may be effectively a contractor for a pharmaceutical company working on testing the safety and efficacy of new medicines.