Both. They occur for any of the following reasons:

• to verify data that has been submitted to the agency
• if any complaints have been submitted in regard to that particular investigational site
• if any sponsors have concerns
• upon termination of the clinical site
• to provide real-time assessment of the investigator’s conduct of the trial and protection of human subjects during an ongoing trial
• at the request of an FDA review division
• for trials that are being conducted on investigational products that have been identified as a product of special interest

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