**Core Concept**
Good Clinical Practice (GCP) is an international ethical and scientific quality standard for the design, conduct, recording, and reporting of trials that involve the participation of human subjects. GCP ensures that trials are conducted with the highest ethical and methodological standards to protect the rights, safety, and well-being of trial participants.

**Why the Correct Answer is Right**
GCP is primarily applicable to clinical trials, which are prospective, systematic studies designed to evaluate the safety and efficacy of a new medical intervention. GCP is not required for observational studies, research on existing data, or non-interventional studies where the investigator does not have control over the intervention. In such cases, Good Research Practice (GRP) or Good Observational Studies Practice (GOSP) may be more relevant.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because observational studies, although not requiring GCP, may still be subject to GCP principles if they involve the use of medical devices or interventions that are not part of standard care.

**Option B:** This option is incorrect because research on existing data, such as database analysis, may still require adherence to GCP principles if the analysis involves the use of patient data in a way that could compromise their confidentiality or privacy.

**Option C:** This option is incorrect because non-interventional studies, although not requiring GCP, may still be subject to GCP principles if they involve the use of medical devices or interventions that are not part of standard care.

**Clinical Pearl / High-Yield Fact**
It is essential to note that even if GCP is not required, researchers must still adhere to the principles of Good Research Practice (GRP) to ensure the integrity and validity of their research.

**Correct Answer: C.