**Core Concept**
Repetition of a study in a given group refers to the re-examination of a sample or population to confirm or refute previous findings. This concept is crucial in clinical research, as it helps to establish the reliability and validity of study results.

**Why the Correct Answer is Right**
The repetition of a study in a given group is essential to account for various sources of bias and error that may have occurred during the initial study. This includes measurement error, sampling bias, and the influence of external factors on the study population. By re-examining the same group, researchers can increase the confidence in their results and identify potential flaws in the initial study. Additionally, repetition of a study can help to establish the long-term effects of a treatment or intervention.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because repetition of a study in a given group is not the same as a **pilot study**, which is a preliminary study conducted to assess the feasibility of a larger study.
* **Option B:** This option is incorrect because **meta-analysis** involves combining the results of multiple studies to draw a more general conclusion, rather than re-examining the same group.
* **Option C:** This option is incorrect because **crossover study** design involves having each participant receive different treatments at different times, rather than re-examining the same group.

**Clinical Pearl / High-Yield Fact**
When designing a study, it's essential to consider the potential sources of bias and error that may affect the results. Repetition of a study in a given group can help to mitigate these issues and increase the reliability of the findings.

**Correct Answer: C. Crossover study