**Core Concept**
The correct answer tests the understanding of paired data analysis in statistical inference. Paired data refers to measurements or observations made on the same subjects before and after a treatment or exposure to a factor. This type of data requires specialized statistical techniques to account for the correlation between the paired measurements.

**Why the Correct Answer is Right**
The paired T-test is a statistical test used to compare the means of two related groups of samples. It is specifically designed for paired data, where each subject serves as its own control. This test assumes that the differences between the paired measurements are normally distributed and have equal variances. By comparing the means of the paired measurements before and after the exposure, the paired T-test can detect significant changes or effects of the factor on the subjects. The paired T-test is a powerful tool for evaluating the efficacy of interventions, treatments, or exposures in a controlled setting.

**Why Each Wrong Option is Incorrect**
**Option A:** The Chi-square test is a non-parametric test used for categorical data, not paired continuous data. It is not suitable for analyzing the differences in means between paired measurements.

**Option B:** The Unpaired T-test is used to compare the means of two independent groups of samples. It is not designed for paired data, where each subject serves as its own control.

**Option D:** This option is a repeat of the correct answer, C. Paired T-test.

**Clinical Pearl / High-Yield Fact**
When designing a study to evaluate the effects of a factor on a population, researchers should consider using paired data analysis techniques, such as the paired T-test, to maximize the statistical power and reduce the risk of type II errors.

**Correct Answer:**
✓ Correct Answer: C. Paired T-test