A researcher wants to evaluate the effect of a new diet regimen on weight of a group of 10 patients. He records their weight before & after the regimen. Which of following statistical test will be applicable in this case?

**Core Concept**
The underlying principle being tested is the appropriate statistical analysis for comparing paired data, specifically weights before and after a diet regimen. This involves understanding the concept of **paired samples** and the statistical tests applicable to such data.

**Why the Correct Answer is Right**
The correct answer is applicable because it is a statistical test used for comparing two related samples, which is the case here where each patient's weight is measured before and after the regimen. This test evaluates the **null hypothesis** that the difference between the paired observations is zero, using the **t-distribution**.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not specified, but typically, other options like ANOVA or regression might be incorrect as they are used for different types of data or comparisons.
**Option B:** Similarly, without the specific option, we can say that if it involves unpaired data or a different type of comparison, it would be incorrect.
**Option C:** If this option involves a non-parametric test or a test for unpaired data, it would not be appropriate for paired samples.
**Option D:** If not the correct paired test, then this option is also incorrect.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that when comparing paired data, such as before and after measurements in the same subjects, a **paired t-test** is the appropriate statistical analysis if the data are normally distributed.

**Correct Answer:** Correct Answer: D. Paired t-test.

✓ Correct Answer: B. Paired t - test