## **Core Concept**
The question tests understanding of the normal distribution curve, also known as the Gaussian distribution or bell curve, which is a fundamental concept in statistics and biostatistics. The normal distribution curve is symmetric about its mean, and the area under the curve represents the total probability of all possible outcomes. The standard deviation (SD) is a measure of the amount of variation or dispersion of a set of values.

## **Why the Correct Answer is Right**
In a normal distribution curve, about 68% of the area under the curve lies within one standard deviation of the mean. This is a well-established statistical fact. The mean (μ) is the central tendency, and the standard deviation (σ) measures the dispersion or variability. The area between one standard deviation on either side of the mean (μ - σ to μ + σ) encompasses approximately 68.2% of the total area under the curve. This corresponds to option B, 68.2%.

## **Why Each Wrong Option is Incorrect**
- **Option A:** 95% refers to the area under the curve within two standard deviations of the mean, not one.
- **Option C:** 99.7% refers to the area under the curve within three standard deviations of the mean, also known as the empirical rule or the 68-95-99.7 rule.
- **Option D:** 100% would represent the entire area under the curve, which is not specific to one standard deviation on either side of the mean.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is the 68-95-99.7 rule, which states that in a normal distribution, about 68% of the data falls within one standard deviation of the mean, about 95% falls within two standard deviations, and about 99.7% falls within three standard deviations. This rule is crucial for understanding and interpreting data in medical research and practice.

## **Correct Answer:** B. 68.2%