**Core Concept:** A normal curve or Gaussian distribution is a type of continuous probability distribution that describes a data set where nearly all values fall within one or two standard deviations of the mean. Normal curves are often used in medical statistics to understand the distribution of clinical data.

**Why the Correct Answer is Right:** The correct answer, C, represents 68% of the values in a normally distributed data set. This is because in a normal curve, approximately 68% of the data falls within one standard deviation of the mean.

**Why Each Wrong Option is Incorrect:**
A. 62% (incorrect because it is slightly less than 68%)
B. 72% (incorrect because it is greater than 68%)
D. 50% (incorrect because it represents the area within the mean, not one standard deviation)

**Clinical Pearl / High-Yield Fact:** Remember that in a normal distribution, approximately 68% of values fall within one standard deviation from the mean. This is an important concept in medical statistics and helps doctors understand the distribution of clinical data.

**Correct Answer:** C. 68%