The exact value within +-2 SD in Standard normal curve
**Core Concept**
The standard normal curve, also known as the **z-distribution** or **Gaussian distribution**, is a probability distribution that is symmetric about the mean, showing that data near the mean are more frequent in occurrence than data far from the mean. In a standard normal curve, the mean is 0 and the standard deviation is 1.
**Why the Correct Answer is Right**
About 95% of the area under the standard normal curve lies within 2 standard deviations of the mean. This corresponds to approximately 95% of the data points falling within 2 standard deviations of the mean in a normal distribution.
**Why Each Wrong Option is Incorrect**
**Option A:** This option does not accurately represent the percentage of data points within 2 standard deviations of the mean.
**Option B:** This option is also incorrect as it does not accurately describe the area under the curve within 2 standard deviations.
**Option D:** Similarly, this option does not accurately represent the data points within 2 standard deviations.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that about 68% of the data falls within 1 standard deviation of the mean, about 95% of the data falls within 2 standard deviations, and about 99.7% of the data falls within 3 standard deviations in a **normal distribution**.
**Correct Answer:** C. 95%