**Question:** In case of normal curve, the limits mean +/- 2SD cover:

**Core Concept:** A normal curve, also known as a Gaussian distribution, is a statistical concept that describes the distribution of data points around the mean. The standard deviation (SD) is a measure of the spread of data points from the mean. In the context of a normal curve, two standard deviations (2SD) represent a range that is expected to encompass 95% of the data points.

**Why the Correct Answer is Right:** The normal curve is symmetrical, and the mean, median, and mode are the same. The standard deviation defines the width of the curve, with a smaller SD indicating a more concentrated distribution. Two standard deviations (2SD) from the mean are used to define the range that includes 95% of the data points.

**Why Each Wrong Option is Incorrect:**

A. This option incorrectly refers to "+/- 1SD," which would cover only 68% of the data points, as 1SD represents the range that includes approximately 68% of the data points.
B. This option is incorrect because it refers to "+/- 3SD," which would cover only 99.7% of the data points, as 3SD represents the range that includes approximately 99.7% of the data points.
C. This option is incorrect, as it refers to "+/- 4SD," which would cover only 99.97% of the data points, as 4SD represents the range that includes approximately 99.97% of the data points.
D. This option is incorrect because it refers to "+/- 5SD," which would cover only 99.9997% of the data points, as 5SD represents the range that includes approximately 99.9997% of the data points.

**Clinical Pearl:** In clinical practice, understanding the concept of a normal distribution and the relationship between the mean, median, mode, and standard deviation is essential for interpreting and making decisions based on test results, such as blood pressure, body mass index (BMI), or other markers of health and disease.

**Correct Answer:** A. +/- 1SD

**Explanation:** A normal distribution with a mean of 0 and a standard deviation of 1 (SD) results in a range of +/-1SD covering approximately 68% of the data points. This is the most commonly used normal distribution in clinical practice, representing the range that includes 68% of the data points, which is considered the standard deviation or "one standard deviation" from the mean.