**Question:** One standard deviation in normal standard curve includes value-

A. 0.68
B. 0.95
C. 0.99
D. 0.997

**Core Concept:**
The concept being tested in this question is related to the concept of standard deviations in statistics and their relationship to probability. In a normal distribution curve, most of the data points are usually found within one, two, or three standard deviations from the mean.

**Why the Correct Answer is Right:**
The correct answer, D. 0.997, represents the probability that a randomly selected value from a normal distribution will fall within one standard deviation of the mean. In other words, one standard deviation encompasses approximately 68% of the values in a normal distribution.

**Why Each Wrong Option is Incorrect:**
A. 0.68 (Option A) is incorrect because it represents the probability that a value falls within one standard deviation of the mean.
B. 0.95 (Option B) is incorrect because it represents the probability that a value falls within two standard deviations of the mean.
C. 0.99 (Option C) is incorrect because it represents the probability that a value falls within one standard deviation of the mean, not two standard deviations.

**Why the Correct Answer is Right:**

**Clinical Pearl:**
The concept of standard deviations and their relationship to probability is essential in understanding statistical data analysis and interpretation in medical research, clinical trials, and medical decision making.

**Correct Answer:** 0.997 (Option D) represents the probability that a value falls within one standard deviation of the mean. This is important in clinical practice as it helps to understand the likelihood of a patient's value falling within a specific range of the normal distribution, which can be useful in interpreting laboratory test results and making clinical decisions based on statistical data.