The PEFR of a group of 11 year old girls follow a normal distribution with mean 300 1/min and standard deviation 201/min
**Core Concept**
The question is testing the understanding of a normal distribution and how to calculate the percentage of individuals within a certain range of values, specifically in relation to **peak expiratory flow rate (PEFR)**. The **mean** and **standard deviation** are given, which are crucial for determining the distribution of values.
**Why the Correct Answer is Right**
Given that the PEFR follows a **normal distribution**, about 68% of the values fall within one standard deviation of the mean, about 95% fall within two standard deviations, and about 99.7% fall within three standard deviations. This is based on the **68-95-99.7 rule**.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not correctly apply the principles of a normal distribution.
**Option B:** Similarly, this option does not align with the expected distribution of values based on the given mean and standard deviation.
**Option D:** This option is also incorrect as it misinterprets how the standard deviation relates to the distribution of PEFR values.
**Clinical Pearl / High-Yield Fact**
In clinical practice, understanding the distribution of physiological parameters like PEFR is crucial for diagnosing and managing respiratory conditions. Remember, about 95% of values in a normal distribution lie within two standard deviations of the mean.
**Correct Answer:** D. 99.7% of girls will have a PEFR between -102 and 702 1/min