The PEFR of a group of 11yr old girls follow a normal distribution with mean 300 l/min and standard deviation 20 l/min. Which of the following statements is true in this regard:
1.About 95% of girls have PEFR between 260 and 340 1/min
2.The girls have healthy lungs
3.About 5% of girls have PEFR below 260 1/min
4.All the PEFR must be less than 340 1/min
sol:
a. Area between one standard deviation on either side of the mean (x + 1 ü-) will include approximately 68% in the distribution.
b. The area between two SD on either side of the mean (x + 2 ü) approximately 95 %.
c. Area between three SD on either side of mean (x + 3 ü) approximately 99.7 % in the distribution.
d. The probability of a reading falling outside the 95% confidence limits is 20 (p=0.05.)