Expert: Sherry Wallin - 12/25/2010

Question
While calculating Quartile deviation for indiviual observation we
use the formula
Q1=value of {(n+1)/4}th observation
Q3=value of {3(n+1)/4}th observation
and then  Q.D = Q3-Q1/2
Why do we use n+1 in the formula (please explain)
Because
while calculating Q.D for group frequency distributuion
we use n/4 where in both of these n is the total number of
observation  

[Difficulty]
why do we use n+1 in the formula for Q.D for individual observation


[Thoughts]
While calculating Quartile deviation for indiviual observation we
use the formula
Q1=value of {(n+1)/4}th observation
Q3=value of {3(n+1)/4}th observation
and then  Q.D = Q3-Q1/2
Why do we use n+1 in the formula (please explain)
Because
while calculating Q.D for group frequency distributuion
we use n/4 where in both of these n is the total number of observation

Answer
Dhananjay~

If you want to know how many days are left in say December and today is the 24th, how do you count them? I always take one more number than the 31 in December and subtract off the 24, i.e., 32-24 = 8 days. Now let's count them one by one instead, 24,25,26,27,28,29,30,31 and you see indeed that there are 8 days left in December counting today. Notice 32 is n+1 = 31 + 1

Math Prof