# HELP...S1 Question!Watch

#1
Will somebody please clear things up for me as Im really confused. When finding medians and quartiles; under what circumstances do we use M=(n+1)/2 th observation and when do we only use M=(n/2)th observation. So wil somebody tell we what to use for stem and leafs, grouped frequencies etc. I also have in my notes something about for discrete data if (n/4) is and integer r use 0.5(r + r+1), if between integers r and r+1 use r+1.

Can anybody explain how I know which to use!?
Thanks.
0
12 years ago
#2
For the M=(n/2)th observation, you only use it when interpolating for grouped data.

You use (n + 1)/2 for a discrete frequency data.
0
12 years ago
#3
its different for the quantiles and the median
when trying to find the median you use the formula 1/2(n+1) to give you the observation as in if you get 6 you go to the 6th number but if it is 6.5 you use the 6th and 7th number
wheras with quantiles if you get 6.5 for the equation 1/2(n) then you round up 6.5 to 7 and use the 7th number
hope that helps.....
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