I am not sure what method use for computation a lower and upper quartil. In my textbook there is a rule for lower quartil -"lower quartil is median of lower half of data" and "upper quartil is median of upper half of data". But when I compute these quartils in Open Office Calc the results are different.
For example I have this table of frequencies:
value frequency
3 1
6 4
7 15
8 10
10 10
In my oppinion (and according to my textbook) the upper quartile is 9 and not 7,5 as is counted in OpenOffice Calc.
What value is correct?