Median and Quartiles

Median and Quartiles

1. Median

   • The number that is exactly halfway between the highest and lowest numbers in a sequence.
   • Method 1
     • 1. You MUST write the terms in order before you do anything else.
       • 2. Count the terms
         • 3. Work out which term the median will be. (eg if there are 16 terms, you add 1 to the 16 and then divide by 2 = 8.5, so it will be halfway between the 8th and 9th terms)
           • FORMULA: (n+1)/2 = the number term you need
   • Method 2
     • 1. You MUST put the terms in order first.
       • Cross them off from either side until you get to the middle. If you are left with 2, add them together and half the answer.

2. Quartiles

   • Upper
     • The number at 3/4 of the way through a sequence.
     • Do the same as for the lower quartile, but instead of doing the number of terms over 4, do 3/4 times the number of terms.
     • NOTE: You can just find the median of the upper half of the sequence
     • EASIEST METHOD
       • Find the term at this place
         • 3(n+1)/4
   • Lower
     • The number at 1/4 of the way through a sequence
     • Find which term it will be.
       • (number of terms)/4
         • eg if there are 16 terms, it will be the 4th term
       • Go to that term in the sequence, and if it is a whole number, add 0.5 to it. This is the lower quartile.
     • NOTE: You can just find the median of the lower half of the data.
     • EASIEST METHOD
       • find the term at this place
         • (n+1)/4
   • Interquartile Range
     • UQ - LQ = IQR