2. QUARTILES
• It is a type of quantile (cutpoints).
• These are the values that divide
a list of numbers into quarters.
• Each set of scores has three
quartiles.
3. • A quartile divides a sorted data set into 4
equal parts, so that each part represents
¼ of the data set.
4. –The FIRST QUARTILE (Q1) also
called lower quartile is defined as
the middle number between the
smallest number and the median of
the data set. (25th percentile)
–The SECOND QUARTILE (Q2) is
the median of the data. (50th
percentile)
–The THIRD QUARTILE (Q3) also
called the upper quartile is the
middle value between the median
and the highest value of the data
set. (75th percentile)
5. EXAMPLE
• 3; 4; 5; 6; 6; 7; 8; 9; 9; 10; 11
There are 11 data items
The median is the 5th item. So M = 7
The lower quartile is the 3rd item. So Q1 = 5
The upper quartile is the 9th item. So Q3 = 9
6. (3; 4; 5; 6; 6; 7; 8; 9; 9; 10; 11)
• ¼ or 25% of the data has a value that is
less than or equal to 5.
• ½ or 50% of the data has a value that is
less than or equal to 7
• ¾ or 75% of the data has a value that is
less than or equal to 9
• ½ or 50% of the data lies between 5 and 9
