Quartiles for even and odd length data set in data mining
What is quartile?
Quartile means four equal groups.
How to find quartiles of odd length data set?
Example:
Data = 8, 5, 2, 4, 8, 9, 5 
Step 1:
First of all, arrange the values in order.
After ordering the values:
Data = 2, 4, 5, 5, 8, 8, 9 
Step 2:
For dividing this data into four equal parts, we needed three quartiles.
Q1: Lower quartile
Q2: Median of the data set
Q3: Upper quartile
Step 3:
Find the median of the data set and label it as Q2.
Data = 2, 4, 5, 5, 8, 8, 9
Q1: 4 – Lower quartile Q2: 5 – Middle quartile Q3: 8 – Upper quartile Inter Quartile Range= Q3 – Q1 = 8 – 4 = 4 What is Outlier? The outlier is the set of data far away from the common and famous pattern. How to find outliers?Outlier is mostly a value higher or lower than 1.5 * IQR =1.5 * IQR =1.5 * 5 = 7.5 Population size: Population size is the total number of values in data. 
How to find quartiles of even length data set?
Example:
Data = 8, 5, 2, 4, 8, 9, 5,7 
Step 1:
First of all, arrange the values in order
After ordering the values:
Data = 2, 4, 5, 5, 7, 8, 8, 9 
Step 2:
For dividing this data into four equal parts, we needed three quartiles.
Q1: Lower quartile
Q2: Median of the data set
Q3: Upper quartile
Step 3:
Find the median of the data set and label it as Q2.
Data = 2, 4, ♦ 5, 5, ♦ 7, 8 ♦ 8, 9
Minimum: 2 Q1: 4 + 5 / 2 = 4.5 Lower quartile Q2: 5+ 7 / 2 = 6 Middle quartile Q3: 8 + 8 / 2 = 8 Upper quartile Maximum: 9 Inter Quartile Range= Q3 – Q1 = 8 – 4.5 = 3.5 Outlier is mostly a value higher or lower than 1.5 * IQR =1.5 * IQR =1.5 * 3.5 = 5.25 
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