Detection and Replacement of Outliers using Interquartile Range(IQR)

Outlier

• An observation which differs from an overall pattern on a sample dataset is called an outlier.

Interquartile Range

• The IQR method divides a data set into quartiles to measure variability.
• The information is arranged in ascending order and divided into four equal parts.(Q1, Q2, Q3, Q4)
• A dataset has 2n / 2n+1 data points, then (n > 2)
  • Q1 : median of the dataset.
  • Q2 : median of n smallest data points.
  • Q3 : median of n highest data points.
• IQR is the range between the first and the third quartiles namely Q1 and Q3 (IQR = Q3 - Q1)
• The outliers are data points which fall below Q1 – 1.5*IQR or above Q3 + 1.5*IQR.