Inter Quartile Range (IQR) – also called the midspread or middle 50% or technically H-spread is a measure of statistical dispersion being equal to the difference between 75th and 25th percentiles or between upper and lower quartiles IQR = Q3 − Q1. In other words the IQR is the first quartile subtracted from the third quartile these quartiles can be clearly seen on a box plot on the data it is a trimmed estimator defined as the 25% trimmed range and is the most significant basic robust measure of scale
