Confidence votes 100. Like the standard deviation, the interquartile range (IQR) is a descriptive statistic used to summarize the extent of the spread of your data. The IQR is the distance between the 1st quartile (25th percentile) and 3rd quartile (75th percentile). Q3 - Q1 = IQR. To find these numbers you must divide your data set in half, and find the median of each half and that will be your Q1 and Q3.