To find the interquartile range (IQR), follow these steps:

1. Order the data from least to greatest.
2. Find the median of the entire data set. This splits the data into two halves.
3. Find the lower quartile (Q1) , which is the median of the lower half of the data (the 25th percentile).
4. Find the upper quartile (Q3) , which is the median of the upper half of the data (the 75th percentile).
5. Calculate the interquartile range by subtracting the lower quartile from the upper quartile:

IQR=Q3−Q1\text{IQR}=Q3-Q1IQR=Q3−Q1

The IQR represents the range of the middle 50% of the data, showing the spread of the central portion of the dataset

. For example, if Q1 is 3 and Q3 is 12, then the IQR is 12−3=912-3=912−3=9

. This method helps to measure variability while reducing the effect of outliers compared to the full range