To find the IQR, find the median or center of the data, calculate the median of the lower and upper halves of the data, and find the difference between the medians of the lower and upper halves of data. You need a data set, a calculator, and pencil and paper to complete this task.
- Put the data in order
To find the median of the whole set, order the data from least to greatest.
- Find the median or center
For an odd set of data, the median is the number that has an equal amount of numbers on both sides of it. If the data set is even, find the center of the data where there is an equal amount of numbers greater and lesser than that point.
- Find the median or center of the upper and lower halves
For an odd set of data, disregard the median. Instead, look at the halves below it and above it, and find the medians of them. For an even set of data, find the medians of both halves below and above the center of the data.
- Subtract the upper-half median by the lower-half median
Take the median of the upper half that you found, and subtract it from the median of the lower half to find the IQR.