Ranks are determined by sorting the data into order and replacing each value by its relative position in the order. For example, suppose the original data consists of the values:

1.9 2.7 2.1 3.1 2.5

In sorted order, the values are:

1.9 2.1 2.5 2.7 3.1

These values are replaced by their relative positions:

1 2 3 4 5

The largest value is given a rank of 5 and the smallest value is given a rank of 1. This results in larger ranks being associated with larger values and smaller ranks being associated with smaller values. This makes the interpretation of the plots simpler. The end result is the following ranked data set:

1 4 2 5 3

This is the data actually analyzed when the analysis is based on ranked data.