At the first level of measurement, numbers are used to classify
data. In fact words or letters would be equally appropriate.
Say you wanted to classify a football team into left footed
and right footed players, you could put all the left footed
players into a group classified as 1 and all the right footed
ones into a group classified as 2. The numbers 1 and 2 are
used for convenience, you could equally use the letters L
and R, or the words LEFT and RIGHT to label the groups of
players.
Numbers are often preferred because text takes longer to type
out and takes up more space. Another example is blood groups
where the letter A, B, O and AB represent the different classes
