Levels Of Measurement - what you can and can't do arithmetically
Knowing the level of measurement you are dealing with is
important because it helps you to decide what arithmetic and
statistical operations you can carry out on the values that
have been assigned.
A spreadsheet package like Excel will allow you to perform
all sorts of complex calculations on tables of data
but the results you get may be meaningless if you dont
understand which operations are permissible for each level.
For instance, you can assign 1 to males and 2 to females,
but if you add up all the values, the total will not help