# Introduction

We classify data obtained from measurements using numbers and we can do this with different levels of precision or levels of measurement.

There are 4 levels of measurement and it is important to know what level of measurement you are working with as this partly determines the arithmetic and statistical operations you can carry out on them.

The four levels of measurement in ascending order of precision are: nominal, ordinal, interval and ratio.

As we go on to describe and give examples of each of these levels you'll see that the numbers used to describe nominal data are simply used to classify data whereas the numbers describing interval or ratio measurements are much more precise and represent actual amounts.