  # Ordinal Number

## What is an Ordinal Number?

Much like the name implies, an ordinal number is a number used to express the order of an item, or set of items. An ordinal number is different than a cardinal number, which is used rather to describe the amount of items in total, rather than their specific order. A natural number is one that can fit under both categories, ordinal and cardinal. For example, the number 0 is a natural number as it can both describe the size of a set, as well as the position of an element in a list.

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## Ordinal Numbers and Machine Learning

Ordinal numbers are used in machine learning, particularly when scientists want to perform ordinal regressions. An ordinal regression is a regression that is used in predicting a variable in which the order, or sequence, of variables is significant. For example, social scientists often gather data that is defined by scales of human preferences (i.e. feelings of positivity 1-5). In order to predict certain variables about a population with that data, the scientists often turn to ordinal regression. In machine learning, this process is sometimes also known as ranked learning.