Introduction

The following is Wikipedia's definition of machine learning:

"Machine learning is a scientific discipline that explores the construction and study of algorithms that can learn from data."

Essentially, machine learning is making use of past data to make predictions about the future. Machine learning heavily depends upon statistical analysis and methodology.

In statistics, there are four types of measurement scales:

Scale type	Description
Nominal Scale	=, ≠ Identifies categories Can't be numeric Example: male, female
Ordinal Scale	=, ≠, <, > Nominal scale + Ranks from least important to most important Example: corporate hierarchy
Interval Scale	=, ≠, <, >, +, - Ordinal scale + distance between observations Numbers assigned to observations indicate order Difference between any consecutive values is same as others 60° temperature is not the double of 30°
Ratio Scale	=, ≠, <, >, +, ×, ÷ ...