Ratio Scale:

A ratio scale is a measurement scale in which a certain distance along the scale means the same thing no matter where on the scale you are, and where "0" on the scale represents the absence of the thing being measured. Thus a "4" on such a scale implies twice as much of the thing being measured as a "2."

See also: nominal scale, ordinal scale, interval scale

This topic is covered in the following online courses at statistics.com:

• Introductory Statistics
• Understanding Standardized Testing