What is often included in a ratio scale that distinguishes it from other scales?

A ratio scale is distinguished from other types of measurement scales by the presence of a true zero point. This means that a ratio scale allows for the expression of meaningful quantities that can be measured in absolute terms. In practical terms, having a true zero means that a value of zero on this scale indicates the complete absence of the quantity being measured. For instance, in measuring weight, a zero value indicates no weight at all, which allows for the calculation of ratios between values (e.g., 10 kg is twice as heavy as 5 kg).

In contrast, ordinal scales involve ranking without precise measurement of the differences between rankings, nominal scales categorize data without any inherent order, and interval scales have measurement units but do not have a true zero point (e.g., temperature in Celsius or Fahrenheit, where zero does not mean the absence of temperature). Therefore, the existence of a true zero point is what qualifies a scale as a ratio scale, enabling a more complete and informative analysis of the data.