Although 40° is twice as many degrees as 20°, it isn’t twice as hot on the Celsius or Fahrenheit scales. That means that you can only calculate ratios of temperatures in the Kelvin scale. However, unlike the Celsius and Fahrenheit scales where zero is just another temperature value, the Kelvin scale has a true zero (0 K) where nothing can be colder. In all 3 scales, there are equal intervals between neighboring points. While Celsius and Fahrenheit are interval scales, Kelvin is a ratio scale. Some variables, such as temperature, can be measured on different scales. Similarly, 8 years is double 4 years of experience. For example, you can say that 4 children is twice as many as 2 children in a household. With a true zero in your scale, you can calculate ratios of values. For example, the number of children in a household or years of work experience are ratio variables: A respondent can have no children in their household or zero years of work experience. On a ratio scale, a zero means there’s a total absence of the variable of interest. Many more statistical tests can be performed on quantitative than categorical data.

While nominal and ordinal variables are categorical variables, interval and ratio variables are quantitative variables. At the ratio level, values can be categorized, ordered, have equal intervals and take on a true zero. The ratio level contains all of the features of the other 3 levels. The higher the level, the more complex the measurement is. The levels, or scales, of measurement indicate how precisely data is recorded. The ratio level is the highest of four hierarchical levels of measurement. Frequently asked questions about ratio data.

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