What is a Ratio Scale? Definition and Example

In most social science studies, various characteristics or behaviors of respondents are determined and compared with each other in order to place them later in a larger social context. To measure these characteristics, the response options in a survey must be quantified so that they can then be statistically evaluated. If researchers need exact numbers for their study, for example regarding the body height of respondents, they use the ratio scale.

General Definition of the Ratio Scale

A ratio scale (ratio scale) is the highest metric scale level, used to make complex statements about relationships between different variables or measurement units. This scale includes measurements with characteristics such as length, body height, weight, speed, but also the frequency of previous hospital stays, the number of children or the weekly amount of consumed alcohol.

Ratio-scaled characteristics not only have equally large distances as an interval scale, but also have a natural or absolute zero point.

By natural zero point is meant the physiological property of characteristics such as body weight: By nature, there is no person who weighs less than 0 grams. On the interval scale, the zero point is also present, but it is determined by humans and can be exceeded (= minus degrees in Celsius temperature). In contrast to this arbitrary zero point of interval-scaled data, the natural zero point of the ratio scale cannot be exceeded (= no negative number in body weight possible).

For a characteristic like weight, it is therefore easy to make such statements that variable A (100 kilograms) and variable B (150 kilograms) together result in the weight of variable C (250 kilograms). For interval-scaled data such as Celsius temperature, this is again not possible: A temperature of -5°C and a daily temperature of +10°C cannot be added to arrive at +5°C – that simply makes no sense.

 

 

Typical Use of the Ratio Scale

In research, a ratio scale is most frequently used for physiological measurements (e.g., reaction speed of respondents) because it enables extremely precise measurement. In the social sciences, ratio-scaled data can be collected through a survey (e.g., questions about body weight in a nutrition study) or from observations (e.g., frequency and duration of mobile phone use on the train). Also, in empirical studies, data on concrete amounts of money (e.g., gross salary of test persons) are collected on a ratio scale.

Example: How much money do you spend on food per month? Please round your answer down.

• 100 euros or less
• 150 euros
• 200 euros
• 250 euros
• 300 euros
• 350 euros
• 400 euros
• 450 euros
• 500 euros or more

 

Ratio-scaled data thus allow the application of all arithmetic operations and can also be used to calculate all statistical values, including mode, median, quantiles, mean, variance, standard deviation and geometric mean. Nevertheless, the use of a ratio scale in the social sciences is relatively rare because the data from an interval scale is completely sufficient for most studies.