Definition Interval scale

The interval scale is a type of metric scale and reflects quantitative values. In terms of levels of measurement, the interval scale is located above the nominal and ordinal scales.

In interval scales, the location parameters mode, median, and mean can be calculated. An interval scale can always be divided into equal portion scales, e.g., rulers can be used to measure length, and stopwatches can be used to measure time intervals.

Another typical example is the Celsius scale, which is divided into 100 equal degree sections between the freezing and boiling points of water. Unlike the intervals in nominal and ordinal scales, it is possible to make calculations with individual data points in interval scales. The difference in temperature between 10°C and 20°C is the same distance as between 40°C and 50°C. In contrast to ratio scales, interval scales lack a natural zero point. In the case of the Celsius temperature scale, '0°C' is an arbitrarily chosen zero point (whereas the Kelvin temperature scale begins at the absolute zero point with 0K (-273.15°C/-459.67°F). Multiplications with an interval scale are therefore not useful. While it is true for the Kelvin ratio scale that 100K defines double the heat energy in a mass as 50K, this is not true for 50°C/100°C.

Another type of interval scale is a rating scale. With rating scales, it is usually assumed that the distances between the single expressions of evaluation (score) are equal. However, there is no natural zero point. Thus, it is possible to calculate an average of a rating scale, but it is not possible to make the statement that the score 8 (on a scale of 1 to 11) is twice as high as the score 4.