What is an interval scale? Definition and example

Every empirical study requires a uniform standard with which different characteristics of the examined object can be captured. In a quantitative survey, an appropriate scale is created to obtain systematic measured values or data from response options. In social research, psychological and social properties of examined persons are largely measured on an interval scale.

General Definition of the Interval Scale

The interval scale (Latin "intervallum" = space, distance, gap) is a metric or numerical scale in which individual units have a direct numerical value. With the interval scale, both the classification of examination objects (as with the nominal scale) and the ordering of examined elements (as with the ordinal scale) can be performed.

Additionally, an interval scale also measures the exact difference between individual elements. This is because the distance between any two consecutive objects on an interval scale must be equal. In a survey, the intervals between the 1st and 2nd response option are therefore the same as between the 4th and 5th.

Measurement of temperature in Celsius belongs to this scale because exactly one degree lies between the sections of the thermometer. However, unlike a ratio scale, the interval scale has no natural zero point, that is, no physical lower limit. This means that the temperature display in Celsius can also fall below zero and thus negative values are possible.

With the interval scale, it can be stated that between -10 and +5 degrees Celsius the same distance lies as between +15 and +30 degrees Celsius. However, the ratio between the two characteristics cannot be shown because the same distance (15 degrees in both cases) without a natural zero point certainly does not mean that both distances can be interpreted as equally warm.

 

 

Typical Use of the Interval Scale

In research practice, the interval scale plays a crucial role. With the help of the interval scale, opinions, preferences, motives and character traits of the examined persons are captured, among other things, in market research. To measure interval-scaled data, respondents complete various self-disclosures, where they usually rate their behaviors step-by-step on rating scales.

Example 1: I find the current political situation worrying.

• Strongly agree
• Mostly agree
• Somewhat agree
• Mostly disagree
• Strongly disagree

 

Example 2: Please rate the taste of this lemonade on a scale from 0 (not tasty) to 10 (exceptionally tasty).

• 0
• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10

 

Interval-scaled data can be meaningfully evaluated with the most frequently used statistical procedures. With interval-scaled data, various differences, sums and means are thus easily calculated. The interval scale is a good choice for many empirical studies.