# What are Scales of Measurement?

Introduction

Scales of measurement or levels of measurement were developed by American psychologist Stanley Smith Stevens(November 4, 1906 – January 18, 1973).

He classified variables into four levels: nominal, ordinal, interval, and ratio.

Based on the order of four levels, the usable operators get more and more from nominal to ratio.

Four Scales of Measurement

(1) Nominal scale:

Nominal scales are applied to distinguish objects or abstract definitions.

Therefore, there are only equal or unequal meaning between variables.

Operators: ＝, ≠.

Example: mode, name, blood types, gender, etc.

(2) Ordinal scale:

Ordinal scales are used to rank objects but the distances between each other are not meaningful.

Operators: ＝, ≠, >, <.

Example: median, rank, preference, etc.

(3) Interval scale:

Interval scales can be used to rank objects and the distances between each other are meaningful.

However, the ratios are not meaningful.

Operators: ＝, ≠, >, <, +, -.

Example: mean, Celsius temperature, IQ, etc.

(4) Ratio scale:

Ratio scales possess all the properties of interval scales and meaningful absolute zero.

Therefore, the ratios are meaningful in ratio scales.

Operators: ＝, ≠, >, <, +, -, ×, ÷.

Example: absolute temperature, length, weight, volume, etc.

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