Scale of Measurement

The process of measurement involves assigning numbers to observations according to rules. The way that the numbers are assigned determines the scale of measurement. Four scales of measurement are typically discussed in psychological statistics -- nominal, ordinal, interval and ratio. We will add a fifth scale of measurement -- approximately interval. Each scale of measurement represents a particular property or set of properties of the abstract number system. The mathematical properties of the numbers you are going to analyze are important because they determine which statistics you can use.

Properties of the Abstract Number System

The properties of the abstract number system that are relevant to scale of measurement are identity, magnitude, equal interval, and absolute/true zero.

Identity means that each number has a particular meaning.

Magnitude means that numbers have an inherent order from smaller to larger.

Equal intervals means that the differences between numbers (units) anywhere on the scale is the same (e.g., the difference between 4 and 5 is the same as the difference between 76 and 77).

Absolute/true zero means that the zero point represents the absence of the property being measured (e.g., no money, no behavior, none correct).

Now let's try some examples. Select either examples of levels of measurement you may encounter in everyday life or those typically found in psychological research.

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	*Identity* means that each number has a particular meaning.
	*Magnitude* means that numbers have an inherent order from smaller to larger.
	*Equal intervals* means that the differences between numbers (units) anywhere on the scale is the same (e.g., the difference between 4 and 5 is the same as the difference between 76 and 77).
	Absolute/true zero means that the zero point represents the absence of the property being measured (e.g., no money, no behavior, none correct).