What are the four levels of measurement? What distinguishes one level of measurement from another?

There are four (4) levels of measurement

1. Nominal-level scales - exhibit no particular order among the groupings or categories. The categories are mutually exclusive. For example, the variable "gender" has a nominal scale, because there is no ordering, and one is either male or female.
2. Ordinal-level scales - exhibit order/hierarchy among the categories, but distance is indeterminable. For example, "anger" can be measured in terms of: irritated, aggravated, and raging mad. Although "raging mad" is angrier than "aggravated," we cannot say how much more.
3. Interval-level scales - exhibit order and determinable distance, (usually constant) but do not have a true zero (0) value. For example, IQ - An IQ of 0 is not defined
4. Ratio-level scales - exhibit order among the categories, have determinable distance, and have a meaningful or true zero (0) value. For example, an income of $40,000 is twice as much as an income of $20,000, and people can have an income of $0.

Distinctions between ratio and interval-level variables are typically not relevant in public and nonprofit management. Variables with ordinal or nominal-level scales are called categorical/discrete variables while variables with interval or ratio-level scales are called continuous variables.

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