Scales of Measurement* |
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Name |
Measurement Principles |
Appropriate Arithmetic Operations |
Example |
| Ratio | A zero scale value truly indicates that a zero amount of the attribute is present. Equal ratios of change in scale values produce equal changes in the amount of the attribute measured. (Double the scale value produces double the amount of the attribute.) |
Operations that treat distance from zero as meaningful (multiplication and division). | Height, Weight |
| Interval | Interval size across adjacent scale values represent a constant increment in the attribute measured. The values attached to the beginning or end of a scale are arbitrarily assigned. Double the scale value does not mean double the amount of the attribute. |
Operations that treat distances along scale as meaningful (addition and subtraction). | Fahrenheit, Centigrade scales; IQ, SAT |
| Ordinal | Observations with a higher scale value have more of some attribute. The interval size across scale values is inconsistent or indeterminate. Scale assignment corresponds to "greater than," "equal to," or "less than." |
Any operation that preserves rank order of cases. | Level of "liking" |
| Nominal | Observations fall into mutually exclusive categories. People or objects in a category are equivalent on some attribute. Numeric values assigned to a category are best treated as labels. |
Counting cases. | Marital Status |
*Based on a typology by S. S. Stevens (1946, 1951) |
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