Social Research Glossary A B C D E F G H I J K L M N O P Q R S T U V W X Y Z Home
Citation reference: Harvey, L., 2012-24, Social Research Glossary, Quality Research International, http://www.qualityresearchinternational.com/socialresearch/
This is a dynamic glossary and the author would welcome any e-mail suggestions for additions or amendments.
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Measurement scales
Measurement scales or levels of measurement refers to the nature of enumerated data.
Introduction
Measurement might simply be effected by grouping items into categories, by ranking items in order, or by giving items a score that indicates an order of magnitude on a given scale. The common classification of levels of measurement are into nominal, ordinal, interval and ratio scales.
A nominal scale is a system of categorisation and the simplest form of measurement. The categories are a set of convenient, mutually exclusive and exhaustive labels. It is not implied that they should be in any particular order or preference. A set of political party options in an opinion poll constitute a set of nominal categories (e.g., Labour, Conservative, SDP, Liberal, Others).
A nominal variable is one which may be placed on a nominal scale only. It is sometimes known as an attribute.
A nominal scale can be treated as an interval scale for some data analysis applications when it is a dichotomy (e.g. gender).
Ordinal scales are where items are ranked in order but there is no consistent and identifiable interval between rank scores (even if they are designated by a contiguous scale of numbers) (E.g. preference rated 1 to 5 for 'very good', 'good', 'indifferent', 'bad, 'very bad'.)
An interval scale is a measurement scale in which the items on a scale are ranked in order and the intervals between the scale points are equal (in real terms) but which has no true zero point.
In an interval scale a score of say 15 is as far above 10 as 20 is above 15, but 20 need not represent twice as much of the quantity being measured as 10 does.
Both the Fahrenheit and Celsius scales of temperature are interval scales.
The scales of many psychological tests and I.Q tests are constructed as though they were interval scales, however, the extent to which the points on the scale are truly equal intervals is debateable.
An interval variable is a variable that may be measured on an interval scale.
For most purposes, ratio scales can be treated as interval scales.
A ratio scale is an interval scale with a fixed and meaningful zero. (E.g. time, temperature measured in degrees absolute).
The diagram below shows which statistical tests are appropriate for different measurement scales.
See also
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