Published on July 16, 2020 by Pritha Bhandari. Revised on December 3, 2021. Levels of measurement, also called scales of measurement, tell you how precisely
variables are recorded. In scientific research, a variable is anything that can take on different values across your data set (e.g., height or test scores). There are 4 levels of measurement: Depending on the level of measurement of the variable, what you can do to analyze your data may be limited. There is a hierarchy in the complexity and precision of the level of measurement, from low (nominal) to high (ratio). Going from lowest to highest, the 4 levels of measurement are cumulative. This means that they each take on the properties of lower levels and add new properties. Although you can rank the top 5 Olympic medallists, this scale does not tell you how close or far apart they are in number of wins. The difference between any two adjacent temperatures is the same: one degree. But zero degrees is defined differently depending on the scale – it doesn’t mean an absolute absence of temperature. The same is true for test scores and
personality inventories. A zero on a test is arbitrary; it does not mean that the test-taker has an absolute lack of the trait being measured. A true zero means there is an absence of the variable of interest. In ratio scales, zero does mean an absolute lack of the variable. For example, in the Kelvin temperature scale, there are no negative degrees of temperature – zero means an
absolute lack of thermal energy. The level at which you measure a variable determines how you can analyze your data. The different levels limit which descriptive statistics you can use to get an overall summary of your data, and which type of
inferential statistics you can perform on your data to support or refute your hypothesis. In many cases, your variables can be measured at different levels, so you have to choose the level of measurement you will use before data collection begins. At a ratio level, you can see that the difference between A and B’s incomes is far greater than the difference between B and C’s incomes. At an ordinal level, however, you only know the income bracket for each participant, not their exact income. Since you cannot say exactly how much each income differs from the others in your data set, you can only order the income levels and group the participants. Professional editors proofread and edit your paper by focusing on:Nominal, ordinal,
interval, and ratio data
Nominal levelExamples of nominal scales You can categorize your data by labelling them in mutually exclusive groups, but there is no order between the categories.
Ordinal levelExamples of ordinal scales You can categorize and rank your data in an order, but you cannot say anything about the intervals between the rankings. Interval levelExamples of interval scales You can categorize, rank, and infer equal intervals between neighboring data points, but there is no true zero point. Ratio levelExamples of ratio scales You can categorize, rank, and infer equal intervals between neighboring data points, and there is a true zero point. Why are levels of measurement important?
ParticipantIncome (ordinal level)Income (ratio level) A Bracket 1
$12,550
B Bracket 2
$39,700
C Bracket 3
$40,300
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Which descriptive statistics can I apply on my data?
Descriptive statistics help you get an idea of the “middle” and “spread” of your data through measures of central tendency and variability.
When measuring the central tendency or variability of your data set, your level of measurement decides which methods you can use based on the mathematical operations that are appropriate for each level.
The methods you can apply are cumulative; at higher levels, you can apply all mathematical operations and measures used at lower levels.
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Quiz: Nominal, ordinal, interval, or ratio?
Frequently asked questions about levels of measurement
How do I decide which level of measurement to use?
Some variables have fixed levels. For example, gender and ethnicity are always nominal level data because they cannot be ranked.
However, for other variables, you can choose the level of measurement. For example, income is a variable that can be recorded on an ordinal or a ratio scale:
- At an ordinal level, you could create 5 income groupings and code the incomes that fall within them from 1–5.
- At a ratio level, you would record exact numbers for income.
If you have a choice, the ratio level is always preferable because you can analyze data in more ways. The higher the level of measurement, the more precise your data is.
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