Levels of Measurement

     Variables may have different levels of measurement ranging from nominal to ordinal to interval and, lastly, ratio. An easy way to remember these levels are by the acronym NOIR. S.S. Stevens (1946) identified these 4 labels of measurement.

Nominal Measures (lowest/simplest form of measurement)
     Nominal measures are measures with names or labels for characteristics such as gender, race, city of residence, college major, social security number, and marital status. Numerical assignment for these measurements are arbitrary, for example, if we are measuring race, 1 could stand for White, 2 could stand for White, 3 for Asian, and so on.
Remember: NAME

Ordinal Measures
     Ordinal measures are meausres whose attributes may be logically rank-ordered. For example, level of education is an ordinal measure. Someone with a graduate degree would mean more of an education than a high school graduate. Fear of crime is another example of an ordinal measure. In other words, numbers assigned here are not arbitrary. Numbers here indicate a ranking order. For example, if we are measuring "fear of crime" and posing the question "I feel my neighborhood is safe." and 1 = strongly disagree, 2= somewhat disagree, 3= neutral, 4=somewhat agree, 5=strongly agree, then these are different levels. It is important to note this is not an intrinsic scale, meaning you only know relative differences between the responses. You cannot measure the differences.
Remember: ORDERED

Interval Measures
     An example of an interval measure is temperature. Interval measures have distances between the attributes that have meaning. In the example above the distance between education is arbitrary, but the distance between temperature has meaning. Here, numbers have rankings and also have values. An example of an interval measure is temperature.
Remember: KNOWN INTERVAL/DIFFERENCE

Ratio Measures (highest level of measurement)
 Ratio measures have all of the characteristics in the lower levels of measurement but also have a true zero point. An example of a ratio measure includes income and coming from a criminal justice perspective can also include number of prior arrests as well as length of incarceration. Weight is also an example of a ratio measure.
Remember: TRUE ZERO

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Levels of Measurement

Great Video Explanations:
https://www.youtube.com/watch?v=LPHYPXBK_ks
http://youtu.be/hZxnzfnt5v8