Measurement is the assignment of values to outcomes following a set of rules—simple. The results are the different scales we’ll define in a moment, and an outcome is anything we are interested in measuring, such as hair color, gender, test score, or height. These scales of measurement, or rules, are the particular levels at which outcomes are observed. Each level has a particular set of characteristics, and scales of measurement come in four flavors (there are four types): nominal, ordinal, interval, and ratio.
