One of the first things you learn in introductory statistics is about levels of measurement. Statisticians identify four such levels, nominal, ordinal, interval and ratio, each of which in turn provides more precise information.

Nominal variables are categories with no implicit order. Sex, race and alive/dead are examples. Ordinal measures add ordering to the categories. An illustration is a customer satisfaction measure that ranges from very dissatisfied to very satisfied, represented by levels 1 to 5. Another illustration is education, with “Not a HS grad”, “HS grad”, “Some college” and “College grad” as levels. If the distances between each level along the scale can be interpreted as equal, the measure is called interval. Examples of interval variables are temperature, IQ and aptitude test scores. Finally, if an interval variable has a real zero point, it is then identified as ratio. Heart rate, revenue, profit, customer value and churn percentage are examples.

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