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A data set contains information on a number of cases. Cases may be customers, companies, subjects in a study, units in an experiment, or other objects.

For each case, the data give values for one or more variables. A variable describes some characteristic of a case, such as a person’s height, gender, or salary. Variables can have different values for different cases.

A label is a special variable used to identify cases in a data set. Some variables are categorical and others are quantitative. A categorical variable places each individual into a category, such as male or female. A quantitative variable has numerical values that measure some characteristicof each case, such as height in centimeters or annual salary in dollars.

The key characteristics of a data set answer the questions Who?, What?, and Why?