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Practical Predictive Analytics by Ralph Winters

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Nominal data

Nominal data, sometimes referred to as categorical data, simply defines a class or group without any natural order. Nominal variables are usually character data, but not always. Your gender, the cell phone brand you prefer, and the type of book you are reading now are all examples of nominal variables. Sometimes it can be tricky, since the number 1 and 2 written on a sign are also nominal variables when they are used to designate two possible waiting lines you may need to visit at the motor vehicle bureau. Nominal data only designates classes and you cannot perform any mathematical operations on them, such as addition or subtraction.

When characterizing nominal data, the only measure of central tendency is the mode, which is ...

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