Categorical variables are those variables having two or more groups or levels such as sex, ethnicity, and religious group.
They may be called independent variables even though they are not true independent variables under experimental control.
Categorical variables, also called grouping variables, can be created from continuous variables. For example, researchers often obtain the age of their study participants. Age is a continuous variable but sometimes, researchers group ages together and compare how people of different age groups answer questions on a survey.
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