You should not include more than one categorical variable in a multiple regression because the use of two or more will cause misleading results.

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Multiple regression models can include multiple categorical variables. These variables are typically encoded using techniques such as one-hot encoding to transform them into a format that can be used in the regression analysis. Including multiple categorical variables allows for the analysis of their individual and interaction effects on the dependent variable, provided the model is correctly specified and multicollinearity is addressed.

You Should Not Include More Than One Categorical Variable in a Multiple