Dummy variable

PrepNuggets

LEVEL II

In multiple linear regression, a dummy variable is a binary variable that is used to represent a categorical independent variable. These variables take on the value of 1 or 0, indicating the presence or absence of a particular category. For example, suppose we want to test whether stock returns were different in January than during the remaining months of a particular year, which is a type of market anomaly called the “January effect”,  we include an independent variable that takes on value “1” if it is a January, and “0” if it is any other month of the year. 

When using multiple dummy variables in a regression model, it is important to use one less dummy variable than the total number of categories.

Compare: Logistic regression