What Does It Mean to Control for a Variable in Regression?

An intuitive explanation

While interpreting the coefficient of one of the predictors (say a continuous variable X1) of an empirical model — with multiple explanatory variables (X1, X2, …..Xn) predicting the value of an outcome variable (Y) — you must have used these statements: “controlling for other factors/holding other factors constant/accounting for other factors/keeping other factors fixed, one unit increase in X1 is, on average, associated with b units …

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