Intercept and linear regression

Question

What happens to the intercept if you add variables to the regression model (increase, decrease, remain the same) and why?

Answer 1

The intercept is the predicted  value when all the  predictors are equal to 0. So adding new predictors can cause the intercept to increase or decrease, by pretty much any amount, based on the mean of the  predictor you're adding and the size/direction of its corresponding regression coefficient.