Independence of observations, bivariate normality, homoscedasticity (in the population, the variances in the dependent variable are equal for all values of the independent variable) HELPFUL FOR:

What value of Y would you expect to be related to any value of X? There is no basis for predicting other than the mean of Y. This line would be horizontal intersecting Y at the mean. *The regression line improves the prediction of Y based on any value of X. a Regression line fits data better than a horizontal line. It is better than using the mean of Y as a predicted result of all values of X