In case of \\[\epsilon_i \sim \mathit{N}(0,\sigma^2)\\] $$ \frac{\hat \beta_j - \beta_j}{\mathit se(\hat \beta_j)} \sim \mathit t_{n-k} $$ $$ \frac{\mathit RSS}{\sigma^2} \sim \chi^2_{n-k} $$ $$ \frac{(\mathit RSS_R - RSS_{UR})/r}{RSS_{UR}/(\mathit n-k_{UR})} \sim \mathit F_{r,n-k_{UR}} $$