19. In the simple linear regression model Y = ,60 +lx+6, the quantity 8 is a random variable, assumed to be normally distributed with E( ) = 0, and We ) = 0' . The estimated standard error of f}, (the least squares estimated of ,3, ), denoted by 535' , is divided by , where s = .JSSE [(n 2) and Sn = X(x,. .1_:)2