(1) Independent	$y_{\mathit{\text{it}}}^{\ast }={\mathbf{\text{x}}}_{\mathit{\text{it}}}\mathit{\beta }+u_{\mathit{\text{it}}}$
(2) State dependence	$y_{\mathit{\text{it}}}^{\ast }={\mathbf{\text{x}}}_{\mathit{\text{it}}}\mathit{\beta }+y_{i,t-1}\gamma +u_{\mathit{\text{it}}}$
(3) Random effects (RE)	$y_{\mathit{\text{it}}}^{\ast }={\mathbf{\text{x}}}_{\mathit{\text{it}}}\mathit{\beta }+a_i+u_{\mathit{\text{it}}}$
(4) State dependence and RE	$y_{\mathit{\text{it}}}^{\ast }={\mathbf{\text{x}}}_{\mathit{\text{it}}}\mathit{\beta }+y_{i,t-1}\gamma +a_i+u_{\mathit{\text{it}}}$