Directional Random Effect Model and Its Covariance Structure

The Directional Random Effect Model (DREM) is defined. The model is developed from random effect Rasch model. When the link function is a polynomial or an exponential function, the covariance structure of DREM is given out. When the link function is a general form, an approximate covariance structure of DREM is given out. These covariance structures and approximate covariance structure have the similiar form as the covariance structure of the linear random effect model.