According to economists, this episode of great recession was resulted from a sudden busting of house bubble in US, where the house bubble was caused by rapid growth of improper regulation on sub-prime mortgages (Merriam 2009; Wang 2009; Whitney 2007).
When working with equations that have two variables, the coordinate plane is an important tool. It's a way to draw pictures of equations that makes them easier to understand. To create a coordinate plane, start with a sheet of graph or grid paper. Next, draw a horizontal line.
continuous, you'd be assuming each of the steps had the same magnitude. categorical and you'd have the same model as if you included the Z1, Z2, and Z3 variables. cases you would have used 3 df (4-1=3 for the Z variable and 1+1+1=3 for the 3 Z1, Z2, Z3 variables).