To estimate this endogenized trend, a model anal- ogous to the error correction representation above was supplemented by an endogenous trend term, including determinants such as non-fossil fuel sup- ply, manufacturing component of GDP, trade, and investment. Price is also included as high prices may stimulate innovation. In addition there is a stochas- tic trend, which is taken to represent the autono- mous improvement in technology. The model was estimated using the Kalman filter, as described by Cuthbertson et al [7]) expressed as Equations (3a)-(3c):