A theory of electron thermal diffusivity has been proposed which is based on electron drift wave turbulence. When account is taken of the effect of local shear changes produced in high poloidal beta equilibrium, this theory is found to predict the observed improvement of tokamak confinement with plasma current. Confinement is good at low poloidal beta, degrades as poloidal beta increases and then enters an improved transport region at high poloidal beta.