According to Tony Gardner-Medwin, the certainty based score (CBS) is expressed by the equation,
CBS = ( (T-E)/(3N-E) )^p × 100%, where p = 0.4*(1+E/N) , E=expected no. correct by chance, T=Total of CBM marks (max 3N), and N=no. of Questions seen. Does anyone know how to calculate E? having trouble figuring it out.