The modelling work used as an assumption that current policies would continue. On this basis, it assumed that rents would increase at RPI + 0.5 per cent. following convergence with formula rents in 2011-12 and that allowances would rise in line with GDP. Interest charges were based on local consolidated rate of interest forecasts. The modelling work however also tested sensitivity to changes in all the variables which have an impact on a business plan, including debt levels, interest and inflation rates, expenditure levels, rental and other income, and sales. The 30-year model business plans run well beyond medium term forecasts and policy commitments so it is important to consider a wide range of scenarios.