Input-output analysis is often extended in two ways. First, by including data on factor payments, sources of household income, and the pattern of household goods consumption across various social groups (such as urban and rural households), a social accounting matrix (SAM) is created. This is accomplished by adding data from the system of national accounts, balance of payments, and flow-of-funds databases, often supplemented with household survey data, to the basic input-output table. A SAM therefore provides a comprehensive and detailed quantitative description of the interrelationships in an economy as they exist at a point in time, making it well suited as a tool for evaluating the impact of alternative development policies. SAMs for many countries can be found online. SAMs are often further elaborated with computable general equilibrium (CGE) models, which assume that households maximize utility and firms maximize profits. Utility (or demand) and production functions are assumed or estimated from national data. The resulting impact of the policy is then simulated using standard computer programs. The CGE approach is more complicated than a SAM, but its value lies in enabling policymakers to take into account the possible reactions of consumers and firms to the alternative policies being considered rather than assume that they will behave the way they did before the new policies were implemented