In the Scheidel–Friesen economic model, the total annual income generated by the Empire is placed at nearly 20 billion "sestertii", with about 5 percent extracted by central and local government. Households in the top 1.5 percent of income distribution captured about 20 percent of income. Another 20 percent went to about 10 percent of the population who can be characterized as a non-elite middle. The remaining "vast majority" produced more than half of the total income, but lived near subsistence. All cited economic historians stress the point that any estimate can only be regarded as a rough approximation to the realities of the ancient economy, given the general paucity of surviving pertinent data.