From this CBO paper:
SOURCE: Congressional Budget Office.
NOTES: This figure shows the estimated likelihood of alternative projections of the surplus or deficit under current policies. The calculations are based on CBO's past track record. CBO's January 2002 baseline projections fall in the middle of the darkest area. Under the assumption that policies do not change, the probability is 10 percent that actual surpluses or deficits will fall in the darkest area and 90 percent that they will fall within the whole shaded area.
Actual surpluses or deficits will of course be affected by legislation enacted during the next 10 years, including decisions about discretionary spending. The effects of future legislation are not included in this figure.
An explanation of how this probability distribution was calculated is available at www.cbo.gov.
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