Year-end level from annual financial statements compiled by and purchased from SNL Financial. Staff tabulation of U.S. government agency securities from Schedule D, book value. Levels for other quarters estimated from staff tabulation of quarterly statement, table Assets, percentage of line 1, Bonds. Percentage used is FOF Section estimate based on distribution of annual bond data. Unadjusted flow is the change in the level; data for the most recent ten years show no significant seasonality.