Why do your GDP (Gross Domestic Product) statistics differ from other sources?
We have two sets of GDP dollar estimates in The World Factbook , one derived from purchasing power parity (PPP) calculations and the other derived from official exchange rates (OER). Other sources probably use one of the two. See the Definitions and Notes section on GDP and GDP methodology for more information.
On the CIA Web site, Chiefs of State is updated weekly, but the last update for the Factbook was an earlier date. Why the discrepancy?
Although Chiefs of State and The World Factbook both appear on the CIA Web site, they are produced and updated by separate staffs. Chiefs of State includes fewer countries but more leaders, and is updated more frequently than The World Factbook, which has a much larger database, and includes all countries.
Some percentage distributions do not add to 100. Why not?
Because of rounding, percentage distributions do not always add precisely to 100%. Rounding of numbers always results in a loss of precision - i.e., error. This error becomes apparent when percentage data are totaled, as the following two examples show:
Original Data Rounded to whole integer
Example 1 43.2 43
30.4 30
26.4 26
—— —
100.0 99
Example 2 42.8 43
31.6 32
25.6 26
—— —
100.0 101
When this occurs, we do not force the numbers to add exactly to 100, because doing so would introduce additional error into the distribution.