How accurate are GDP calculations? Off by a few billion dollars?

Question

there are several methods to measure GDP for a country... but when economists actually collect the data -- how much error is in the numbers? I never see a "standard deviation" or confidence limit for GDP figures... why is that?

Answer 1

Real growth rate are frequently revised , sometimes as much as 1/2 of a percent so the error must be on that order. However the absolute value of GDP is probably not that good because of the difficulty in measuring  many  badly reported sectors. I have seen estimates that  the government  misses as much  as 10 to 20% of the economic activity.