As educated citizens, there is no single measure of economy that we care more about than the GDP figure. Any increase or decrease in the change of GDP growth rate are bound to make national headlines. Witness the news media frenzy following the GDP figure release for China:

Clearly, as a society, we regard the GDP figure as something more than a number that measures how large the economy is or the rate at which it is expanding (or contracting); but rather, we see GDP as almost a sacred figure. We take pride in our national economic output, we base our consumer confidence based on these numbers, and more importantly, politicians and decision-makers based their course of actions upon the changes in these numbers from year-to-year. We take the number as something that’s grounded in reality and something that’s unquestionable. And while some would argue about the usefulness of the GDP figure as a measure of the standard of living, most would accept the accuracy of those numbers. But how accurate is it really of a nation’s economic output? Here are several surprising facts that shows that perhaps GDP is not all that it seems. (For a similar list about inflation, click here)

1. Ghana GDP revision: In 2010, Ghana decided to reexamine its GDP figures by using a different base year to calculate growth over time. The result? GDP was revised upward by over 60%.

2. Nigerian GDP revision: In 2014 Nigeria recalculated its GDP (using a different base year) to include more sectors of the economy such as telecommunications. This recalculation resulted in Nigeria shifting its economic output by upwards of 80% and leading it to become the largest economy on the African continent, surpassing South Africa.

3. Japan’s GDP calculation mistake: For the 4th quarter of 2012, Japan’s GDP was calculated as shrinking by 0.3%. In reality it increased 0.1%. This miscalculation was the result of a failure to correct seasonally-adjusted figures and misreporting of the GDP deflator (a measure of inflation).

4. An Excel error and its impacts on public policy debates: In 2010, two economists, Carmen Reinhart and Kenneth Rogoff, published a report claiming that countries with High Debt/GDP ratios have lower growth on average. To support their argument, they used data from 20 advanced economies and calculated their average rate of GDP growth. However, they neglected to select 5 countries (Australia, Austria, Belgium, Canada and Denmark) with both high Debt/GDP and GDP growth rates, skewing their result and the conclusions they draw. This mistake had profound implications. Congressmen and others within the federal government cited this as proof that our federal deficit each year needs to be reduced by cutting a variety of programs, so that our economic growth rate may remain unaffected.

While this is not strictly a GDP error, it shows how a small mistake in calculating GDP data can seriously affect the conclusions drawn from it.

5. US quarterly GDP revisions: For the first quarter of 2014, US GDP was revised downward a couple of times, each time suggesting that the GDP contracted further on an annualized basis. Much of the downward trend is the result of less-than-expected consumer spending on healthcare, and the lackluster performance of exports. In part, the GDP contraction was due to an exceptionally cold winter in the US.

6. Bank of Canada’s forecasting errors: Even in developed countries, economic forecasts can often go wrong. The Bank of Canada (Canada’s central bank) failed to forecast the small economic downturn in the fall of 2012. The bank of Canada’s forecasts are often overly optimistic. Out of 5 of 7 time periods studied, the average economic growth forecast is 0.6 percentage points higher than the actual; and 75 per cent of medium-term forecasts by the Bank of Canada were overly optimistic.

So here it is. So the next time you hear in the news about GDP figures, remember that GDP is a number that’s created by people. Most often, these numbers are correct and give a good picture of our nation’s economic health. But at times, we base our GDP figures, past or future, based on faulty or incomplete information. And sometimes, we make plain simple mistakes.