What makes statistics economical reports so varied and different?
Search for `Iran's GDP` in Google, and what you will see is an image representing GDP of Iran, compared to other neighbor countries. It gives us the value of **393.4 billion USD (2015)**.Now in that page simply open some results. From Wikipedia, from World Economics, and other sources. You see values from 300 to 1.3 trillion Dollars.Values are not coherent with each other. As an engineer who is not an economist but understands figures and diagrams, I think these values are so varied that they can not be used in researches as reliable information.I'm working on a proposal, and I need information that can be trusted. What makes such a bold and universally known economical value so varied across data sources?