It’s an open secret that many third-world countries, and to a smaller extent, developed countries, are estimated to have parallel economies(PE) that rival, if not surpass, the official economy. I’ve seen some numbers that peg India’s PE to be 1.5-2 times the legitimate economy.
Just how are these numbers determined, given the inherently undocumented nature of the activities that comprise the PE? What’s the confidence that can be invested in such estimates?