Why does the GDP omit illegal transactions?

Question

Why does the GDP omit illegal transactions?

Answer 1

The stupid, lazy criminals keep forgetting to send signed reports of their business activities to the government agency that keeps track of the statistic.

Answer 2

Yep, the gov't can't track it, so it would be very difficult to measure.  

There are many countries where illegal economic activity makes up a great deal of the economy.  It was projected, at one time, that about 15% of Italy's economy was black market, underground type stuff -- the government would try to put some rough numbers together (like the 15%), but the main emphasis of gov't is to stop that illegal activity, not measure it.

Answer 3

Because:

1 - they're illegal

2 - illegal means no documentation

3 - no documentation means no record

4 - government cannot record anything without a record

Hence, GDP measurements do not include illegal transactions and there is no way to attribute money flowing in the system from the illegal transaction