That is a very good question which is often highlighted in the media. The problem is trying to calculate tax evasion and determine how much money the government is not taking in because of tax evasion.
It is quite hard to be able to say with certainty what we do not know. I would say that a large majority of OECD countries do not calculate the tax gap. Very few countries analyze the tax gap because, indeed, its true nature is not known, which makes it difficult to calculate or evaluate.
As such, our agency and agencies in most other OECD countries have taken another approach. Instead of undertaking a study that could be completely theoretical, we use our resources to do research on the ground and also to invest in tools that could help us recover this money.