No, I personally have a lot of difficulties measuring gaps. What you can do—what the U.S. and the U.K. are doing—to measure the tax gap is not focus on international economy but on the domestic, the underground economy and all that. That's what is measured through a tax gap. It's not only the international; it's the overall.
As regards the international only, I'm not sure you can come up with any figure, including on the fraud, on the evasion, precisely because you do not know the amounts that are hidden somewhere. So you have very strong hypotheses, assumptions, that you need to make when you measure a tax gap. This is an interesting avenue, again very difficult, but you don't need it to find or to take the measures, the actions appropriate to put an end to the phenomenon.