Gabriel Zucman, a Berkeley economist who spends his time studying inequality, faces a big challenge in his research: rich people hide their money, making it harder to asses the true state of both global and within-country wealth gaps.

Zucman tells Business Insider the revelations contained in the Paradise Papers , the latest treasure trove of leaks of offshore tax accounts belonging to the world’s rich and powerful, shows ” we’re only at the very beginning in the fight against tax havens.”

Following the release of the Panama Papers in early 2016 , Zucman worked with two colleagues to estimate that a stunning 10% of global gross domestic product is tied up in tax havens. Now, he may have more adjustments to make.

“What we see in the data is that offshore wealth is super concentrated – the top 0.1% richest households own 80% of it,” he said.

“These Paradise Papers seem to confirm this insight from previous leaks; the main novelty in this new leak is that we see many more Americans in this Appleby file than in the Panama Papers. So it’s not only Russians or developing countries who use tax havens, but basically the very rich from all over the world.”