Crime, corruption and tax evasion may have cost developing and emerging economies as much as $903bn in 2009, according to a new report by the Washington-based campaign group Global Financial Integrity (GFI) published on Thursday.

Inevitably, given the nature of the subject matter, the report is based on estimated figures. Illicit financial flows – defined by GFI as "the cross-border movement of money that is illegally earned, transferred, or utilised" – neither lend themselves readily to analysis nor leave a convenient trail of paperwork to follow.

Nonetheless, the report suggests that, for the 11th year running, Chinese citizens lost the most. In the decade leading up to 2009, an estimated $2.74tn allegedly left China unrecorded, approximately $291,280m in 2009 alone, the study claimed.

The report suggests that most of the money was lost through "trade mispricing": the over- or underpricing of goods in order to evade tax or transfer funds into another jurisdiction.

The report was written by the economist Dev Kar, who spent 32 years working for the International Monetary Fund (IMF) before joining GFI.

Kar used two methods to calculate the estimated losses. First, he measured the gap between incoming funds and spending. If a country spent less than it received from creditors or through foreign direct investment (FDI), he concluded money had been lost through unrecorded outflows. "At the most simplistic level, supposing a country gets $100, but it's only able to account for $80, then we can say that $20 has left the country unrecorded," said Kar.

Second, Kar looked for trade mispricing by measuring the difference between recorded exports and imports as reported by a country's importing partners. Corrupt exporters under-invoice, while disreputable importers over-invoice. "A classic example of export under-invoicing would be if an Indian company told its government it had exported $5m worth of tea to the US, when in fact it had exported $8m worth of tea," said Kar. "The American importer is then asked to place the remaining $3m into an offshore bank account. This is how companies and individuals send money out of the country."

The 10 countries with the estimated highest illicit outflows in the decade leading up to 2009 were: China ($2.5tn), Mexico ($453bn), Russia ($427bn), ($366bn), Malaysia ($338bn), Kuwait ($269bn), United Arab Emirates ($262bn), Qatar ($170bn over nine years; data for 2000 are not available), Venezuela ($171 bn), and Poland ($160bn). When these estimated figures are averaged out, these 10 countries collectively account for 70% of the illicit outflows from all developing and emerging economies over the period between 2000 and 2009.

According to the report, the entire western hemisphere accounted for just 15.3% of illicit flows in 2009.

GFI's director, Raymond Barker, said he wished he could attribute a 41% fall in illicit flows in 2009 – from $1.26tn in 2008 to $903bn – to stronger governance and increased financial transparency. In fact, he suggested, the fall was due to the recession.

"This is a breathtakingly large sum at a time when developing and developed countries alike are struggling to make ends meet," said Barker. "The need for a combined global effort to curtail illicit financial flows is more urgent than ever. We are pleased to note that the G20, OECD, World Bank, and others are beginning to take this issue much more seriously. This report should be a wake-up call to world leaders that more must be done to address these harmful outflows."