World Bank’s Research Paper
The World Bank research group’s study done in 2010 — Shadow Economies All Over the World: New Estimates for 162 Countries from 1999 to 2007, by Friedrich Schneider, Andreas Buehn and Claudio E Montenegro — is considered to be one of the most authentic report on the unofficial economy across the globe. It estimated India’s shadow economy in 2006 to be 25.1% of GDP, against 22.9% in 1999.
According to the World Bank researchers’ paper: “Shadow economy included all market-based legal production of goods and services that are deliberately concealed from public authorities to avoid payment ....
