http://www.canadianbusiness.com/article/43493--undercover-economy by reading this article, can you tell me what is the main claim and its sub-claim?

http://www.canadianbusiness.com/article/43493--undercover-economy by reading this article, can you tell me what is the main claim and its sub-claim? What are the evidences that used to support the claims? Finally, discuss the underlying assumptions that are implicit here.