Macro Question: Commercial/Investment vs Residential

[Mike Huang]

Hi everyone,

I have a very high level question for a project I'm doing.

Does anyone have sources or know where I can find information on how big is the commercial/investment real estate market in the US versus people simply buying as homeowners? To be specific, I'm searching for statistics on the aggregated value and/or volume of the transactions in either. 

Global information is also appreciated.

Thank you all in advance!