Yep, exactly! Any thoughts on opposing this approach?
Also, what you call a key area is referred to as a "sector" in investing. There are many ETF managers that try to track the various sectors, though your easiest bet might be the Sector SPDRs. Their webpage already has a correlation tool if you just want to use theirs:
http://www.sectorspdr.com/correlation/
Simply enter one of their ETFs (eg. "XLF") and look at the correlation of the other Sector SPDRs.
Basically, if you haven't done this kind of stuff before, this not the type of strategy you should start with.