Mac vs. PC – Any Real Data?

I am trying to find some data about which is less costly in the long-run, Mac or PC. There are TONS of anecdotal stories about “I had to repair my PC but not my Mac.” and “My Mac comes with software but PCs don’t.” on the internet, but there isn’t much other than that. Does anyone know of any studies that make conclusions based on actual data (repair costs, electric usage, peripheral costs, replacement timing, etc)?