interface – What percent of internet users use mouse back/forward versus the browser back/forward buttons?

I personally almost never use the browser buttons and I imagine it’s the same for most tech savvy users but I want to know what the usage patterns are like for the rest of the population. From my own observation (a very small sample) older people, and non-tech savvy tend to click the browser buttons. It amazes me that there are still many mice on the market that don’t have back/forward buttons. Are the any studies on this?