Silly comparison: number of active developers

Just curious if there's any way to find out roughly how many developers are contributing to core ethereum code, as well as how many are working on apps that would run on ethereum (ie using solidity), as well as how many are building km other blockchains (such as bitcoin).

I'm guessing it's a vanity metric that doesn't really hold much value, but I also figured it was a starting point for comparison of what we can expect over coming 12-24 months in terms of improvements and innovations coming to market.

Thanks for any pointers!