Ratio of interviews to accepteds and how are groups picked

Does anyone know how many groups are invited to interviews relative to the number that are accepted? Is it something like 2 to 1?

I am also just wondering what kind of system is used to pick groups.

Is it like Reddit where all the partners can up-vote or downvote?

Is it like the United Nations where the founders have veto powers?

Is it like American Idol by the sum of votes or is it more like X-factor with three X's and you're out?

It would be interesting to find out what system they use to pick.