How are stipends calculated?

Forgive me if this has been discussed before of if I could find the answer somewhere else, but this has been bugging me. I'm a bit of a loner - I have my friends I like to talk to and I like to sit at my home and build. I occasionally get dragged to a club by a friend and I probably get/give 3-10 positive ratings a week since I started in September. I couldn't say exactly what my overall rating is (not terribly high) but my stipend never goes up. It's been sitting at $115L per week (plus my $500L for premium status) since my first or second week.

So my question really is, how many pos. rates do you have to get before your stipend goes up? I really am not asking this to "get out there and rate-farm" but I am curious.

Heh. I jut checked, and yes indeed! It did finally go up this week! A whole $35L!!! But I'd still like to know anyway.