So I was bored and made a quick spreadsheet on excel to see how badly regs hurt your profit, I wanted a quantitative answer after that thread we had about game selecting at the $16s.
You can get it here : http://www.megaupload.com/fr/?d=M0MU3RE7
If there is a better host than that, let me know (I'm an upload noob).
Also don't read the first part if you don't care about the math.
How the Calculation Works
We first calculate, for you and the other regs, what I called your "skill edge" in a game filled with randoms. That is, the ratio between your average prize won and their average prize won (disregarding any rake considerations, the prize is what you win before rake is taken into account). For example, 10% ROI leads to a skill egde of 1.20, meaning you win 1.2 times more than your fellow donk.
Then we consider a game where there are a given number of regs, and use these skill edge numbers in the following formula, that just states the game is zero sum :
Sum over all players [skill_edge(player i) * profit_of_a_random] = Prize Pool
An example with you, one regular, and 7 randoms in a 9-seater $16 turbo on stars, would yield :
(your_skill_edge + other_reg_skill_edge + 7) * profit_of_a_random = 135
From there we calculate the average prize of a random, then deduce yours, multiplicating by your skill edge. And then we get your ROI. Easy game.
Notes about using the spreadsheet
You can toy around as much as you want. Just be careful that you have to input your ROI assuming there are only randoms in the game. So you should be somewhat generous wth yourself (and for the other regs as well), because if you play SNGs with an average of 2 regs at your table with a 7% ROI, well, your ROI in an ideal game is significantly higher. Up to you to work out the guesstimate.
The interesting (and scary) results
Here's a quick summary if you want to just keep a couple numbers in mind. These numbers are pretty insensitive to your ROI, what really matters is the number of players in the game. See how a player just above the average donk can already hurt. Oh and it's pretty linear, the cost of two regs is about exactly two times the cost of a single one as long as the table isn't full of them.
Summary, for 9-seater SNGs
Cost of a good regular (12% ROI) ________ -2,80%
Cost of an average regular (6% ROI) ________ -1,80%
Cost of a barely winning player (2% ROI)_____ -1,20%
Summary, for 6-seater SNGs
Cost of a good regular (12% ROI) ________ -4,50%
Cost of an average regular (6% ROI) _________-2,80%
Cost of a barely winning player (2% ROI) _____ -2,00%
Regs are super costly to your profit. Game select more, and stay out of my games. I'll do the same with yours. kthx.