Repeating my post from over on the New England thread (seemed appropriate here as well given the talk about SOS and OWP).
Just a word of caution and clarification. Obviously it's next to impossible to do the full SOS calculation on your own. So, yes, just considering the OWP gives you a ball park feel that's pretty useful. But (and I'm stealing my own thunder for an article I'm preparing for the website) there's a few other wrinkles in the calculations that effect the OWP that I don't believe anyone is accounting for (and maybe not remembering or even aware of).
So, it's not even "as simple" as just SOS = 2/3 OWP + 1/3 OOWP.
(1) A team's result against each opponent is removed from each opponents W-L-T record before computing their winning percentage. Now this is relatively minor, so again, for ease and simplicity can be neglected. (The same thing is done for computing each opponent's opponents' winning percentage, the OOWP).
(2) There are multipliers for home and away games that factor each opponent's winning pct. up (away game) or down (home game). (The same thing is done for computing each OOWP). And these factors are not insignificant.
Factored OWP = opponent's winning pct. x SOS multiplier
0.85 for home games (or -15%)
1.25 for away games (or +25%)
So there's a 40% value difference between home and away games. That means that playing a team a little over .500 away is as helpful to your SOS as playing a team a little under .800 at home as can be illustrated as follows:
Away game: .543 win pct. x 1.25 home/away multiplier = .677 factored OWP
Home game: .792 win pct. x 0.85 home/away multiplier = .673 factored OWP
Interesting, isn't it? Two teams with a difference in winning percentages of .249 contribute the same to a team's SOS if the better team is played at home and the lesser team is played on the road. What does everyone think about that? The multipliers are pretty drastic, aren't they? And it can really affect a team's SOS if in a given year by happenstance they host most of the top teams in their conference versus playing them away, or vice versa.
So, I do not want to discourage the simple method of collecting the straight OWP (without removing the head-to-head result and without applying the home/away multiplier), but everyone should be aware that these components of the calculations can make the actual numbers somewhat different that the quick and dirty ones being thrown out there. How much different will vary of course. And there's usually going to be some balancing out within each team's calculations. But it certainly could change who has a better SOS among a group of teams.
So things to keep in mind. Maybe the home/away multipliers could be accounted for in the OWP calculations to be a little more accurate without getting too burdemsome. And I hope you'll all still read my upcoming article on D3soccer.com even though I just gave a good chuck of it away!