So I've been doing some research into prediction intervals - for this purpose, mostly, with how much certainty can we predict that a team will make the playoffs? I'm still a step away from that; I can get a prediction interval on wins for a team, but it's hard to translate that to playoffs specifically. Once I have full team predictions, that will be a little easier.
A note about this: it doesn't include injuries. I haven't found a way to account for those yet, which is skewing the numbers since this is strictly based off of predicted production vs actual production. If we assume that injuries evenly affect each team, each year (which is completely false), then this would hold true. But, I don't have the research to predict injuries, nor do I want to go into the process of finding back-ups for each team. So let's go with that faulty assumption and move on. Anyways, here's what I've found so far:
We can get within 10 wins of a team's record about 94% of the time. Another way to put that, a team will finish with their predicted wins, minus 10, 97% of the time. In other words, if a team is predicted to finish 20 wins above another team, that is a more or less a lock to happen. So if we set the barrier of making the playoffs at 82 wins, a team with a predicted record of 92-60 will make the playoffs almost always. Because of our high percentage of teams making the playoffs relative to the number of teams, this makes sense.
How about those long shots? It works the other way. If a team is predicted to win 72 games, they will finish above .500 only 3% of the time. If a team is predicted to win 65 games, they have a .0038% chance of finishing with 82 wins or more. For those interested, the standard deviation of a season is about 6.36 wins - so roughly 68% of the time, a team will finish within six wins of their prediction.
The unfortunate limitation of this is 1) movement of players, such as adding a free agent, trading, promoting, etc and 2) injuries. That means that the actual variance is significantly higher. However, I think this does have an interesting point - if ur team is predicted to be a bottom-half team, like around 70 wins, ur chances of making the playoffs without significant injuries to the other middle of the road teams (plus none to you) OR a move to improve, is significantly unlikely.