I generally don't believe in the concept of a team "getting hot" or "going cold". That doesn't mean a team isn't capable of, say, losing 5 consecutive games after winning 10 of 11; I just think attributing such streaks to the team "being in a groove" is largely misguided (though psychologically convenient).
Let's take winning streaks. How often do you see an otherwise mediocre team rip off 5 consecutive wins and hear people say things like "they're in a zone." I think "being in a zone" or "hitting a groove" almost never* has anything to do with it - I instead believe winning streaks are due almost exclusively to two things:
1) How good the team is (including injuries, suspensions, etc)
So I begin by trying to debunk Hypothesis 1: a team improves its chance of winning a game if it's coming off a win in its previous game.
To evaluate this hypothesis, I looked at the games for each of the 30 mlb teams since the beginning of last season - roughly 210 games per team - to see if their winning % was any different in games when coming off a win as they were overall. Here's the result:
The bubbles to the upper left of the diagonal represent teams that do indeed seem to show a higher winning percentage coming off a win. Well, exactly half of the 30 MLB teams are above the line, half below. The white dot indicates the overall average, which resides barely above the line (overall, MLB teams won 50.6% of games after a win vs 50% of all games overall).
Well, not exactly conclusive, but the fact that the white bubble lies barely above the line doesn't debunk the hypothesis. Maybe a team really does have a slightly better chance of winning a game when coming off a win. Let's continue.
The next step was to look at Hypothesis 2: a team improves its chance of winning a game if it's coming off a win streak (i.e., is "hot"). To do this, I looked at teams' winning percentage after 2-game winning streaks. Turns out such teams won their next game 50.4% of the time, again barely over 50% but slightly less than the 50.6% above. So thusfar, for small 1-game and 2-game streaks, results are still inconclusive and no concrete myth-debunking has occurred.
When I got to 3-game winning streaks, it started to get interesting. The overall win % in the next game after a 3-game winning streak dropped to 47.7%. And this is based on 776 cases, so it seems like a decent sample size (and I mean 'seems' in the strict statistical sense of the word).
So it seems like the hypothesis is taking some hits. Let's keep going. Win % after a 4-game streaks? 45.8%. And after a 5-game streak, it dropped further to 45.5%. I stopped there, as sample sizes beyond 5-game streaks were getting pretty thin.
Add to that the fact that teams with 3-, 4-, and 5-game winning streaks are more often than not among the better teams, and thus would tend to have an overall expected winning percentage greater 50%. This makes their sub-50% win % after streaks even more telling and further weakens the myth. Factoring this in, let's check it out graphical-style:
I won't go so far as to say this proves anything, as a proper analysis probably involves Bernoulli Trials and R squared values and other stuff I'll leave to you mathematicians out there. But the bottom line is if an otherwise mediocre team is coming to LA on a 5-game winning streak, my response will continue to be: "Bring 'em On!"*The '02 A's and '07 Rockies may have been in a zone.
For a related article regarding the '07 Rockies, click here.
For an article debunking the 'basketball-players-with-the-"hot hand"-myth', click here.