tag:blogger.com,1999:blog-38600807.post7365505620037499419..comments2018-06-02T14:19:34.554-04:00Comments on Advanced Football Analytics (formerly Advanced NFL Stats): Momentum Part 5 - Series Level AnalysisUnknownnoreply@blogger.comBlogger7125tag:blogger.com,1999:blog-38600807.post-65490046008474555862014-01-28T10:24:21.584-05:002014-01-28T10:24:21.584-05:00> How many runs would they have, compared to a ...> How many runs would they have, compared to a team with a constant <br />> success rate? ...<br /><br />The runs test can really only be used to reject the assumption of statistical independence. (There might be something happening that hides the impact of momentum in the test.)<br /><br />> For example, imagine a team that had a 75% series success rate when <br />> they were "hot" and a 60% series success rate when they were "cold", ...<br /><br />Let's say teams average 14 first downs per half. Then we'd expect the streaks in the hot half to be:<br />2*( 14*(.75) * 14 * (.25) ) / 14 +1 = 6.25<br />and in the cold half<br />2*( 14*(.6) * 14 * (.4) ) / 14 +1 = 7.72<br />and if the team were average (67.5%) over a whole game:<br />2*(28*(.675)*28*(.325))/28+1= 13.285<br /><br />There's a (.75*.4)+(.25*6)=.45 chance of an extra switch when we put the hot and cold halves together, so the expected hot/cold total is:<br />6.25+7.72+.45=14.42<br /><br />We'd expect the hot/cold team to have about 1.2 more streaks per game. Of course, with this small number of trials, the difference is of limited statistical significance.<br /><br />> That's an excellent point. But I think the runs test methodology will<br />> account for that. One overall success rate is not used in the analysis.<br /><br />I don't see how there could be a statistical difference between the green zone and 'running hot' or the red zone as 'running cold'.Natenoreply@blogger.comtag:blogger.com,1999:blog-38600807.post-24093278435252115192014-01-27T23:11:34.096-05:002014-01-27T23:11:34.096-05:00Nate-That's an excellent point. But I think th...Nate-That's an excellent point. But I think the runs test methodology will account for that. One overall success rate is not used in the analysis. Each particular game's successes/non-successes create the expected # of runs, so it will account for the number of visits to the red zone and other similar factors.Brian Burkehttps://www.blogger.com/profile/12371470711365236987noreply@blogger.comtag:blogger.com,1999:blog-38600807.post-91828735476544062532014-01-27T15:52:13.731-05:002014-01-27T15:52:13.731-05:00I'd expect the end of games to look more strea...I'd expect the end of games to look more streaky, because of changes in strategy (prevent defense, running out the clock, etc.). What do the numbers look like if you only use data from the first 3 quarters?<br /><br />Also, I don't have a clear intuitive sense of what these streakiness numbers mean (e.g., 12.5 runs instead of 13.7). It would be easier to interpret if we could run some simulations of teams with known levels of streakiness (by a more intuitive measure) and see how they came out on that measure. <br /><br />For example, imagine a team that had a 75% series success rate when they were "hot" and a 60% series success rate when they were "cold", and which was cold for the first half of each game and hot for the second half. How many runs would they have, compared to a team with a constant success rate? What would their hot & cold success rates need to be (instead of 75% and 60%) in order to match the observed number of runs?Dannoreply@blogger.comtag:blogger.com,1999:blog-38600807.post-35911981071201519682014-01-27T14:47:53.368-05:002014-01-27T14:47:53.368-05:00> Nate-It depends, obviously. ...
Sorry, I gue...> Nate-It depends, obviously. ...<br /><br />Sorry, I guess I could have been clearer.<br /><br />Let's say -for the sake of discussion- that, on average, the series success rate is 70%, but that there's a 75% success rate outside and then a 50% success rate inside the red zone. Because advancing the ball into the red zone cuts success rates, that means that the trials are not independent, even without momentum as an explanatory factor.Natenoreply@blogger.comtag:blogger.com,1999:blog-38600807.post-16615759373714144942014-01-27T11:39:20.038-05:002014-01-27T11:39:20.038-05:00Have to say I've enjoyed reading your series o...Have to say I've enjoyed reading your series on momentum, probably because it's one of those 'myths' in sport that I just refuse to believe in. I am firmly of the opinion that any evident momentum within the course of a game is a construct of the human mind, trying desperately to cope with the randomness of events and seeking some order in them.<br />The very fact that such huge 'momentum swings' are possible points immediately to the transient and arbitrary nature of the concept.<br />People being people try and make sense of it with a concept such as momentum because we just can't cope with there not being a reason (or at least there not being one better than random streaks of results).<br />Would we do this with coins? Would someone witnessing 7 heads in a row say that heads have 'momentum'? It's unlikely because we essentially know that a coin toss is random. Sports are different, they're supposed to be decided by skill not chance, and so when we witness randomness within them we need some other explanation that might be something to do with the players.<br />Side-tracking slightly, I recently read that 50% of soccer matches are decided by luck rather than skill. Whether this is a reason to despair and wonder why your team bothers acquiring talent when it's half luck anyway, or to celebrate that no matter how bad your team they still stand a chance, is open to debate. I only mention it to highlight the large element that luck plays in some sports leading to mirages like momentum. After all, if it was all down to skill the better team would simply continue to roll to inevitable victory in one constant stream of momentum.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-38600807.post-6340382263712345982014-01-27T11:24:00.441-05:002014-01-27T11:24:00.441-05:00Nate-It depends, obviously. The point is that a 4t...Nate-It depends, obviously. The point is that a 4th down conversion attempt gives a team an additional chance to bridge together multiple "runs" into one "run" if successful. In other words, a successful conversion often turns what would otherwise be 3 or 2 runs into 1 run. I'm not sure if that's an issue or not, but I thought it was worth mentioning.<br /><br />By the way, if anyone is curious, the overall series success rate is around 67% ~ 70%.Brian Burkehttps://www.blogger.com/profile/12371470711365236987noreply@blogger.comtag:blogger.com,1999:blog-38600807.post-55345590802812009822014-01-27T11:09:53.255-05:002014-01-27T11:09:53.255-05:00Is the expected success rate actually 50%? In ext...Is the expected success rate actually 50%? In extreme situations - like attempts to convert 4th and goal from the 6, it seems the success rate would be very low. Similarly, a 4th and 1 conversion attempt on your own side of the field probably has a high success rate.<br /><br />Sure, most of the time, the success rate will be close to 0.5, but it probably doesn't take much to throw off the streak test.<br />Natenoreply@blogger.com