Monday, January 24, 2011

"Scorecasting:" is home field advantage just biased officiating?

There's a new book that's about to come out, that you might have heard about. It's called "Scorecasting," and the publisher was kind enough to send me a review copy. It's basically a Freakonomics for sports, in intent, in tone, in writing style, and even down to its similar authorship -- one academic economist (Tobias Moskowitz, a finance professor) and one journalist (Sports Illustrated's L. Jon Wertheim).

The book's website is here; it has an excerpt from one of the chapters, and you'll find other excerpts online if you search the authors' names.


The topics will be very familiar to sabermetricians and regular readers of this blog. There are chapters on the Hot Hand, on competitive balance, on NBA refereeing, on steroids, and so on. There isn't a huge amount of breakthrough stuff there, although there are certainly a few new insights. Mostly, the authors summarize what they've learned from academic articles on sports, and they add the results of a few little studies they did themselves.

Alas, by concentrating on the journals, they've missed much of the scholarship of us amateurs. For instance, in the chapter of competitive balance, they argue that baseball is less balanced than the football because MLB teams play 162 games, while NFL teams only play 16. That, of course, is only a small part of the story. There are other parts, such as the distribution of talent in the league, and the internal details of the game itself. Tom Tango has effectively solved the problem of comparing different sports (here's just one of his many posts), but the authors seem unaware of that (although they do mention Tango in the book once, in a mention of leverage, referring to him as a "stats whiz.")

And they're occasionally completely off, as when they say the sample size of the MLB playoffs is enough that the best team ought to win the series.

Still, a lot of the material is solid; the authors are at their strongest when they're reviewing one of the more famous and established studies, like the Romer "fourth down" paper, and the Massey/Thaler NFL draft study. (I'll probably do a full review of the book later, but, for now, just picture a sports Freakonomics that's not as rigorous as most of the websites, but does mention a few things that you didn't know before.)

Anyway, I'm going through the book, and suddenly I see that the authors claim to have solved the problem of what causes home field advantage (HFA). That was sort of shocking. My personal subjective view is that HFA is the biggest unsolved problem in sabermetrics, and very little progress has been made. There's so little progress, in fact, that I've started to take seriously a hypothesis that seems way off the wall -- the theory that humans have built in evolutionary programming that makes them more physically and mentally effective when defending their own turf. (I'm not saying that it's necessarily true, just that I have a bizarre attraction to it.) In that light, finding these HFA claims was a bit like picking up a newspaper article on math, and finding that the reporter has proved Fermat's Last Theorem.

So what's the authors' solution to the long-standing HFA conundrum? Refereeing. After dismissing most of the usual suspects (fan enthusiasm, travel, tailoring the team to the park), Moskowitz and Wertheim believe that most, or all, of HFA can be explained by biased officiating.

They list a bunch of supporting evidence, which I'll summarize here. If you want to follow along, some of this stuff is also in a long excerpt from the book that appeared a couple of weeks ago in the Jan. 17 issue of Sports Illustrated (the article, unfortunately, does not appear to be online).

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Soccer

1. In soccer, the referee controls how much extra "injury time" is added to the end of a match. It turns out that injury time is longer when the home team would benefit. When the home side was ahead by a goal, there were two minutes of injury time, on average, in a sample of Spanish league games. But when they were *behind* by a goal, it was four minutes.

2. In 1998, the point structure changed to give the winning team three standings points instead of two. Immediately, the above injury time bias increased.

3. The same bias exists in England, Italy, Germany, Scotland, and the US.

4. "... home teams receive many fewer red and yellow cards even after controlling for the number of penalties and fouls on both teams."


Baseball

5. In baseball, the authors looked at the percentage of called pitches that are strikes. In crucial situations (high leverage), home teams got a lot more favorable calls. But in low-leverage situations, it was *road* teams that got more favorable calls. "This makes sense," the authors write. "If the umpire is going to show favoritism to the home team, he or she will do it when it is most valuable -- when the outcome of the game is affected the most. You might even contend that it noncrucial situations the umpire might be biased against the home team to maintain an overall appearance of fairness."

6. " ... the success rates of home teams in scoring from second base on a single or scoring from third base on an out -- typically close plays at the plate -- are much higher than they are for their visitors in high-leverage/crucial situations. yet they are no different or even slightly less successful in noncrucial situations."

7. Over a large sample of 5.5 million pitches, "called strikes and balls went the home team's way, *but only* in stadiums without QuesTec ... Not only did umpires not favor the home team when QuesTec was watching them, they actually gave *more* strikes and *fewer* balls to the home team. In short, when umpires knew they were being monitored, home field advantage on balls and strikes didn't simply vanish; the advantage swung all the way to the visiting team."

8. In low-leverage situations, even in non-QuesTec parks, there was no bias at all.

9. The authors then analyzed pitches using Pitch f/x data, to see how many pitches were miscalled based on the recorded location. For pitches on the corner of the strike zone, there were more miscalls in the home team's favor than in the visiting team's favor. The home advantage was largest on full-count pitches, followed by other three-ball counts, other two-strike counts, and, lastly, all other counts. So, the more crucial the pitch, the greater the HFA.

10. "Over the course of the season, all of this adds up to 516 more strikeouts called on away teams, and 195 more walks awarded to home teams than there otherwise should be, thanks to the home plate umpire's bias. And that includes only terminal pitches -- where the next called pitch will result in either a strikeout or a walk. Errant calls given earlier in the pitch count could confer an even greater advantage on the home team."

11. "This adds up to an extra 7.3 runs per season given to each home team by the plate umpire alone. That might not sound significant, but cumulatively, home teams outscore their visitors by only 10.5 runs in a season." [That latter number isn't correct ... in 2010, it was 23.5 runs. 23.5 runs equals 2.35 wins out of 81, which is a .530 winning percentage. (UPDATE: Oops! I forgot to adjust for the home team not batting in the bottom of the ninth when leading. If you adjust for that, the home advantage is a lot bigger than 10.5 or 23.5 runs.)]


Football

12. In the NFL, "Home teams receive fewer penalties than away teams -- about half a penalty less per game -- and are charged with fewer yards per penalty. Of course, this does not necessarily mean officials are biased. But when we looked at more crucial situations in the NFL ... we found that the penalty bias [increases]."

13. When instant replay came to the NFL, the home winning percentage declined from 58.5 percent (1985-98) to 56 percent (1999-2008). "Before instant replay, home teams enjoyed more than an 8 percent edge in turnovers ... When instant replay came along ... the turnover advantage was cut in half." Also, "the home team does not actually fumble or drop the ball less often than the away team ... they simply lose fewer fumbles than away teams. After instant replay was installed, however, the home team advantage of *losing* fewer fumbles miraculously disappeared, whereas the frequency of fumbles remained the same. ... In close games, where referees' decisions may *really* matter ... home teams enjoyed a healthy 12 percent advantage in recovering fumbles. After instant replay was installed, that advantage simply vanished."

14. After instant replay, there was no change in the relative frequency of home and away penalties. That might be because penalties can't be challenged.

15. Away teams have their challenges upheld 37 percent of the time, versus 35 percent for home teams. But when the home team is losing, the visiting team wins 40 percent, versus only 28 percent for the home team. So it looks like the referees favor the home team more when they need it more.


Basketball

16. In the NBA, fouls and turnovers that are not subjective referee calls (like shot clock violations) are equal for home and road teams. But for subjective calls, away teams get between 1 and 1.5 more of those per game. Visiting players are 15 percent more likely to be called for traveling than home players.

17. "How much of the [HFA] in the NBA is due to referee bias? If we attribute the differences in free throw attempts to referee bias, this would account for 0.8 points per game. If we gave credit to the referees for the more ambiguous turnover differences ... this would also capture another quarter of the home team's advantage. Attributing some of the other foul differences to the referees and adding the effects of those fouls (other than free throws) ... brings the total to about three-quarters of the home team's advantage. And, remember, scheduling in the NBA [visiting teams play more back-to-back games than home teams] explained about 21 percent of [HFA]. This adds up to nearly all of the NBA home court advantage."


Hockey

18. In the NHL, home teams get 20 percent fewer penalties and receive fewer minutes per penalty. "On average, home teams get two and a half more minutes of power play opportunities ... than away teams. That is a *huge* advantage." If you multiply that by a 20 percent success rate, you get an extra 0.25 goals per game for the home team. Since the average overall differential is only 0.3 goals for the home team, "this alone accounts for more than 80 percent of the home ice advantage in hockey."

19. There is no apparent HFA in shootouts, where refereeing makes no difference. Also, in NBA foul shooting. And, even in Pitch f/x data. Visiting pitchers throw no worse, according to Pitch f/x, than home teams do. It's only the umpires' calls that are different.

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It's an impressive array of evidence and argument. But, at least some of it doesn't hold up.

Look at number 5: in baseball, in low leverage situations (I believe this means the bottom 50%), the authors say that umpires favor the visiting team. That would mean that, in less critical situations, we should find a "visiting field advantage." But home teams outscore visiting teams even in medium-leverage situations. For instance, here's the breakdown of home and road runs scored by inning (1954 to 2007). The last column is the percentage by which the home team outscored the visiting team:

1 61872-52071 +18%
2 46823-42539 +10%
3 53590-48188 +11%
4 53357-49593 +8%
5 53203-48448 +10%
6 54401-50603 +8%
7 52231-48641 +7%
8 50451-47781 +6%

You would think that you'd have more high-leverage events in the later innings -- but the HFA goes *down* in the last few innings, not up.

But I might be wrong about that, maybe the eighth inning has no more high-leverage situations than the first inning (after all, there are more 8-1 games in the eighth than in the first). So, let's look at innings where, at the start, one team was at least four runs ahead of the other. Those should all be low leverage, for the most part, and should show the visiting team having the advantage.

Nope:

2 2543-2139 +19%
3 4583-4176 +10%
4 8817-7801 +13%
5 10940-10057 +9%
6 14371-13279 +8%
7 15698-14583 +8%
8 16935-16180 +5%

Now, this could be just because, in a four-run game, the home teams are a lot better than the visiting teams. What if we look at situations when the *visiting* team is ahead by at least four runs? Then, we should see a huge effect in favor of the visiting team: first, they're probably a much better team, and, second, the low leverage means the umpire should still be favoring them.

But, no. Even in those situations, the home team still performs a little better, on average, having the advantage in five of the seven cases:

2 957-1022 -6%
3 1974-1799 +10%
4 3609-3355 +8%
5 4435-4645 -5%
6 6269-5705 +10%
7 6627-6562 +1%
8 7309-7179 +2%


So, I just don't see it. If umpires DO call more strikes for visiting teams in low-leverage situations, maybe that's compensated for by those pitches actually being strikes ... but being worse pitches in location and movement and velocity. That is, maybe HFA comes from pitchers throwing more accurately, but more hittably.

In any case, if my data are correct, and the authors' data are also correct, it can't be the case that the authors' findings are an explanation of HFA.

------

Now, let's look at number 18, the hockey case. The authors argue that HFA is caused almost entirely by penalties. If that's the case, then you'd expect home and visiting teams to have similar numbers at equal strength.

They do not. The NHL.com website has home/road goal breakdowns. Here they are for the 2008-09 season, averaged by team:

Even strength... 124-110 (home advantage 12.5%)
Power play...... 35-30 (home advantage 15.1%)
Shorthanded..... 4-4 (home advantage 1.0%)

There's almost as large an advantage at even strength as there is on the power play. Admittedly, the extra power play boost is probably caused by more penalties, as the authors say, but the overall contribution of the extra penalties seems to be pretty small.

Just to make sure it wasn't a fluke, I ran the same numbers for 2009-10:

Even strength... 121-106 (home advantage, 13.9%)
Power play...... 30-25 (home advantage, 21.0%)
Shorthanded..... 4-3 (home advantage, 32.9%)

A bit more extreme in favor of power play. But how do you explain the sizeable advantage for home teams at even strength? One possible explanation is that visiting teams have to play an overcautious game, to avoid being penalized by biased referees. But for a 13.9% disadvantage, that caution would have to be way out of line, wouldn't it?


------

Both of these examples -- and, by the way, they're the only two I checked -- cast doubt on the authors' hypothesis that HFA is almost all refereeing. I have never disagreed that *some* of it might be refereeing, but there's obviously a lot more going on.

And I have to say that the authors have indeed provided a blueprint for how this kind of research should go -- try to break down performance into its constituent parts, and check those.

If there's no home advantage in foul shooting, why not? If there's no HFA in hockey shootouts, why not? If we get a list of areas with high HFA, and a list of areas with low HFA, we can maybe start narrowing down what the causes might be.

But the authors have amassed a lot of evidence, and the must be something to at least some of it, no? For instance, I can't think of any explanation for the injury time phenomenon (maybe I should look up the relevant study). And it seems reasonable that referees will call more fouls on visitors, even if they're unbiased. Why? Because they might be using crowd noise as a guide ot what is and what isn't a foul. If the fans scream when a visitor trips an opponent, but not when a home player trips an opponent, that will simply make it more likely that an unbiased referee will have enough evidence to correctly "convict" the visiting player.

But the question is not just whether referee bias exists, but *how much* of it there is, and how much of HFA it's responsible for. The authors of "Scorecasting" seem more focused on "existence" evidence, and it seems to me they've made only a small dent in terms of explaining the real-life observed HFA. I wish the authors had provided more details of some of their findings, so we can figure out what's going on and maybe quantify it a bit more ... but I guess it is what it is.

I know there are a lot of working sabermetricians reading this ... if you have expertise or evidence on any of the authors' points, please weigh in.

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UPDATE: I have a full review of the book here.


Labels: ,

30 Comments:

At Monday, January 24, 2011 8:19:00 PM, Anonymous Anonymous said...

This is a fascinating topic, thanks.

One thought is that if HFA is due to officiating, then we ought to expect some variance among individual refs.

By variance, I mean between an individual ref's calls between home and away teams.

The reasoning is that some refs ought to be more influenced by the stands than others.

 
At Monday, January 24, 2011 8:53:00 PM, Blogger Phil Birnbaum said...

Yeah, that's a good point, wish I had thought of that. You'd think over all the umpires, there'd be at least one who bucked the trend and treated both teams equally. Is there?

 
At Monday, January 24, 2011 11:16:00 PM, Blogger Mike Fast said...

The home-visitor strike zone has been looked at pretty well by Dan Turkenkopf. The effect he found was not nearly big enough to explain all of the home field advantage.

Dan's work is here:
http://www.beyondtheboxscore.com/2008/4/24/459913/a-strike-is-a-strike-right

I'm very skeptical when non subject matter experts try to tackle the strike zone. It's too complicated for that.

 
At Monday, January 24, 2011 11:24:00 PM, Blogger Phil Birnbaum said...

Thanks, Mike, appreciate the link.

Dan found one run every eight games. That's 10 runs per 81 home games, and 10 runs per 81 road games. So that's 83-79, which is .512.

If baseball HFA is .540, then umpires are 30 percent of HFA, which is still pretty significant.

 
At Monday, January 24, 2011 11:26:00 PM, Blogger Brian Burke said...

Regarding football:

12. This should be expected to some degree. The phenomenon is most noticeable in basketball, but it exists in football too. If I'm being outplayed, it's rational for me to risk playing at the margin of the rules. For football, this means holding, pass interference, illegal contact. So if HFA is present due to some other cause, it would also manifest in terms of penalties. This would not necessarily indicate bias by the officials. #14 would also be consistent with this explanation.

13. The turnover statistics cited is hard to believe on their face. Turnovers are *enormously* decisive in NFL football. A halving of the differential between home and away teams would cause a much greater than a 2.5% drop in the HFA effect. Also, there are only 256 regular season games per year in the NFL. The home team win % in any given year varies greatly. Depending on where you draw your cutoffs, you can get considerable differences in the estimate of the HFA effect.

15. If I understand this correctly, this can be explained by the same mechanism as #12. If a home team is losing, it's challenges *should* be successful less often. The more desperate a team, i.e. when they are losing, the more likely they are to challenge marginal plays. Those marginal plays are less likely to be overturned, as the authors report.

The authors report the difference when the home team is losing, but what about when the visiting team is losing? Do they report that? I'd expect a similar difference due to the 'desperation' factor.

 
At Monday, January 24, 2011 11:33:00 PM, Blogger Phil Birnbaum said...

Brian, thanks. IIRC, the authors do mention the "bad teams might take more penalties for other reasons" theory, but they dismiss it because non-subjective calls seem equal for both teams. Like you, I don't find that all that convincing.

Also, I don't think the authors do mention if there's more successful home team challenges when the home team is winning. However, the overall stats are 37/35 visitors, and the home losing is 40/28 visitors, so the visitor winning is probably around 34/42 (assuming 50:50 distribution, which it probably isn't really).

 
At Monday, January 24, 2011 11:36:00 PM, Blogger Phil Birnbaum said...

BTW, Brian, not sure if you've seen the book ... you're quoted in the NFL Overtime chapter. None of your analysis, just that you found 61% winners among teams who receive, and that's a big advantage, 3:2 odds.

 
At Monday, January 24, 2011 11:48:00 PM, Blogger Brian Burke said...

Well, ok, if they cited me, then I completely change my mind. I totally agree with the authors!

There's a way to test their theory. We can look at sports in which officials have no subjective impact. High school track perhaps? Archery? It's hard to think of sport that's purely objective.

 
At Monday, January 24, 2011 11:54:00 PM, Blogger Phil Birnbaum said...

I think it's interesting that there's no HFA in foul shooting or NHL shootouts. And I think Guy once said there's no HFA in penalty kicks either.

Those have two attributes: no referees, and a very simple chain of events.

Maybe there IS an HFA in those things, just a very small one, perhaps too small to detect without a huge database. And maybe the HFA is bigger in other things because you have a very large chain of events, and a .005% increase multiplies out over the entire chain.

If a visiting soccer team makes their passes 90% of the time, and the home team succeeds 90.5% of the time, the home side will complete a chain of 10 consecutive passes 5.7% more frequently than the visiting side.

It makes sense that HFA on fouls should be low, because it's just one event. But it *doesn't* make sense that it should be zero.

 
At Tuesday, January 25, 2011 12:16:00 AM, Blogger Phil Birnbaum said...

Mike Fast: Wait a sec ... shouldn't the Dan Turpenkopf study have said one run every 16 games, rather than one run every 8 games?

150 called pitches per team is two games, not one game.

That would make the called-pitch issue 15% of HFA, rather than 30%.

 
At Tuesday, January 25, 2011 7:04:00 AM, Anonymous Haakon said...

about HFA in an 'objective' sport

http://sabermetricresearch.blogspot.com/2007/03/home-field-advantage-in-speed-skating.html

 
At Tuesday, January 25, 2011 8:38:00 AM, Anonymous Guy said...

Overall, it sure looks like a lot of cherry-picking going on here, or at least confirmation bias. I don't doubt that referees play some role in HFA, including ball/strike calls. But the authors have clearly gone looking for evidence on one side, and a lot of it is either overstated or wrong.

One thing I don't like is switching from leverage when analyzing some baseball elements, but then switching to count for the pitch f/x data. Are they fishing for patterns in the data, or is there a reason to change the criteria?

The point Brian makes about losing teams committing more fouls also applies to basketball. And the reason it doesn't show up on "objective" fouls is because those violations don't tend to help a losing team (e.g. a losing basketball team needs to shoot quickly, not use the full 24 second clock).

The Questec findings are interesting if true (I don't have 100% faith in anything they report). But Questec is team-specific, so you can't just look at HFA in Questec vs. Non-Questic parks. The Questec teams could just happen to have worse pitchers and/or hitters. You would have to compare teams' home and away K:BB ratio, and then see if Questec park teams had a smaller home performance bump relative to their road performance. I think you might find something, but not enough to explain all of HFA.

And the scoring from 2B/3B rates (if true) don't tell us much. Very few of these plays involve a close call by an umpire. Much more likely that this is just a manifestation of HFA: home batters hitting the ball farther, visiting OFs being positioned less well for throws, home 3B coaches having better read on depth of hits and sac flies, etc.

 
At Tuesday, January 25, 2011 12:21:00 PM, Anonymous Anonymous said...

I think that suggested link between HFA and officiating is pretty weak, at least in soccer. At least in the English Premiere League (EPL) the added time bias, if there is one, seems to favor the big teams or the team favored to win not the home team. This is probably true and is likely due to the fact that soccer refs are trained to allow an attack to continue before stopping play. If it is behind or tied the better team, will press the attack and will most likely be able to continue the attack for some time before the weaker team gets the ball out of the danger zone. When the weaker team is behind, it will try to attack but will more than likely give up the ball and allow the ref to stop the game. Weaker teams and visiting teams are more likely to settle for a tie than are stronger teams or home teams. Again leading to some bias in added time.
Yellow and red cards are too infrequent (1.5 yellows/game and about 0.1 red/game in the EPL and about 2.5 yellow/game and about 0.2/game red in la liga) (see Soccer by the Numbers to have much effect.
Soccer by the numbers looked at bias in home/visitor fouls called and didn't see any, in fact some refs favored the visitors.
Bottom line, at least for soccer, is that refs don't seem to play much role in HFA.
Les

 
At Tuesday, January 25, 2011 12:30:00 PM, Anonymous Eric said...

As far as penalties in the NFL, I'm pretty sure I've heard that in Seattle the crowd noise causes something like 3 false starts a game. That number is higher than average, and I don't know that average, but still, false start is a penalty that is called far more often on the away team. If the overall difference is only 1/2 a penalty per game, does that mean that refs are actually calling more non-false start penalties on the home team?

 
At Tuesday, January 25, 2011 3:49:00 PM, Blogger Mike Fast said...

Phil, I agree that Dan's finding is that the strike zone advantage is about 15% of home-field advantage.

How you want label a game is perhaps a matter of semantics. There are are about 150 called pitches in one game for both teams.

 
At Tuesday, January 25, 2011 4:17:00 PM, Blogger Phil Birnbaum said...

Anonymous 12:21: Doesn't the amount extra time get announced immediately after 90 minutes? In that case, you could look for home bias in that announced time, rather than the actual time, since the "don't end the game during an attack" rule wouldn't affect the announced time.

 
At Tuesday, January 25, 2011 6:09:00 PM, Anonymous Anonymous said...

To follow up on the "objective sports" comment, I have not done any research on this but I'm pretty sure there is a HFA in tennis. When placing bets in tennis tournaments, I believe I have noticed that the betting lines say players from the host country have improved odds of winning. Obviously humans make the initial calls, but with Hawk-Eye human bias should be almost completely eliminated.

I just did a quick google search before clicking post and this came up:

http://summerofjeff.wordpress.com/2010/09/08/home-court-advantage-in-tennis/

 
At Wednesday, January 26, 2011 12:16:00 AM, Anonymous Anonymous said...

Although the added time is announced at the end of regular time, the ref can and often does add additional time often to allow an attack to finish. Or they add time to make up for what the ref sees as time wasting. This extra added time is what many see as bias for the better teams.
In US college and many High School soccer games, time is kept on the scoreboard and and nothing is added. The clock is stopped for goals, cards, and Penalty kicks and for time wasting. Each 45 minute half ends when the scoreboard clock hits 0.
Les

 
At Wednesday, January 26, 2011 12:24:00 AM, Anonymous Anonymous said...

Any explanation of HFA needs to take into account that HFA exists in most sports at all levels of play from youth rec to top pro levels. In games that are played in front of less than a dozen fans and in front of 10s of thousands of fans.
I think that part of the HFA is the old expression play to tie on the road and win at home. Perhaps your idea that we're programmed to protect home grounds isn't too far off.
Les

 
At Wednesday, January 26, 2011 10:51:00 AM, Anonymous Mike said...

I wrote my undergraduate thesis (for the psych department of all things... gotta love hippie college) on the home field advantage, back in 2003. It's remarkable, at that time I had about 7 journal articles I cited, and all of them examined the HFA as though the magnitude of it in each sport (say, 54% baseball, 58% football, 62% hockey, 68% basketball) indicated how strong of an advantage was conferred in each sport. When really, the advantage could be IDENTICAL in each sport, but the actual home team winning percentages are a matter of the magnitude of advantage, as well as the number of trials in each sports' contest.

The one benefit of these journal articles was that they did a good job at ruling out sources of HFA. And if I remember correctly, the only thing that none of them ruled out was the officiating bias and crowd volume. Studies looked at crowd size, crowd density, a bunch of aspects of travel, etc. I looked at stadium familiarity in my study - i.e. did the HFA change from the last year in an old stadium to the first year in a new one? (Answer: no... though of course there are confounds)

In any case, social and behavioral psych will tell you there's a half-dozen well known reasons why a ref would want to please the home crowd, so those explanations have that going for it as well.

 
At Wednesday, January 26, 2011 2:26:00 PM, Blogger j holz said...

Scorecasting was an interesting read but it's clear that the book intentionally presents data in a manner that overstates the impact of various findings.

The authors often throw out some big numbers for how much the percentages are affected by some bias, then say that when they do a new regression to control for factors like team quality, the effect is smaller but still persists. Why not just give the relevant percentages then? Presumably because the deviations are smaller and thus will seem less impactful.

Also, in their baseball HFA section, they assign a value of 7.3 runs per season to home team umpire bias, which accounts for "over two-thirds" of the 10.5 runs per season that home teams outscore their opponents by. First off, I'm not sure where this 10.5 figure comes from; in the Pitch F/X era (2006-10), home teams score 17.8 runs more than they allow.

More obviously damning is that the authors completely ignore the effect of the home team getting less plate appearances because the game ends whenever they have the lead in the middle of the ninth or later. Give them back those plate appearance and the difference soars to 30 runs. Is 7.3 two-thirds of 30?

It's hard to take the rest of the book seriously when they make such basic math errors, although the personality profiles were well-written.

 
At Wednesday, January 26, 2011 2:45:00 PM, Blogger j holz said...

Reading some other comments reminded me of other issues:

- When talking about the Cubs' title drought, they derive the chances that one club in a balanced 30-team league would go title-less in 100 years by a straightforward (29/30)^100 = 3.5% calculation. Of course the Cubs have not been playing in a 30 team league for the vast majority of their 100 years, and the way this is worded in the text seems to imply that there is a 3.5% chance of this happening to any team in the league, rather than just yours.

- The section on competitive balance across leagues is terrible. Baseball gives the underdogs less of a chance to win a title than basketball because of the longer season and only half as many playoff teams? What a joke. Also, the notion that a best-of-7 baseball series gives the better team a bigger advantage than in the NFL playoffs...lunacy. Instead of discussing how gamblers could use these studies to make more money, the authors should try talking to an actual pro sports bettor, who would relieve them of these wrongheaded notions.

 
At Thursday, January 27, 2011 11:23:00 AM, Blogger Wheell said...

There will come a time when our robot overlords will call balls and strikes. At such time I look forward to comparing HFA.

I have to say I'm pretty confident that we are all lowballing the affect umpires/referees play in determining who wins.

 
At Saturday, January 29, 2011 12:17:00 PM, Anonymous Anonymous said...

Regarding what Les said about soccer HFA, I have to add that usually when an away team is winning, they'll intentionally waste time. The authors should (and maybe they did, I don't know) have compared injury/stoppage time to actual playing time. I recall reading once that games won by away teams tend to have less actual playing time than games won by home teams, or tied. This justifies more injury time, in fact.
RS

 
At Saturday, January 29, 2011 1:01:00 PM, Anonymous Anonymous said...

Also, I'll cite these 2 works from BPro. The one by Carleton on the familiarity factor is especially interesting, while Swartz also confirms that early innings offer the biggest gaps in scoring.
http://www.baseballprospectus.com/article.php?articleid=9854
http://www.baseballprospectus.com/article.php?articleid=11292

RS

 
At Saturday, January 29, 2011 9:27:00 PM, Blogger Hawerchuk said...

The authors claim travel distance does not impact HFA, but I found that to be untrue in hockey:

http://www.behindthenethockey.com/2009/12/2/1174752/impact-of-travel-on-offensive

 
At Sunday, January 30, 2011 3:01:00 PM, Blogger studes said...

This was also covered in detail by John Walsh in the 2011 Hardball Times Annual. John found that about one-third of the HFA is due to home plate umpire bias.

 
At Monday, February 21, 2011 12:37:00 PM, Anonymous Jason Lisk said...

Just getting around to seeing this. I've meant to purchase and do a review of this book (alas, no free copy). I saw the claim that HFA was almost all ref bias and was dubious.

My knowledge would be in football, but the authors make a pretty key factual error that I'm guessing got past peer review because they were not subject matter experts.


The NFL had instant replay from 1986-1991. So almost half the seasons they used in the control group had some form of replay.

I talked about it here, in looking at why fumbling rates have declined steadily http://www.pro-football-reference.com/blog/?p=522

 
At Tuesday, September 20, 2011 9:07:00 PM, Blogger Libertarian Realist said...

Baseball's Black Deity

http://libertarianrealist.blogspot.com/2011/06/baseballs-black-deity.html

 
At Saturday, December 17, 2011 9:15:00 PM, Blogger John said...

In basketball, there is an interesting counter-argument to 'HFA due to officiating' in that the advantage seems to increase based on the distance that the visiting team traveled to get to the game. While I have not classified 'long-standing rivalries to see if the teams tend to nearer or further away than average, the correlation of distance to HFA seems to me to indicate that there is a negative affect on players related to travel. The summary of my data is located at the following site:

http://www.whelanlabs.com/home/random-thoughts/home-field-advantage

 

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