[beineke]

FYI, over in the Youth National Teams Forum, we've been having an interesting discussion of goalkeepers' numbers.

http://www.bigsoccer.com/forum/showt...threadid=74250

By the way, Moderator -- is it possible to make Stats and Analysis posts appear on the front page? Thx.

[beineke]

Here are the results of the study put together by ChrisE and me. For more detailed discussion, see the link above.

Offside-Adjusted Ratings for 2001-03

1. Metros +4.17% (Howard, Walker)
2. San Jose +2.31% (Cannon, Onstad)
3. Fire +1.93% (Thornton)
4. Crew +1.61% (Presthus, Busch)
5. LA +1.24% (Hartman)
6. NE -0.61% (Sommer, Brown)
7. DC -0.78% (Rimando, Ammann)
8. KC -1.28% (Meola)
9. Colorado -1.61% (Garlick)
10. Dallas -6.05% (Jordan, Countess)

That is to say, the Metros saved 4.17% more shots than you would've expected from looking at the number of times they pulled their opponents offsides.

A few more points:
-- In addition to the numbers above, the 2001 Fusion were at +2.78%, and the 2001 Mutiny were at -5.65% ... note that those numbers are more scattered.

-- If we hadn't adjusted for offsides, the Metros would still be #1, but their lead would be less dramatic. The Crew would be #2, and the Revs would be #9.

-- In a couple of cases (Rimando at DC, Brown at NE), the current keeper has put up markedly better numbers than his predecessor. In other cases, there doesn't appear to be much difference.

[ChrisE]

So, I'm resurrecting a very very old thread, and I'm going to do so rather poorly, but if I don't, it's going to languish here, unfinished, for god knows how long.

So, months ago, I gathered up the 8 seasons of goalkeepr info (less a couple of unavailable TB/Miami seasons), but didn't really have much to do with it. Seeing as I collected these stats months ago, I can't be sure of their accuracy. For offsides, I simply took offsides/games (which is not as good as offsides/minutes, but I'm sorry, I'm not going to go back now and change it); for save %, I removed pk's, and simply took (sog-goals)/sog - that may not be exactly what we're trying to measure, but it should be measuring the same thing across all 8 years.

		Offsides	Save %
Clb	1996	3.22	0.731
Col	1996	6.38	0.725
Dal	1996	2.56	0.820
DC	1996	4.50	0.723
KC	1996	3.13	0.692
LA	1996	3.81	0.787
Met	1996	3.28	0.786
NE	1996	3.19	0.753
SJ	1996	1.56	0.759
TB	1996	2.69	0.790
Clb	1997	2.75	0.803
Col	1997	4.81	0.744
Dal	1997	2.25	0.831
DC	1997	6.34	0.757
KC	1997	2.25	0.727
LA	1997	5.03	0.755
Met	1997	4.31	0.780
NE	1997	4.34	0.717
SJ	1997	3.59	0.719
TB	1997	3.09	0.724
clb	1998	2.16	0.752
Chi	1998	2.09	0.744
Col.	1998	3.72	0.722
Dal.	1998	2.63	0.752
DC	1998	6.25	0.727
KC	1998	2.75	0.697
LA	1998	4.16	0.735
Met.	1998	4.84	0.755
NE	1998	3.25	0.689
SJ	1998	3.16	0.690
clb	1999	1.00	0.777
Chi	1999	2.13	0.778
Col.	1999	2.47	0.802
Dal.	1999	1.63	0.819
DC	1999	5.25	0.760
KC	1999	3.06	0.730
LA	1999	2.63	0.823
Met.	1999	3.47	0.702
NE	1999	5.25	0.722
SJ	1999	2.59	0.743
clb	2000	1.97	0.741
Chi.	2000	2.97	0.727
Col.	2000	2.94	0.749
Dal.	2000	2.69	0.738
DC	2000	3.97	0.683
KC	2000	2.44	0.836
LA	2000	3.13	0.775
Met.	2000	4.19	0.797
Mia.	2000	3.84	0.741
NE	2000	3.69	0.717
SJ	2000	4.28	0.791
TB	2000	4.03	0.804
clb	2001	3.08	0.812
Chi.	2001	3.31	0.810
Col.	2001	4.23	0.772
Dal.	2001	2.31	0.664
DC	2001	3.65	0.691
KC	2001	3.31	0.720
LA	2001	1.77	0.755
Met.	2001	3.42	0.829
Mia.	2001	3.65	0.792
NE	2001	3.35	0.751
SJ	2001	2.96	0.807
TB	2001	4.62	0.720
clb	2002	2.07	0.770
Chi.	2002	3.00	0.792
Col.	2002	2.96	0.724
Dal.	2002	1.82	0.761
DC	2002	2.50	0.802
KC	2002	3.46	0.732
LA	2002	1.93	0.801
Met.	2002	3.82	0.777
NE	2002	4.43	0.751
SJ	2002	3.61	0.796
clb	2003	1.86	0.784
Chi.	2003	2.69	0.788
Col.	2003	3.17	0.746
Dal.	2003	2.10	0.716
DC	2003	2.03	0.808
KC	2003	3.72	0.770
LA	2003	2.83	0.830
Met.	2003	1.83	0.817
NE	2003	4.76	0.712
SJ	2003	2.38	0.786

For all 8 years, we therefore get totals of:

	Offsides	Save %
1996	3.431	0.757
1997	3.878	0.756
1998	3.500	0.726
1999	2.947	0.766
2000	3.344	0.758
2001	3.304	0.760
2002	2.961	0.771
2003	2.738	0.776

We see that offsides/game have been declining significantly over the years (r=-.77), while save percentage has been rising (r=.60).

Using my extremely meager linear regression abilities, I get, from the preceding list, a formula that looks like offsides = 79% - 1.009%*offsides/game.

This, of course, is where I stop. I think the next logical step would be to adjust for the decrease in offsides over time (which I've done, and improves correlation of predicted offsides from .27 to .37), but I'm reluctant to do that without someone's approval. Obviously, I ought to test for significance, but I haven't got the faintest clue how to do that.

[mellon002]

Originally Posted by beineke

By the way, Moderator -- is it possible to make Stats and Analysis posts appear on the front page? Thx.

I know you posted this a while ago but to answer your question the only thing I can think of is BigSoccer live which shows the most recent posts. Did you mean like a part of the blog section?

[mpruitt]

Yeah that was taken care of by Huss during the switch which was great for him. Although I haven't been participating much recently, the forum appears to be really healthy and I will be redoubling my efforts shortly. Another nice thing form the switchover that you'll notice is the ability to have spreadsheets scroll left and right. It makes things we do around here infinately more readable.

In terms of Chris' numbers it's interesting that the save percentages leaguewide haven't changed all that much. The only dip you see is during an expansion year which would seem to make sense. ANother interesting comparrison might be to see how these numbers compare with other leagues. However, I think that the leaguewide goal save percentages could eventually be an interesitng baseline as to looking for what are the chances on average of a shot going in at any given shot.

[ur_land]

Originally Posted by ChrisE

Using my extremely meager linear regression abilities, I get, from the preceding list, a formula that looks like offsides = 79% - 1.009%*offsides/game.

This, of course, is where I stop. I think the next logical step would be to adjust for the decrease in offsides over time (which I've done, and improves correlation of predicted offsides from .27 to .37), but I'm reluctant to do that without someone's approval. Obviously, I ought to test for significance, but I haven't got the faintest clue how to do that.

The regression equation I get for that is slightly different (and by the way, I'm assuming you made a typo and were really trying to predict saves from offside calls/game):

save%=0.8451 - .02646 (off/game)

This equation's r-squared (i.e., the amount of the variance in save% that it explains) is 0.41, which is pretty good. Incidentally, take the square root of the r-squared, and you get r, the correlation coefficient of save% and off/game, which is about .65ish or so. Not too bad of a correlation, but we only have 8 data points).


And here's what the equation means: Offside calls/game is a marginally significant predictor of save% (p<.09). This means that as offside calls/game go up by one, save percentage goes DOWN by 2.6%. More offside calls leads to lower save percetnage.

As to why this is (more aggressive defenses lead to more 1 vs 1 opportunities?), I'm not entirely sure.

You're right, however, that offside calls have been declining over time (the correlation is significant at p<.02). Interestingly, when you control for time (i.e.adjust for the decrease in offside calls over time), the relationship between offside calls and save% is no longer significant (p=.41). So any affect of offside on save% was really a function of offside calls going down over time and save% going up over time. That and the fact that this is a small sample, which is not ideal from an inferential standpoint.

So, bottom line, it looks like there's not really any relationship (in this small sample) between offsides-trap-like defenses and save percentage, once you control for time.

[ChrisE]

Originally Posted by maxim-1

Yeah that was taken care of by Huss during the switch which was great for him. Although I haven't been participating much recently, the forum appears to be really healthy and I will be redoubling my efforts shortly. Another nice thing form the switchover that you'll notice is the ability to have spreadsheets scroll left and right. It makes things we do around here infinately more readable.

I guess. I sort of liked to have 70 entries on a single page. Maybe I just like things being unreadable.

In terms of Chris' numbers it's interesting that the save percentages leaguewide haven't changed all that much. The only dip you see is during an expansion year which would seem to make sense. ANother interesting comparrison might be to see how these numbers compare with other leagues. However, I think that the leaguewide goal save percentages could eventually be an interesitng baseline as to looking for what are the chances on average of a shot going in at any given shot.

The change in the expansion year isn't surprising, but there's no reason I'd have predicted it to go down instead of up. I mean, people generally make the argument about expansion weakening pitching in the majors, but it ought to weaken hitting too - same here, while goalkeeping/defense may have weakened (although Chigao's keeper was Zach Thornton and Miami's was Jeff Cassar - not significantly weaker), I don't see any reason that it would weaken more than offense. What makes it especially strange is that there was no concurrent jump when the league contracted in 2002 (although 1998 was the first year Ian Feuer ever got significant minutes - maybe he can be blamed).

I think it might be interesting to compare these numbers to other leagues, but I'm not sure exactly what it would show you. Higher save %'s don't necessarily mean a league has better goalkeepers or worse strikers - it might be the case that shot selection is different (I believe England takes a lot more low-percentage long-range shots), or defenses have different strategies, or a host of other factors. They would tell you 'or what are the chances on average of a shot going in at any given shot,' but I'm not sure what that tells you.

[JG]

Originally Posted by ur_land

You're right, however, that offside calls have been declining over time (the correlation is significant at p<.02). Interestingly, when you control for time (i.e.adjust for the decrease in offside calls over time), the relationship between offside calls and save% is no longer significant (p=.41). So any affect of offside on save% was really a function of offside calls going down over time and save% going up over time. That and the fact that this is a small sample, which is not ideal from an inferential standpoint.

Why would you need to adjust for the decrease in offside calls over time, unless there's an indication that this is an officiating change rather than a tactical change?

[ChrisE]

Originally Posted by ur_land

The regression equation I get for that is slightly different (and by the way, I'm assuming you made a typo and were really trying to predict saves from offside calls/game):

save%=0.8451 - .02646 (off/game)

Yeah, my bad on the typo. Thanks a lot for the input, ur_land. It looks to me that the difference between our numbers (certainly not slight!) is that you just used the 8 season averages; although I suspect I didn't make it clear, I used the 80 or so individual team-seasons. It doesn't make sense to me to use just the 8 seasons, since you eliminate the teams that would show the most distinct effect.

statistics stuff...

As to why this is (more aggressive defenses lead to more 1 vs 1 opportunities?), I'm not entirely sure.

That was exactly the theory (Marvin Fischer and beineke's, I believe). More offsides traps means more blown offsides traps means better shooting percentage for the shots that players actually get (probably produces fewer shots in general, also).

You're right, however, that offside calls have been declining over time (the correlation is significant at p<.02). Interestingly, when you control for time (i.e.adjust for the decrease in offside calls over time), the relationship between offside calls and save% is no longer significant (p=.41). So any affect of offside on save% was really a function of offside calls going down over time and save% going up over time. That and the fact that this is a small sample, which is not ideal from an inferential standpoint.

So, bottom line, it looks like there's not really any relationship (in this small sample) between offsides-trap-like defenses and save percentage, once you control for time.

Let me here apologize for screwing up and making my initial post unclear, and try to post some results from the regression that I did. R squared in this case is a measly .075 - offsides clearly don't have as significant an effect as a lot of other factors do. Adjusted r squared is even lower, .063, although I don't know what that means. Excel is kind enough to give me a whole lot of numbers I don't understand, but I think (significance F = .011881) means I can pull one of these (p<.02).

I'm still not gonna mess with adjusting for time unless someone gives me some help.

[ChrisE]

Originally Posted by JG

Why would you need to adjust for the decrease in offside calls over time, unless there's an indication that this is an officiating change rather than a tactical change?

One reason that I think it might be useful is that the yearly error in the regressed save percentages correlates very strongly to the average yearly difference from the mean. Maybe this is to be expected, I'm sort of lost, but here's the data:

mean = .759

1996	0.757	-0.002
1997	0.756	-0.003
1998	0.726	-0.032
1999	0.766	0.007
2000	0.758	0.000
2001	0.760	0.002
2002	0.771	0.012
2003	0.776	0.017
Total	0.759	0.000

	Regression	Average
1996	-0.002	0.002
1997	-0.040	0.003
1998	0.292	0.032
1999	-0.043	-0.007
2000	-0.014	0.000
2001	-0.033	-0.002
2002	-0.094	-0.012
2003	-0.124	-0.017

r=.97455