Posted: Thu Jan 27, 2005 10:21 am Post subject: SoapBox: PSA, TS%, ERA??? (Standardization)
I think one of the things we should try to accomplish as a group is to standardize the stats we use. It's important if we want to have non-APBR people try to understand the work we've done, that they can go from one site to the next without a conversion chart.
One thing that has confused me is PSA & TS%. A year ago when I initially tried my hand at stats, I had used the equation PTS/(FGA+FTA) for PSA. I thought the name "points per shot attempt" would be just that. However what Hollinger calls PSA in his book is more accurately described as adjusted PSA (aPSA) because of the .44*FTA factor.
Next, I've thought we came to an agreement to call this TS%,because of Kevin's excellent primer. As Kevin pointed out to me, TS% is half of PSA. I know that as people develop stats on their own, everyone is going to come up with the same stat that is essentially multiples of each other (per 40 minute stats or per 48 minute stats?). However there is no reason to continue with two different stats that are identical. Imagine if baseball had ERA (ER*9/IP) and RAI (runs allowed per inning ER/IP). That's exactly how (for lack of a better word) absurd having two seperate stats are.
Everyone here may know that PSA=TS%*2 (thanks Kevin for bringing me up to speed), but it's hard when you're trying to bring the message to a wider audience. An audience who's statistical knowledge may be limited to FG% and per game stats because that's all they've seen in their basketball coverage. It's even harder when the stats have misleading names likes "points per shot attempt."
So what I'm asking is this:
1. Decide which we should use: PTS/(FGA+.44*FTA) or PTS/(2*(FGA+.44*FTA))
2. Decide what that stat is called. If we use the latter, I think TS% is a fine choice. If the former, we need to come up with a more precise name. (My choice - aPSA)
Joined: 03 Jan 2005 Posts: 295 Location: Greensboro, North Carolina
Posted: Thu Jan 27, 2005 10:50 am Post subject:
I would prefer True Shooting Percentage, i.e. dividing by two. That puts this measure in direct competition with field goal percentage, which is where I think it belongs.
Another option would be to not divide by two, but multiply by 100. That would put it on the same scale as offensive and defensive ratings. That said, my preference is still for True Shootng Percentage.
I also vote for division by 2. We already have a points per attempt-ish number -- Offensive Rating. Let's not confuse the issue: make it a percentage that ranges from zero to 100%, and that's something most people understand intuitively. _________________ ed
I'm only uncomfortable using division by 2, because the Prospectus/Forecast and basketball-reference.com don't. Those are the two "mainstream" sources that use either (that I know of - 82games uses neither).
As a blogger, I have to appeal to a wide audience, and need to use stats that the common fan (read those that don't track their own stats) can identify with an understand. If they don't understand what a .60 TS% is, by not being able to look at players/eras they're familiar with, then for those readers the stat is useless. Without one or both of those switching over, I would feel highly uncomfortable using them.
Joined: 13 Jan 2005 Posts: 103 Location: Iowa City
Posted: Thu Jan 27, 2005 2:09 pm Post subject:
I like PSA because it has a direct meaning. How do you explain TS%? You explain how you estimate points per shot attempt (and what you mean by shot attempt) and then, uh, err, divide by 2. Why 2, why not divide by 3, 2.5, pi, or max PSA?
I don't really have strong feelings on the matter, but just thought I'd put forth an argument for my minority position.
Joined: 03 Jan 2005 Posts: 295 Location: Greensboro, North Carolina
Posted: Thu Jan 27, 2005 2:38 pm Post subject:
Ben wrote:
I like PSA because it has a direct meaning. How do you explain TS%? You explain how you estimate points per shot attempt (and what you mean by shot attempt) and then, uh, err, divide by 2. Why 2, why not divide by 3, 2.5, pi, or max PSA?
I don't really have strong feelings on the matter, but just thought I'd put forth an argument for my minority position.
I think you are overstating your case a bit. We divide by two so it is directly comparable to the competing field goal percentage statistic. Which is precisely the reason why I think we should divide by two. The quicker we run field goal percentage out of business as an important statistic the better.
Joined: 13 Jan 2005 Posts: 103 Location: Iowa City
Posted: Thu Jan 27, 2005 2:57 pm Post subject:
Dan Rosenbaum wrote:
Ben wrote:
I like PSA because it has a direct meaning. How do you explain TS%? You explain how you estimate points per shot attempt (and what you mean by shot attempt) and then, uh, err, divide by 2. Why 2, why not divide by 3, 2.5, pi, or max PSA?
I don't really have strong feelings on the matter, but just thought I'd put forth an argument for my minority position.
I think you are overstating your case a bit. We divide by two so it is directly comparable to the competing field goal percentage statistic. Which is precisely the reason why I think we should divide by two. The quicker we run field goal percentage out of business as an important statistic the better.
But FG% actually is a percentage. What precisely do you mean by "directly comparable"? FG% also happens to indicate 1/2 your PSA if you took no FT's or 3FGs, while TS% is 1/2 your PSA?
I like PSA because it has a direct meaning. How do you explain TS%? You explain how you estimate points per shot attempt (and what you mean by shot attempt) and then, uh, err, divide by 2. Why 2, why not divide by 3, 2.5, pi, or max PSA?
I don't really have strong feelings on the matter, but just thought I'd put forth an argument for my minority position.
I think you are overstating your case a bit. We divide by two so it is directly comparable to the competing field goal percentage statistic. Which is precisely the reason why I think we should divide by two. The quicker we run field goal percentage out of business as an important statistic the better.
Why do we have to make it look like FG% to drive FG% out of business? If anything should replace FG% it's clearly eFG%. I feel that PSA/TS% should be it's own animal, so that it's clearly distinctive from FG%.
I agree with Ben that "PSA" is simple to understand as a function of the number of shots taken. While it's not as simple as PTS/FGA, it's easy to understand that a "PSA" of 1.00 means that if player A is ending the possession by shooting, he's likely to score one point. Similarly that a player with a 1.2 will get 12 points on 10 possessions or a player with a .8 will get 8 on those same 10. You don't get that same feel with TS%, until you multiply it by two. "PSA" is just more intuitive.
Joined: 30 Dec 2004 Posts: 277 Location: Bay Area, California
Posted: Thu Jan 27, 2005 4:15 pm Post subject:
Ben wrote:
I like PSA because it has a direct meaning. How do you explain TS%? You explain how you estimate points per shot attempt (and what you mean by shot attempt) and then, uh, err, divide by 2. Why 2, why not divide by 3, 2.5, pi, or max PSA?
I personally don't use this ____ stat much because I don't like combining FT effectiveness with FG effectiveness except in occasional cases. But when I do, it's to assess a player's ability to both create their shot (FGA + 0.44*FTA, on its own) and how efficient they are. As a consequence, I think of it as a weighted average of eFG% and FT%. If you're looking for an explanation, that's what it is. _________________ Dean Oliver
Consultant to the Seattle Supersonics
Author, Basketball on Paper
http://www.basketballonpaper.com
Joined: 03 Jan 2005 Posts: 295 Location: Greensboro, North Carolina
Posted: Thu Jan 27, 2005 8:22 pm Post subject:
HoopStudies wrote:
I personally don't use this ____ stat much because I don't like combining FT effectiveness with FG effectiveness except in occasional cases. But when I do, it's to assess a player's ability to both create their shot (FGA + 0.44*FTA, on its own) and how efficient they are. As a consequence, I think of it as a weighted average of eFG% and FT%. If you're looking for an explanation, that's what it is.
That's interesting that you think about it that way. I don't like separating FT effectiveness from FG effectiveness. A player does not decide to shoot a free throw. His decision often is whether or to put himself in a position to draw a foul. The cost of putting himself in that position is that he probably is going to shoot a lower percentage on those field goal attempts. Personally I want to capture this tradeoff when I compare a player like Kobe Bryant who draws a lot of fouls to a player like Jamal Crawford who does not. So for me true shooting percentage is a pretty fundamental concept. In contrast, I sometimes look at eFG% and very rarely look at FT%. I almost never look at FG%, except when it is brought up by other people.
I don't like separating FT effectiveness from FG effectiveness.
Yes, I agree with DanR (and with the "divide by two" crowd). I won't quote DanR's whole response but it states the case for combining FTA and FGA very well.
There certainly are times when we'll want to split scoring into two sub-components as DeanO suggests (FG shooting and getting to the FT line and making FTs), but for that matter there are plenty of times when we'll want to split scoring into 3 sub-components (3PT FG%, 2PT or overall FG%, and FTM & FTA), and or even more (fast breaks vs halfcourt, contested vs open, set shot vs shooting on the move, etc.).
But there's other times when a single "effective scoring percentage" is useful, and does away with the need to separately look at FG% stats and FTM stats.
Posted: Sat Jan 29, 2005 12:02 am Post subject: Re: SoapBox: PSA, TS%, ERA??? (Standardization)
KnickerBlogger wrote:
I2. Decide what that stat is called. If we use the latter, I think TS% is a fine choice. If the former, we need to come up with a more precise name. (My choice - aPSA)
Although nobody voted for it in the other thread, I like to call it "shooting efficiency".
What does the "S" is "TS%" stand for? "Scoring" could imply all the things that go into creating a score: not turning the ball over, creating assists, etc. So I prefer "Shooting", because that's what that these stats look at --FG% and FG% -- while ignoring turnovers and assists.
Joined: 30 Dec 2004 Posts: 277 Location: Bay Area, California
Posted: Sat Jan 29, 2005 2:40 am Post subject:
Dan Rosenbaum wrote:
That's interesting that you think about it that way. I don't like separating FT effectiveness from FG effectiveness. A player does not decide to shoot a free throw. His decision often is whether or to put himself in a position to draw a foul. The cost of putting himself in that position is that he probably is going to shoot a lower percentage on those field goal attempts. Personally I want to capture this tradeoff when I compare a player like Kobe Bryant who draws a lot of fouls to a player like Jamal Crawford who does not. So for me true shooting percentage is a pretty fundamental concept. In contrast, I sometimes look at eFG% and very rarely look at FT%. I almost never look at FG%, except when it is brought up by other people.
In all these things, it's a matter of how finely you want to slice it. I like slicing these two right away typically because it's easy. I also find greater significance in my studies when slicing them. If I combine things, significance is harder to find in strategy evaluation. That doesn't mean I don't do it, but I think blending skills can introduce noise that can make it more difficult to find significance. _Can_ make it. In some way, they are the same skill (guys who penetrate), but not for guys who draw a lot of foul shots by going to the boards. And, as always, I am interested in skills and roles more than some measure of overall quality.
I don't have any problem with whatever we're calling this stat. I just choose to keep the ability to draw fouls separate from the ability to make shots most of the time. _________________ Dean Oliver
Consultant to the Seattle Supersonics
Author, Basketball on Paper
http://www.basketballonpaper.com
Joined: 27 Jan 2005 Posts: 206 Location: cleveland, ohio
Posted: Sat Jan 29, 2005 5:21 pm Post subject:
i too like to combine the two, so you are comparing "apples to apples". after all does a coach really care how you score, just as long as you do score?...
i look at any one FGA or two FTAs as each being a single scoring opportunity, and use:
(2pters + 1.5x3pters + FTM/2)/(FGA + FTA/2)
and call this a "Scoring FG%" for lack of a better term, and:
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