ABA equivalents to NBA Win Shares, PER, etc.

[Mike G]

Lots of fans are interested in historic comparisons, and it's never satisfying to see a list of players' "best seasons of the 3-point era", or "best playoffs ever, NBA only". The ABA had many of the best players of the 1970's, and ideally we should be able to compare them to their NBA contemporaries.

http://www.basketball-reference.com/lea ... stats.html

I copied all NBA and ABA players' Advanced Stats from 1965 through 1977 into Excel, sorted alphabetically and by year, and deleted all but those who played in both the NBA and ABA. From these, I retained only consecutive (or closest) player-seasons when one year was in one league and the next year was in the other.

Using the ABA season as reference -- since it was the more rapidly evolving league -- I found average stats for whole groups of [from 9 to 25] players who jumped leagues every year (1968 to 1976). Then from 1976 to '77, about 70 players changed leagues, in the merger year.

From the 1967-68 ABA season -- here called '68 -- some 22 players had at least 100 NBA minutes previously. For 12 of these, one or two years had gone by in the meantime.
Here are their agglomerate stats, from the ABA and from their most recent NBA stints:

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68   Min.    mpg    PER    TS%   eFG%   TRB%  AST%  OW/48  DW/48  WS/48
A   34848   28.6   17.3   .498   .434   9.6   10.3   .078   .054   .132
N   11195   14.4   10.9   .444   .392          9.4  -.008   .041   .037
     Diff:  14.2    6.4   .055   .042           .8   .086   .013   .095
69                              
A    7260   21.7   21.2   .540   .478  11.4   12.3   .122   .059   .182
N    9889   19.6   17.7   .507   .443         13.7   .076   .044   .122
     Diff:   2.2    3.5   .032   .035         -1.4   .045   .015   .060
70                              
A   23224   25.4   15.0   .498   .455   9.3   13.5   .040   .052   .098
N    9141   11.5   11.6   .448   .405         13.4  -.002   .037   .039
     Diff:  13.9    3.4   .050   .051           .2   .042   .015   .059

There are no NBA rebound percents for this era. They could be estimated, though.
Looking at the NBA shooting% and Offensive Win Share rates (OW/48), these had mostly been offensively-challenged players in the NBA, now charged with carrying the offensive load in the ABA. PER and WS/48 well above ABA averages.

The Diff: lines are just A-minus-N values. Most values are positive, in that ABA points and rebounds are easier to come by. Assists not so.

An immediate improvement is shown for the '69 season, only maintained in 1970.
The star quality of the '69 "class" is due to Rick Barry joining the ABA and Connie Hawkins leaving. Barry is compared to his '67 NBA self and Hawkins to 1970.
An assumption here is that the NBA does not change much in the 2-3 years of comparison, and/or that roughly equal player-minutes are being compared to past and future NBA seasons.

This might be called the Early ABA, with huge differences from NBA in what players get in WS/48 and PER.
Next, the Middle ABA era, where the difference is about one-half:

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71   Min.    mpg    PER    TS%   eFG%   TRb%   Ast%  OW/48  DW/48  WS/48
A   12993   23.8   17.6   .523   .481   13.9    9.8   .059   .057   .116
N   10829   19.9   14.8   .499   .451           9.2   .056   .037   .090
     Diff:   3.9    2.8   .024   .029            .6   .004   .020   .026
72                              
A   29020   23.0   15.7   .510   .463   10.4   10.2   .046   .035   .084
N   23861   17.5   13.8   .471   .425    9.5   13.0   .017   .040   .060
     Diff:   5.5    1.9   .038   .038     .9   -2.8   .029  -.005   .024
73                              
A   11748   18.7   15.9   .512   .468   12.7   14.1   .038   .055   .092
N   13668   17.3   14.2   .475   .429   11.1   13.6   .020   .033   .055
     Diff:   1.4    1.8   .037   .040    1.6     .5   .017   .022   .037
74                              
A   16687   27.0   16.8   .545   .500    9.6   14.0   .081   .038   .120
N   15855   18.4   13.7   .484   .442    9.7   14.3   .027   .050   .076
     Diff:   8.6    3.2   .061   .059    -.1    -.3   .054  -.011   .043

Each year's group of league-jumpers has it's unique character: offense/defense, strong or weak rebounders.
Note that by '74, an ABA rebound is just as hard to get as one in the NBA.
After strong gains just 4 years in, the ABA slipped a bit in '73 and 74. This is probably due to some serious defections, along with less domination of the draft.

In the last 2 ABA years, there was major contraction, concurrent with more domination of top draft picks.

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75   Min.    mpg    PER    TS%   eFG%   TRB%   Ast%  OW/48  DW/48  WS/48
A   18536   23.4   14.1   .491   .444    8.8   15.8   .032   .038   .073
N   17072   17.5   13.3   .470   .425   10.2   13.9   .013   .045   .062
     Diff:   5.9     .8   .021   .020   -1.4    1.9   .019  -.008   .010
76                              
A  131288   27.1   15.4   .519   .474   10.1   13.4   .0529  .0518  .1047
N  111018   23.8   15.4   .509   .463   10.6   13.3   .0527  .0517  .1042
     Diff:   3.3     .0   .009   .011    -.5     .0   .000   .000   .001

According to this study, the 1976 ABA was entirely equal to the NBA, in overall quality. Still a bit easier scoring in the ABA, but harder to get rebounds.
And that's mostly the 1977 NBA; I'll bet the 1976 NBA doesn't look this good.

[bchaikin]

in 1976-77, 28% (84/295) of the players in the nba had played in the aba. but of the stats accrued in 76-77, 30% of the points scored (58107/192073), 32% of the rebounds (26816/84886), 29% of the assists (12442/43036), 33% of the steals (5547/16906), and 37% of the blocked shots (3352/9155) were accounted for by former aba players...

[Mike G]

Those are good numbers. I counted 70 players just from the 1976 ABA who made it into the contracted NBA. That's exactly 10 per 1976 ABA team.
You count 84 ABA veterans in the 1977 NBA, so 14 more jumped earlier and were still around.

As for my earlier comments about the ABA dominating the draft, they didn't really miss much in '73 or '74. Rookies from 1968 thru 1976 who were playing in 1977 and who would have careers totaling at least 15,000 total equivalent pts+reb+etc:

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Career equivalent totals

from 1968  NBA                   ABA
28601   Walt Frazier       20983   Louie Dampier
23812   Earl Monroe        19565   Mel Daniels

from 1969  NBA                   ABA
45359   Elvin Hayes        23460   Ron Boone
29856   Wes Unseld
            
from 1970  NBA                   ABA
71440   Kareem AbdulJabbar 25721   Spencer Haywood
26007   Bob Dandridge      16752   Mack Calvin
22036   JoJo White         15236   Willie Wise
17942   Norm VanLier
            
from 1971  NBA                   ABA           
32690   Bob Lanier         38777   Dan Issel
27811   Dave Cowens        24876   Billy Paultz
24947   Calvin Murphy      19198   Charlie Scott
24173   Sam Lacey         
23906   Nate Archibald            
20630   Rudy Tomjanovich            
20319   Pete Maravich            
18794   John Johnson            
   
from 1972  NBA                   ABA               
23451   Randy Smith        49953   Julius Erving
20585   Fred Brown         43292   Artis Gilmore
20127   Sidney Wicks       28753   George McGinnis
17878   Mike Newlin        17393   Tom Owens
15961   Clifford Ray       16706   Dave Robisch

from 1973  NBA                   ABA                
28906   Bob McAdoo         33074   George Gervin
19321   Paul Westphal      17383   Jim Chones
                           16116   Don Buse
                           15578   James Silas

from 1974  NBA                   ABA                  
                           23722   Caldwell Jones
                           19329   Larry Kenon
                           16497   Swen Nater 

from 1975  NBA                   ABA                  
22425   Jamaal Wilkes      49492   Moses Malone
19911   Mickey Johnson     25780   Maurice Lucas
19398   John Drew          23374   Bobby Jones
19196   Truck Robinson     18348   Billy Knight
18275   Scott Wedman            
    
from 1976  NBA                   ABA              
25348   Alvan Adams        20739   Dan Roundfield
23558   Gus Williams       16728   David Thompson
21446   WorldB Free            
15798   Junior Bridgeman            
15182   Darryl Dawkins            

A lot of great rebounders in these last few drafts -- most going to the ABA.

[Mike G]

Here's the compacted summary of annual league-jumpers' ABA-minus-NBA stats.
(The typical ABA player lost this much in each category when playing in the NBA.)

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ABA  mpg   PER    TS%   eFG%  TRB%  AST%  OW/48  DW/48   WS/48  sugg.
1968  14   6.4   .055   .042          .8   .086   .013   .095   .090
1969   2   3.5   .032   .035        -1.4   .045   .015   .060   .060
1970  14   3.4   .050   .051          .2   .042   .015   .059   .060
1971   4   2.8   .024   .029          .6   .004   .020   .026   .030
1972   5   1.9   .038   .038    .9  -2.8   .029  -.005   .024   .030
1973   1   1.8   .037   .040   1.6    .5   .017   .022   .037   .030
1974   9   3.2   .061   .059   -.1   -.3   .054  -.011   .043   .030
1975   6    .8   .021   .020  -1.4   1.9   .019  -.008   .010   .010
1976   3    .0   .009   .011   -.5    .0   .000   .000   .001   .000

Some of these numbers are all over the place, but PER and WS/48 differences are pretty steadily diminishing over the years.
eFG% and TS% are averaged by minutes, not by shot attempts. And so, some of the volatility seen may be just due to differences in yearly sample.
In the suggested column, I've proposed a rate of WS/48 to subtract from ABA players in the associated season. These are rather arbitrary, but at least they don't jump around. Nice round numbers, etc.

Hitting ABA players' WS/48 with this deduction, we get a different ranking for the era's WS leaders. With and without deduction:

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1968-76 NBA + ABA top 20 WS unadjusted       NBA-equivalent WinShares
WinShares  Player           yr    Lg       WS2      Player            yr   Lg
25.38   Kareem Abdul-Jabbar 72   NBA      25.38   Kareem Abdul-Jabbar 72   NBA
22.33   Kareem Abdul-Jabbar 71   NBA      22.33   Kareem Abdul-Jabbar 71   NBA
21.83   Kareem Abdul-Jabbar 73   NBA      21.83   Kareem Abdul-Jabbar 73   NBA
20.38   Wilt Chamberlain    68   NBA      20.38   Wilt Chamberlain    68   NBA
19.78   Artis Gilmore       72   ABA      18.48   Kareem Abdul-Jabbar 74   NBA

18.48   Kareem Abdul-Jabbar 74   NBA      18.23   Wilt Chamberlain    73   NBA
18.46   Artis Gilmore       73   ABA      17.84   Bob McAdoo          75   NBA
18.23   Wilt Chamberlain    73   NBA      17.71   Julius Erving       76   ABA
17.89   Connie Hawkins      68   ABA      17.49   Artis Gilmore       72   ABA
17.84   Bob McAdoo          75   NBA      17.04   Kareem Abdul-Jabbar 76   NBA

17.71   Julius Erving       76   ABA      16.87   Julius Erving       75   ABA
17.58   Julius Erving       75   ABA      16.27   Artis Gilmore       73   ABA
17.14   Spencer Haywood     70   ABA      15.83   Wilt Chamberlain    72   NBA
17.04   Kareem Abdul-Jabbar 76   NBA      15.62   Walt Frazier        71   NBA
16.49   Julius Erving       74   ABA      15.43   Artis Gilmore       75   ABA

16.16   Artis Gilmore       75   ABA      15.33   Bob McAdoo          74   NBA
16.07   Jimmy Jones         69   ABA      15.14   Jerry West          70   NBA
16.03   Zelmo Beaty         71   ABA      15.06   Artis Gilmore       76   ABA
15.83   Wilt Chamberlain    72   NBA      14.95   Walt Frazier        70   NBA
15.74   Dan Issel           73   ABA      14.70   Willis Reed         69   NBA

http://bkref.com/tiny/u8O1H

Before the ABA deduction, it seems 11 of the top 20 WS seasons were in the ABA, in these 9 years.
After docking down the earlier ABA, just 6 of top 20 were ABA. Gilmore with 4, Erving 2.

[Mike G]

Collecting the top 100 Win Shares in individual playoffs, 1968-1976, ABA and NBA, from this page:
http://bkref.com/tiny/ER9uS

Then sorting by best WS/48; and again sorting after converting ABA WS/48:

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WS/48   Player          yr    Tm   Lg   WS     WS/48    Player           yr    Tm   Lg   WS2
.321   Julius Erving    76   NYA   A   3.68     .321   Julius Erving     76   NYA   A   3.68
.310   Connie Hawkins   68   PTP   A   3.98     .297 Kareem Abdul-Jabbar 74   MIL   N   4.69
.297 Kareem AbdulJabbar 74   MIL   N   4.69     .286 Kareem Abdul-Jabbar 70   MIL   N   2.59
.286 Kareem AbdulJabbar 70   MIL   N   2.59     .278   Jerry West        68   LAL   N   3.60
.278   Jerry West       68   LAL   N   3.60     .274   Jerry West        69   LAL   N   4.32
.275   Jimmy Jones      69   NOB   A   2.55     .271 Kareem Abdul-Jabbar 71   MIL   N   3.26
.274   Jerry West       69   LAL   N   4.32     .250   Don Nelson        69   BOS   N   1.81
.271 Kareem AbdulJabbar 71   MIL   N   3.26     .242   Willis Reed       69   NYK   N   2.16
.267   Julius Erving    72   VIR   A   2.80     .237   Julius Erving     72   VIR   A   2.49
.250   Don Nelson       69   BOS   N   1.81     .236   Walt Frazier      71   NYK   N   2.46
.247   Julius Erving    74   NYA   A   2.98     .227   Walt Frazier      72   NYK   N   3.33
.244   Larry Jones      70   DNR   A   2.72     .220   Connie Hawkins    68   PTP   A   2.82
.242   Roger Brown      69   INA   A   3.37     .217   Julius Erving     74   NYA   A   2.62
.242   Willis Reed      69   NYK   N   2.16     .215   Jimmy Jones       69   NOB   A   1.99
.240   Roger Brown      70   INA   A   3.47     .213   Oscar Robertson   71   MIL   N   2.31
.238   Dan Issel        71   KEN   A   3.32     .208   Dan Issel         71   KEN   A   2.90
.236   Walt Frazier     71   NYK   N   2.46     .208   John Havlicek     74   BOS   N   3.51
.228   Zelmo Beaty      71   UTS   A   3.32     .205   Wilt Chamberlain  72   LAL   N   3.00
.227   Walt Frazier     72   NYK   N   3.33     .205   Chet Walker       75   CHI   N   1.85
.218   Spencer Haywood  70   DNR   A   2.58     .204   Rick Barry        75   GSW   N   3.09

Again, the list on the right has had ABA WS/48 adjusted by subtracting the amount suggested in the previous post.
-- in unadjusted WS/48, 11 of the 20 best playoffs in the era were ABA.
-- after adjustment just 6 of 20 were ABA.

[Mike G]

OK, forget about those league-jumpers for the moment. Let's look at players who continued in the ABA from one year to the next, and see how their rates changed in one year. Let's exclude younger and older players whose production rates should be rising or falling, respectively.

Limiting to players 24 to 28 years old -- an age range that includes most players' peak and/or plateau -- we avoid the anomalous possibility certain ABA years being heavy on older or younger players. These ages seem to be reliably consistent across large samples.

The first 3 lines summarize players from 1968 who also played (at least 128 minutes) in 1969, and the difference between the rates shown. A positive difference indicates an improvement in the league: if TS% drops, it's become harder to get a good shot; if TReb% drops, it's harder to get a rebound.

A negative entry indicates it's become easier between the first and next year shown.

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yr    Min     PER    TS%   TReb%   TO%   Usg%  OW/48  DW/48  WS/48
68   89846   15.8   .491    9.7   13.8   20.2   .064   .053   .117
69   83177   14.9   .503    9.5   14.7   19.8   .050   .048   .098
68 to 69      .92  -.012    .17   -1.0     .4   .015   .005   .019
                           
69  102621   16.2   .509   10.5   13.8   20.1   .057   .051   .109
70  100950   16.1   .516   10.7   14.7   19.9   .061   .051   .111
69 to 70      .13  -.007   -.21   -1.0     .2  -.003   .000  -.003
                           
70  113126   16.4   .519   10.1   14.4   20.5   .064   .050   .113
71   99014   15.2   .518    9.7   14.3   19.9   .054   .044   .098
70 to 71     1.19   .001    .34     .0     .7   .009   .006   .016

yr    Min     PER    TS%   TReb%   TO%   Usg%  OW/48  DW/48  WS/48
71   96678   15.1   .516   10.2   14.4   19.5   .049   .049   .097
72   91924   14.3   .522    9.1   14.8   19.2   .051   .044   .095
71 to 72      .73  -.006   1.09    -.4     .4  -.002   .004   .003
                           
72   86061   14.6   .527    9.0   15.1   19.1   .057   .047   .103
73   81045   15.1   .531    8.8   16.0   19.9   .056   .050   .106
72 to 73     -.44  -.004    .15    -.9    -.8   .001  -.004  -.003
                  
73   69460   15.6   .532    9.4   15.7   20.1   .059   .049   .108
74   62132   14.9   .509    9.1   15.7   19.5   .055   .045   .098
73 to 74      .70   .023    .34     .0     .6   .004   .004   .009

yr    Min     PER    TS%   TReb%   TO%   Usg%  OW/48  DW/48  WS/48
74   83720   15.6   .519   10.5   15.8   19.5   .059   .052   .111
75   77411   15.6   .536   10.0   15.4   19.8   .065   .051   .116
74 to 75     -.01  -.017    .58     .4    -.3  -.005   .001  -.005
                           
75   61939   16.8   .550   11.5   15.1   19.6   .078   .060   .138
76   56671   16.3   .531   11.0   15.1   19.5   .068   .054   .122
75 to 76      .53   .019    .51     .0     .2   .010   .006   .016

With the large sample of 1976 ABA players moving on to the 1977 NBA, we pretty much proved those leagues were equal. Now if we work backwards, from 1976 to '75, etc, we can corroborate or refute the results from the league-jumpers' stats upthread.

Sure enough, there's a significant drop in (24-28 YO) players' stats from '75 to '76.
From '74 to '75: very little dropoff. This is inconsistent with the previous study, but that was a much smaller sample.
We see instead a tightening of rates between '73 and '74.

[Mike G]

bump

B-R.com now has BPM for the ABA, but only back to 1974.
Is there any impetus to convert ABA stats to NBA equivalents?

[bchaikin]

Is there any impetus to convert ABA stats to NBA equivalents?

how about a comparison for george mcginnis' 74-75 season? not many players have averaged 14+ reb/g and 6+ ast/g, let alone while scoring almost 30 pts/g...

nor missed 1000+ shots with 400+ turnovers and 200+ steals...

he did alot of everything that year...

or don buse's 75-76 season - 689 ast, 346 steals, just 159 turnovers. he actually had 281 steals his first year in the nba (76-77), but they didn't track TOs yet...

[Mike G]

McGinnis in 1974-75 led a Pacers team to the ABA Finals, was co-MVP (w Erving) before jumping to the NBA.
He had OReb% of 11.4, DReb% of 23.1, Ast% = 22.6, Usg% = 31.7
Nobody else in NBA or ABA has had 10-20-20-30 in these areas in one season.

If we adjust his numbers by amounts delineated upthread, his 1975 line looks like this:

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1975   PER   WS/48   FTr   Ast%   TRb%   ORb%   DRb%  Stl%  Blk%  OBPM  DBPM  BPM  VORP
raw   25.1   .174   .389   22.6   16.9   11.4   23.1   2.9   .9   4.8   1.9   6.7   7.0
adj   23.8   .156   .401   22.3   16.8   10.4   23.4   2.9   .8   3.9   2.0   5.9   6.5
1976  21.3   .139   .414   18.7   15.9    8.5   23.1   3.0   .7   3.4   2.0   5.4   5.5

I've added BPM adjustments, also based on league-jumpers in the last 3 ABA seasons. And McGinnis' 1975-76 numbers with the Sixers.
In almost every case, his '76 rates moved in the direction shown in the adjusted line. Generally by more than expected, as he's moving off his peak year by every measure.