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Ang Sun Zhichao Wei Oct 29, 2012
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Transcript of Ang Sun Zhichao Wei Oct 29, 2012
Once a Loser, Always a Loser?The effect of relegation on future career development in the England Soccer
League
Ang SunZhichao WeiOct 29, 2012
Research Question 1
• The effect of job assignment on long-term career development
A signal for future employersOpportunities for human-capital accumulation in the
work place• In the context of economic crisis Oreopoulos, Wacher and Heisz (2012)• Little empirical research on state dependence of
job quality
Research Question 2• Human-capital accumulation in the work placeEmpirical work on evaluating on-the-job
training programsLearning by doing: Argote and Epple (1990)
and Thompson (2010)
We show dominant importance of practice in the soccer industry
The closely-relegated versus closely-non-relegated research design
• Study the state dependence of job quality by exploiting the setting of relegation of the league in England.
• Compare the teams ranked 3rd-last and 4th-last.• Identifying assumption: The team on the
margin but that succeeded in maintaining its position in the Premier League forms a valid counterfactual for the team on the margin but that is relegated to the second-tier league.
Main Findings
• Main findings:No difference in turnover (dropout or transfer)The players in the relegated teams played in lower-
ranked clubs, had more appearances in the first three years after relegation, but eventually played in higher-ranked clubs four years after relegation.
This pattern is driven by players below 30. Older players are worse off in both the short run and long run.
Interpretations
• The relegated team invests less in the transfer market, and players have more appearances in which to practice. This helps the players accumulate human capital (or slows down human-capital depreciation) and land relatively good teams in the future.
External Validity
• Methodological advantages • Interesting and surprising results• The extent of practice, future career development
are easier to measure, and these measures closely mirror that in many immediately relevant domains
• The growing tradition of research that exploits the wealth of data and well-defined incentives in sports to investigate more general economic phenomena( Kotchen and Potoski, 2011)
Background on English football league system---Hierarchical format
1
2
3
4
5
6
7
8
9
18 19 20 21 22 23 24
Hierarchical format
#teams
Hierarchical revenues
• Television revenues shared exclusively among the Premier League members since 92 season
• Huge gap in revenues between the 1st -and 2nd –tier leagues
The average Premier League team receives £45 million, while the average Football League Championship club receives £1 million.
The big effect of relegation on clubs and players
• For clubs Consequent financial problems including, in some
cases, liquidation.• For relegated team players Immediate transfers are restricted Less and lower-quality on-the-job training (-)Poorer facilities and limited access to other
resources (-)Face weaker external and internal competition (?)
-20
-18
-16
-14
-12
-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16 18 20
-100
-80
-60
-40
-20
0
20
40
60
80
100
Figure 2-Propensity of Playing in Premier League
just relegatedjust not relegateddifferences
Normalized year
%
0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 990
20
40
60
80
100
120
Figure 3-Percentage of Players Staying on the Team
just relegatedjust not relegated
Months after relegation season
%
Data
• Focus on the whole career path of those who were once on the margin of relegation
• Step 1 : names of the clubs once on the margin• Step 2 : the quad of each team in the season
when on the margin of relegation• Step 3 : based on the player roster, look for the
player-level information in two relevant datasets to construct a panel by player and by time
Player-level info: data source 1
• Online dataset Soccer Base • Advantage: Rich info Date of birth, birth place, nationality, height, weight,
position, all teams on which player played, the exact period played on each team (including the team he has contract with and the teams he was loaned or swapped to), transfer fee for each transfer he experienced, appearances and goals on each team for which he played.
• Disadvantage Appearances are aggregated to club level
• Records precise time interval for experiences in each club for each player
• Match the data with yearly rankings• Use this data set for the empirical analysis
about the long-term placement of players, including the ranking of the club on which he played and signed up with at each point of change in contract.
Player-level info: data source 2
• Online dataset Player History• Advantage: aggregates players' performance
to each season instead of club• Disadvantage: No info about a loan or swap No record for transfers in the middle of a
season. No info about transfer fee.
• Use data source 2 to examine the change in appearances after relegation.
• The changes can be detected even if a player stays in the same club after relegation.
Summary statisticsSample clubs ranked third- and fourth-last during 1992-2002
#clubs 1610 On the margin
once
6 On the margin twice
#players 670By position
36.10% Defense21.9% Forward
11.03% Goal Keeper30.66% Midfield
By nationality64.24% England35.76% Others
Career length (yrs) 17.036 (8.425)#transfers 6.272 (3.521)
Third- last versus fourth-last teams19
5019
5219
5419
5619
5819
6019
6219
6419
6619
6819
7019
7219
7419
7619
7819
8019
8219
8419
8619
8819
9019
9219
9419
9619
9820
0020
0220
0420
0620
0820
10
0
20
40
60
80
100
120Figure 1-Points by rankings in the Premier League
Champion
4th lowest team
3rd lowest team
1st lowest team
Poin
ts
Player characteristics Teams closely relegated Teams closely not relegated
Difference(1)-(2)
(1) (2) (3)
Height 1.808[.0036]
1.803[.0038]
-.0047[.0052]
Weight 76.73[.507]
76.43[.421]
-0.296[.657]
Foreigner .377[.0266]
.346[.0265]
-.019[.038]
Age at the relegation season
26.05[.27]
26.05 [.29]
.005[.395]
Years of experience before
7.357576[.3688691]
7.377778[.4017467]
-.020202[.5462223]
loaned or swapped to other clubs before
.230303[.0328767]
.2666667[.0382017]
-.0363636[.0501499]
Player’s maximum transfer fee
244059.7[31947.88]
194463.5 [28311.36] 49596.27 [43469.08]
#players 340 330
Empirical Strategy
• The relegated versus non-relegated research design suggests the following specification:
Heterogeneous effect across players
• Direct implication: Younger players should “benefit more” in
long-term job placement• A Triple-Difference Strategy will not work!• Categorize the sample into two sub-groups
according to the age at relegation season
Discussing different measures (1)
• Two measures for career development Team ranking job quality Transfer fee market value• Use rank as a measure for job quality Higher ranking also means higher wage wage=basic pay + appearance money + bonuses
Measure job quality19
92-9
3
1993
-94
1994
-95
1995
-96
1996
-97
1997
-98
1998
-99
1999
-00
2000
-01
2001
-02
2002
-03
2003
-040
100,000
200,000
300,000
400,000
500,000
600,000
700,000
The basic average annual pay of England’s professional players
average worker's wagePremier LeagueFirst DivisionSecond DivisionThird Division
season
£
Average UKWorkers wage, £
Season Premier League
First Division
Second Division
Third Division
(1) (2) (3) (4) (5) (6)
£18,356 1992-93 £77,083 £40,728 £21,840 £16,640
£18,824 1993-94 £93,968 £47,358 £23,745 £17,190
£19,552 1994-95 £116,448 £51,480 £24,076 £19,760
£20,332 1995-96 £130,896 £52,000 £26,000 £21,840
£21,632 1996-97 £175,066 £56,680 £28,600 £20,540
£22,828 1997-98 £244,908 £59,280 £34,060 £24,492
£23,660 1998-99 £313,959 £62,608 £39,104 £23,244
£24,596 1999-00 £383,835 £71,500 £38,532 £25,272
£26,000 2000-01 £451,274 £94,640 £52,416 £28,704
£27,300 2001-02 £566,932 £115,700 £50,336 £28,600
£28,132 2002-03 £611,068 £90,948 £59,488 £30,056
£28,600 2003-04 £651,222 £92,300 £55,052 £42,472
The basic average annual pay of England’s professional playersSources: from internal PFA union files.
Measure market value : transfer fee
Discussing different measures (2)
• Use transfer fee as a measure for market value• Selected sample? Relegated team players: 3.03 transfers Non-relegated team players: 2.94 transfers Over 90% of the players experienced at least one transfer after season 0
• Measurement error in the dependent variable: As long as the error is not correlated with relegation assignment, it only
results in a larger error variance.
Measure the degree of practice
• Total annual appearances (including substitute appearances)
• Appearances in starting line-up
• Issue of measurementAppearances may not be able to capture the
exact minutes Intensity
Graphical presentation on the primary findings
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 81
1.5
2
2.5
3
3.5
4
4.5
Figure 4: Average League Level of Players
just relegatedjust not relegated
normalized year
Leve
l
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8
-1.5
-1
-0.5
0
0.5
1
1.5
Figure 5: Differences in League Levels of Players
normalized year
diffe
renc
e
-6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 81
1.5
2
2.5
3
3.5
4
4.5
Figure 6A: Average Level of League that Players joinedYoung Players: younger than 25 at the time of relegation
year
Just RelegatedJust Not Relegated
normalized year
Leve
l
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 81
1.5
2
2.5
3
3.5
4
4.5
Figure 6B: Average Level of League that Players joinedPlayers between 25 and 30 at the time of relegation year
Just RelegatedJust Not Relegated
normalized year
Leve
l
-8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 81
1.5
2
2.5
3
3.5
4
4.5
5
Figure 6C: Average Level of League that Players joinedPlayers older than 30 at the time of relegation year
Just RelegateJust Not Relegate
normalized year
Leve
l
Understand the mechanism
-5 -4 -3 -2 -1 0 1 2 3 4 5 69
11
13
15
17
19
21
23
25
27
Figure 7A-Annual Appearances of all players
relegate
not relegate
normalized year
year
ly A
ppea
ranc
es
-5 -4 -3 -2 -1 0 1 2 3 4 5 6
-10
-8
-6
-4
-2
0
2
4
6
8
Figure 7B-Difference in appearances for all players
normalized year
diffe
renc
e (r
eleg
ate-
non
rele
gate
)
Other outcomes
1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
Figure 8- Dropout propensity after relegation season
relegatenon relegate
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 100
0.1
0.2
0.3
0.4
0.5
0.6
Figure 9- Propensity of transferring to other clubs
relegated
non rel-egated
-16
-15
-14
-13
-12
-11
-10
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160
200000
400000
600000
800000
1000000
1200000
1400000
Figure 10-Transfer Fee
not relegatedrelegated
half-year period
poun
d
-16 -15 -14 -13 -12 -11 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
-1500000
-1000000
-500000
0
500000
1000000
1500000
Figure 11-Difference in Transfer Fee
Results of the statistical models
• Preview All results from fitting the Difference-In-
Difference regression are consistent with the graphical patterns shown using raw data
The regression results are robust to player fixed-effect and calendar-year fixed-effect
Table 3 Difference-In-Difference estimation on the effect of relegation on the ranking of the club signed up VARIABLES League Level Overall Ranking
(1) (2) (3) (4) (5) (6)Relegate*Season -4 -0.094 -0.121 -0.067 -2.150 -2.724 -1.584
(0.112) (0.109) (0.102) (2.566) (2.505) (2.306)Relegate*Season -3 -0.128 -0.164 -0.129 -3.595 -4.400* -3.692
(0.118) (0.116) (0.112) (2.688) (2.625) (2.535)Relegate*Season -2 -0.100 -0.155 -0.080 -0.158 -1.411 0.107
(0.116) (0.113) (0.114) (2.639) (2.559) (2.537)Relegate*Season -1 0.175 0.104 0.171 2.025 0.460 1.853
(0.111) (0.110) (0.112) (2.522) (2.483) (2.495)Relegate*Season 0 0.057 -0.026 0.040 0.790 -0.999 0.421
(0.106) (0.105) (0.112) (2.409) (2.385) (2.505)Relegate*Season 1 0.487*** 0.413*** 0.510*** 5.078** 3.516 5.634**
(0.111) (0.112) (0.118) (2.561) (2.552) (2.657)Relegate*Season 2 0.180 0.123 0.235* 1.288 0.106 2.404
(0.120) (0.120) (0.125) (2.803) (2.781) (2.854)Relegate*Season 3 -0.065 -0.107 0.044 -2.464 -3.360 -0.268
(0.132) (0.131) (0.135) (3.034) (3.002) (3.078)Relegate*Season 4 -0.179 -0.211 -0.067 -4.376 -5.087 -1.918
(0.148) (0.146) (0.151) (3.371) (3.337) (3.427)Relegate*Season 5 -0.235 -0.267* -0.232 -5.570 -6.266* -5.505
(0.156) (0.156) (0.160) (3.514) (3.494) (3.590)Relegate*Season 6 -0.333** -0.359** -0.303* -7.296* -7.865** -6.460*
(0.166) (0.166) (0.172) (3.732) (3.723) (3.832)Relegate*Season 7 -0.378** -0.384** -0.345** -8.498** -8.559** -7.450*
(0.172) (0.172) (0.173) (3.848) (3.831) (3.860)Relegate*Season 8 -0.437** -0.452** -0.384** -11.514*** -11.793*** -10.389**
(0.181) (0.180) (0.182) (4.060) (4.032) (4.071)Relegate*Season 9 -0.406** -0.437** -0.342* -10.321** -10.924*** -8.735*
(0.194) (0.191) (0.190) (4.287) (4.226) (4.189)Relegate*Season 10 -0.210 -0.230 -0.166 -5.261 -5.575 -4.093
(0.212) (0.208) (0.228) (4.761) (4.651) (4.503)Calendar Year F.E. No Yes. Yes No Yes. YesPlayer F.E. No No Yes No No YesSe clustered at player level Yes Yes Yes Yes Yes Yes
Observations 86401 86401 86401 86401 86401 86401R-squared 0.124 0.145 0.415 0.110 0.136 0.411
Table 4- DID estimation on the effect of relegation on the ranking of club played (Including the cases of being loaned or swapped to other clubs)
VARIABLES League level Overall ranking(1) (2) (3) (4) (5) (6)
Relegate*Season -4 -0.093 -0.118 -0.056 -2.096 -2.631 -1.352(0.108) (0.106) (0.100) (2.481) (2.431) (2.271)
Relegate*Season -3 -0.139 -0.172 -0.133 -3.909 -4.643* -3.847(0.114) (0.113) (0.110) (2.606) (2.559) (2.497)
Relegate*Season -2 -0.121 -0.173 -0.081 -0.717 -1.890 -0.015(0.112) (0.110) (0.111) (2.543) (2.482) (2.475)
Relegate*Season -1 0.116 0.048 0.122 0.615 -0.883 0.642(0.108) (0.107) (0.109) (2.438) (2.416) (2.430)
Relegate*Season 0 0.007 -0.073 0.000 -0.383 -2.117 -0.492(0.103) (0.103) (0.109) (2.354) (2.335) (2.434)
Relegate*Season 1 0.402*** 0.332*** 0.431*** 3.346 1.888 4.047(0.108) (0.109) (0.114) (2.493) (2.491) (2.563)
Relegate*Season 2 0.165 0.111 0.225* 0.963 -0.123 2.229(0.117) (0.117) (0.121) (2.728) (2.716) (2.775)
Relegate*Season 3 -0.080 -0.119 0.033 -2.908 -3.708 -0.618(0.128) (0.128) (0.131) (2.956) (2.938) (2.987)
Relegate*Season 4 -0.233 -0.262* -.210 -5.637* -6.254* -2.982(0.144) (0.143) (.153) (3.285) (3.265) (3.337)
Relegate*Season 5 -0.292* -0.322** -0.303* -6.826** -7.474** -7.014*(0.153) (0.153) (0 .164) (3.444) (3.437) (3.505)
Relegate*Season 6 -0.374** -0.399** -0.363** -8.280** -8.801** -7.822**(0.164) (0.164) (0.175) (3.671) (3.670) (3.754)
Relegate*Season 7 -0.398** -0.403** -0.381** -9.250** -9.289** -8.556**(0.171) (0.171) (0.181) (3.813) (3.802) (3.796)
Relegate*Season 8 -0.467*** -0.480*** -0.427** -12.218*** -12.446*** -11.354***(0.179) (0.179) (0.193) (4.014) (3.989) (3.997)
Relegate*Season 9 -0.449** -0.479** -0. 404* -11.293*** -11.867*** -10.114(0.191) (0.189) (0.207) (4.224) (4.161) (4.667)**
Relegate*Season 10 -0.247 -0.268 -0.221 -6.202 -6.515 -5.343(0.213) (0.209) (0.228) (4.775) (4.663) (5.220)
Player F.E. No No Yes No No YesCalendar year F.E. No Yes No No Yes NoSe clustered at player level Yes Yes Yes Yes Yes YesObservations 86401 86401 86401 86401 86401 86401R-squared 0.118 0.139 0.411 0.106 0.130 0.407
Table 5- Difference in difference estimation on turnoverVARIABLES Dropout Transfer
(1) (2) (3) (4) (5) (6)
Relegate*Season -4 0.007 0.007 0.008(0.006) (0.006) (0.006)
Relegate*Season -3 -0.011* -0.011* -0.010*(0.006) (0.006) (0.006)
Relegate*Season -2 -0.000 0.000 0.001(0.006) (0.006) (0.006)
Relegate*Season -1 -0.007 -0.007 -0.006(0.005) (0.005) (0.006)
Relegate*Season 0 0.001 0.001 0.002(0.005) (0.005) (0.006)
Relegate*Season 1 0.002 0.004 0.017 0.005 0.005 0.006(0.003) (0.006) (0.017) (0.005) (0.005) (0.005)
Relegate*Season 2 -0.005 -0.003 0.011 -0.004 -0.004 -0.003(0.014) (0.015) (0.024) (0.005) (0.005) (0.005)
Relegate*Season 3 -0.006 -0.004 0.009 0.000 0.000 0.002(0.020) (0.021) (0.028) (0.006) (0.006) (0.006)
Relegate*Season 4 0.001 0.002 0.016 -0.001 -0.001 -0.000(0.024) (0.025) (0.033) (0.006) (0.006) (0.006)
Relegate*Season 5 -0.007 -0.005 0.008 0.001 0.001 0.002(0.029) (0.030) (0.037) (0.006) (0.006) (0.006)
Relegate*Season 6 0.010 0.012 0.025 -0.001 -0.001 -0.001(0.032) (0.033) (0.039) (0.006) (0.006) (0.006)
Relegate*Season 7 0.021 0.023 0.036 0.001 0.002 0.002(0.035) (0.035) (0.040) (0.006) (0.006) (0.006)
Relegate*Season 8 0.010 0.012 0.025 -0.000 -0.000 0.001(0.036) (0.037) (0.040) (0.006) (0.006) (0.006)
Relegate*Season 9 0.020 0.021 0.035 0.011* 0.011* 0.012*(0.037) (0.037) (0.040) (0.007) (0.007) (0.007)
Relegate*Season 10 -0.018 -0.016 -0.003 0.012* 0.012* 0.014*(0.037) (0.037) (0.039) (0.007) (0.007) (0.008)
Player F.E. No No Yes No No YesCalendar year F.E. No Yes No No Yes NoSe clustered at player level Yes Yes Yes Yes Yes Yes
Observations 8965 8965 8965 86555 86,555 86,555
Transfer feeVARIABLES Transfer fee
(1) (2) (3)Relegate*Season -4 -48,407.177 -54,363.095 -295,124.153
(140,078.780) (140,172.362) (213,075.683)Relegate*Season -3 -82,677.053 -76,472.486 -265,909.875
(131,331.597) (127,038.489) (191,687.705)Relegate*Season -2 14,541.054 16,912.936 -46,487.679
(113,227.529) (111,555.667) (131,505.001)Relegate*Season -1 -37,341.910 -48,576.166 -138,731.819
(174,583.523) (172,264.787) (247,725.277)Relegate*Season 0 -59,308.761 -211.932 -147,310.248
(112,229.513) (110,831.593) (155,562.698)Relegate*Season 1 210,060.860 260,744.033 83,967.831
(184,266.562) (177,518.608) (181,085.527)Relegate*Season 2 -180,997.077 -233,821.726* -354,786.711**
(123,433.656) (127,034.759) (161,678.502)Relegate*Season 3 -59,203.310 -70,007.515 -63,641.260
(111,532.839) (113,629.212) (122,012.637)Relegate*Season 4 -111,566.301 -120,516.895 -323,435.679
(217,302.434) (215,477.001) (236,702.864)Relegate*Season 5 257,807.959 239,246.635 180,373.068
(242,884.018) (237,414.380) (228,568.433)Relegate*Season 6 146,866.165 143,371.901 142,849.853
(283,689.014) (272,994.684) (238,768.606)Relegate*Season 7 260,721.252 246,985.656 131,414.907
(242,084.795) (242,659.982) (213,617.193)Relegate*Season 8 172,471.458 190,129.559 124,178.822
(185,333.221) (177,373.157) (137,994.897)Relegate*Season 9 248,341.556 291,105.844 25,735.687
(242,833.961) (239,398.718) (186,480.490)Relegate*Season 10 384,006.926 316,833.964 112,553.754
(250,832.246) (255,371.252) (194,334.784)F.E. No Calendar year f.e. Player f.e.Se clustered at player level Yes Yes Yes
Observations 4,165 4,165 4,165R-squared 0.023 0.053 0.424
Appearances
VARIABLES Appearances(1) (2) (3)
Relegate*Season -4 1.153 1.098 1.252(2.115) (2.127) (2.167)
Relegate*Season -3 -2.817 -3.013 -2.801(2.222) (2.204) (2.250)
Relegate*Season -2 -0.626 -0.744 -0.571(2.285) (2.289) (2.333)
Relegate*Season -1 4.101* 3.863* 3.801(2.270) (2.276) (2.322)
Relegate*Season 0 2.140 1.999 1.382(2.097) (2.119) (2.217)
Relegate*Season 1 5.315** 5.046** 4.852**(2.223) (2.239) (2.338)
Relegate*Season 2 4.395* 4.132* 3.998*(2.243) (2.238) (2.398)
Relegate*Season 3 3.397 3.127 2.874(2.338) (2.334) (2.526)
Relegate*Season 4 1.718 1.576 1.923(2.344) (2.367) (2.544)
Relegate*Season 5 0.906 0.687 1.662(2.169) (2.174) (2.365)
Relegate*Season 6 0.840 0.653 0.899(2.333) (2.331) (2.492)
Relegate*Season 7 -1.369 -1.537 -1.378(2.522) (2.531) (2.703)
Relegate*Season 8 0.178 0.006 0.240(2.559) (2.561) (2.834)
Relegate*Season 9 1.252 0.886 2.469(2.521) (2.510) (2.780)
Relegate*Season 10 0.534 0.282 0.816(2.660) (2.689) (2.957)
Observations 5,402 5,402 5,402R-squared 0.027 0.039 0.218
Dropout ratetop panel <30; bottom panel>=30
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-1.5
-1
-0.5
0
0.5
1
1.5
2
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-2
-1
0
1
2
3
4
Transfer ratetop panel <30; bottom panel>=30
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-1.2
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
Ranking of the team on which one played top panel <30; bottom panel>=30
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-25
-20
-15
-10
-5
0
5
10
-4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10
-40
-20
0
20
40
60
80
100
Appearancestop panel <30; bottom panel>=30
-4 -3 -2 -1 0 1 2 3 4 5 6 7
-10
-5
0
5
10
15
-4 -3 -2 -1 0 1 2 3 4 5 6 7
-15
-10
-5
0
5
10
15
20
Concluding remarks
• A negative causal relationship between current job quality and future job quality.
• The big impact of practice or, more generally, learning-by-doing on human-capital accumulation in the specific industry of the English soccer league