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• Alison Morantz, Does Unionization Strengthen Regulatory Enforcement? An Empirical Study of the Mine Safety and Health Administration, 14 J. Legis. & Pub. Pol'y 697 (2011).
• Note on data availability: the data used in this paper was obtained from government agencies including Mine Safety and Health Administration (MSHA), Energy Information Administration (EIA), and National Institute for Occupational Safety and Health (NIOSH). The mine union status data, which is critical to the paper, was provided by EIA. Unfortunately, EIA does not allow the author to distribute this data to third parties, which makes sharing the data and programs for replication impossible. If you would like to obtain the data used for this paper, please contact Joseph Conklin at joseph dot conklin at eia dot gov if the date is before August 30, 2013, or Jacob Bournazian at jacob dot bournazian at eia dot gov after August 30, 2013.
• [Abstract +-]
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• Although the United Mine Workers of America (UMWA) has always advocated strongly for miners’ safety, prior empirical literature contains no evidence that unionization reduced mine injuries or fatalities during the 1970s and ‘80s. This study uses a more comprehensive dataset and updated methodology to examine the relationship between unionization and underground, bituminous coal mine safety from 1993 to 2010. I find that unionization predicts a substantial and significant decline in traumatic mining injuries and fatalities, the two measures that I argue are the least prone to reporting bias. These disparities are especially pronounced among larger mines. My best estimates imply that overall, unionization predicts a 13-31% drop in traumatic injuries and a 27-83% drop in fatalities. Yet unionization was also associated with higher total and nontraumatic injuries during this period, suggesting that injury reporting practices differ substantially between union and nonunion mines.

Tables and Figures from Published Paper

Note: Published versions only report coefficients for variables of interest. "Expanded" tables report coefficients for all covariates except for certain dummy variables (e.g. quarter dummies). "Comprehensive" tables report all coefficients for all covariates.

• Descriptive Statistics
• [Table 1 (Published Version) +-]

• Table 1. Descriptive Statistics1

  Variable	Union Mines	Nonunion Mines	All Mines
  Number of Mines	269	1,954	2,100
  Number of Mine-Quarters	4,460	26,428	30,888
  Mean Hours Worked per Qtr.	102,336 (105,574)	30,488 (44,303)	40,863 (62,659)
  Mean Employees2 per Qtr.	184.23 (184.04)	53.67 (74.47)	75.52 (108.36)
  Mean Coal Tonnage3 per Qtr.	403,320 (483,518)	132,198 (280,797)	171,346 (332,106)

  1 Standard deviations, where applicable, are reported in parentheses. Mines that were unionized for some but not all of the quarters in which they were active are included in both the union and non-union mine counts; therefore, the sum of union and non-union mines is greater than the value of all mines.

  2 See Mine Safety & Health Admin., U.S. Dep’t Of Labor, Report On 30 C.F.R. Part 50, at 14 (1986), available at http://www.msha.gov/stats/part50/rptonpart50.pdf (defining employees as the average number of persons working during a given quarter, rounded to the nearest whole number).

  3 Tonnage is the total coal production of all sections (including surface operations) at an underground mine.

• Effect of Union Status on Regular Inspection Hours Per Mine-Quarter
• [Table 2 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 2. Effect of Union Status on Regular Inspection Hours per Mine-Quarter

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	24.089***	28.335***	19.284**	22.794**	18.346***	18.893**
  	(7.00)	(8.64)	(7.68)	(9.37)	(6.04)	(7.56)
  Union X Mine Size	-20.991***	-27.578***	-24.827***	-32.700***	-39.289*	-46.851**
  	(7.39)	(7.02)	(9.26)	(8.93)	(21.30)	(23.40)
  Mine Size	95.021***	104.234***	105.830***	120.333***	179.759***	173.459***
  	(7.86)	(7.82)	(9.84)	(10.32)	(23.65)	(24.81)
  Log of Controller Size	3.341***	2.656**	4.968***	3.998***	8.887***	8.461***
  	(1.08)	(1.08)	(1.32)	(1.42)	(0.88)	(1.12)
  Observations	23,751	17,017	23,044	16,526	23,044	16,526
  # of Union Mines / # of Total Mines	228 / 1,531	152 / 1,124	228 / 1,524	152 / 1,118	228 / 1,524	152 / 1,118
  R2	0.73	0.75	0.73	0.74	0.71	0.72

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Number of regular inspection hours per mine-quarter.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the mine-quarter.

  Sample: The sample consists of underground bituminous coal mines with positive coal production and positive hours worked. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Total Inspection Hours per Regular Inspection
• [Table 3 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 3. Effect of Union Status on Regular Inspection Hours per Mine-Quarter

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	26.118***	30.248***	22.138***	25.686***	15.809***	16.070**
  	(6.96)	(8.88)	(7.56)	(9.73)	(6.06)	(7.80)
  Union X Mine Size	-22.007***	-28.176***	-26.452***	-33.743***	-30.000*	-33.625*
  	(6.39)	(6.19)	(7.95)	(8.12)	(16.81)	(19.59)
  Mine Size	93.538***	102.464***	106.040***	119.382***	180.862***	171.963***
  	(7.10)	(7.27)	(9.03)	(10.03)	(18.47)	(19.74)
  Log of Controller Size	3.267***	2.415**	4.600***	3.686**	8.894***	8.861***
  	(1.10)	(1.22)	(1.33)	(1.63)	(0.92)	(1.16)
  Observations	21,789	14,926	21,153	14,489	21,153	14,489
  # of Union Mines / # of Total Mines	222 / 1,363	147 / 950	222 / 1,360	147 / 948	222 / 1,360	147 / 948
  R2	0.80	0.81	0.79	0.81	0.77	0.78

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Total number of inspection hours per regular inspection.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the regular inspection.

  Sample: The sample consists of regular inspections that occurred at underground bituminous coal mines with positive coal production and positive hours worked. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Proportion of All Inspection Hours Spent Onsite per Regular Inspection
• [Table 4 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 4. Effect of Union Status on Proportion of All Inspection Hours Spent Onsite per Regular Inspection

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	0.020***	0.024***	0.018***	0.021***	0.013**	0.017**
  	(0.01)	(0.01)	(0.01)	(0.01)	(0.01)	(0.01)
  Union X Mine Size	-0.005	-0.005*	-0.005	-0.005	-0.001	-0.004
  	(0.00)	(0.00)	(0.00)	(0.00)	(0.01)	(0.01)
  Mine Size	0.012***	0.013***	0.012***	0.013***	0.006	0.011
  	(0.00)	(0.00)	(0.00)	(0.00)	(0.01)	(0.01)
  Log of Controller Size	0.003***	0.004***	0.004***	0.005***	0.005***	0.006***
  	(0.00)	(0.00)	(0.00)	(0.00)	(0.00)	(0.00)
  Observations	21,789	14,926	21,153	14,489	21,153	14,489
  # of Union Mines / # of Total Mines	222 / 1,363	147 / 950	222 / 1,360	147 / 948	222 / 1,360	147 / 948
  R2	0.13	0.12	0.13	0.13	0.13	0.13

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Proportion of all inspection hours that are spent onsite per regular inspection.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the regular inspection.

  Sample: The sample consists of regular inspections that occurred at underground bituminous coal mines with positive coal production and positive hours worked. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Total Violations per Mine-Quarter
• [Table 5 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 5. Effect of Union Status on Total Violations per Mine-Quarter

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	1.310	1.996	0.805	1.400	-0.373	-0.663
  	(1.50)	(2.08)	(1.57)	(2.18)	(1.45)	(1.91)
  Union X Mine Size	-1.094	-1.638	-1.366	-2.066	3.120	3.655
  	(1.35)	(1.65)	(1.55)	(1.92)	(5.57)	(6.40)
  Mine Size	8.261***	9.664***	9.597***	11.303***	11.029***	12.190***
  	(1.20)	(1.46)	(1.34)	(1.80)	(2.90)	(3.25)
  Log of Controller Size	0.497***	0.670**	0.572**	0.771**	0.882***	0.978***
  	(0.19)	(0.29)	(0.23)	(0.36)	(0.19)	(0.29)
  Observations	23,380	16,790	22,704	16,324	22,704	16,324
  # of Union Mines / # of Total Mines	227 / 1,519	151 / 1,114	227 / 1,514	151 / 1,109	227 / 1,514	151 / 1,109
  R2	0.62	0.64	0.62	0.64	0.61	0.63

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Total violations per mine-quarter.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the mine-quarter.

  Sample: The sample consists of underground bituminous coal mines with positive coal production and positive hours worked. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Total Violations per 1000 Onsite Inspection Hours per Mine-Quarter
• [Table 6 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 6. Effect of Union Status on Total Violations per 1000 Onsite Inspection Hours per Mine-Quarter

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	-31.363***	-26.716**	-21.789**	-23.297**	-17.609**	-17.683
  	(10.40)	(11.28)	(8.49)	(10.93)	(8.76)	(11.33)
  Union X Mine Size	9.307**	7.315	7.081	6.324	19.759	16.175
  	(4.63)	(5.24)	(5.67)	(7.42)	(26.08)	(31.75)
  Mine Size	-12.422**	-5.180	-4.407	1.526	13.967	27.636
  	(5.62)	(6.15)	(6.46)	(8.60)	(22.66)	(27.66)
  Log of Controller Size	-1.915	-2.581	-6.278***	-6.789**	-6.843***	-6.885***
  	(2.21)	(2.44)	(1.81)	(2.70)	(1.61)	(2.33)
  Observations	23,273	16,694	22,601	16,230	22,601	16,230
  # of Union Mines / # of Total Mines	227 / 1,519	151 / 1,114	227 / 1,514	151 / 1,109	227 / 1,514	151 / 1,109
  R2	0.023	0.028	0.029	0.030	0.030	0.031

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Total Violations per 1000 Onsite Inspection Hours per mine-quarter.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the level. The unit of analysis for all models is the mine-quarter.

  Sample: The sample consists of underground bituminous coal mines with positive coal production and positive hours worked. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Log of Total Proposed Penalties per Mine-Quarter
• [Table 7 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 7. Effect of Union Status on Log of Total Proposed Penalties per Mine-Quarter

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	0.228***	0.240**	0.184**	0.207**	0.135*	0.090
  	(0.08)	(0.10)	(0.09)	(0.10)	(0.07)	(0.09)
  Union X Mine Size	-0.113*	-0.170***	-0.119	-0.196***	-0.180	-0.242*
  	(0.07)	(0.05)	(0.08)	(0.06)	(0.15)	(0.13)
  Mine Size	0.301***	0.378***	0.326***	0.435***	0.495***	0.624***
  	(0.05)	(0.06)	(0.07)	(0.07)	(0.12)	(0.16)
  Log of Controller Size	0.111***	0.102***	0.134***	0.123***	0.123***	0.112***
  	(0.01)	(0.02)	(0.02)	(0.02)	(0.01)	(0.02)
  Observations	23,349	16,767	22,679	16,305	22,679	16,305
  # of Union Mines / # of Total Mines	227 / 1,517	151 / 1,113	227 / 1,512	151 / 1,108	227 / 1,512	151 / 1,108
  R2	0.53	0.56	0.54	0.56	0.53	0.55

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Log of total proposed penalties per mine-quarter.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the mine-quarter.

  Sample: The sample consists of underground bituminous coal mines with positive coal production and positive hours worked. The Public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Total Penalty Points per S&S Violation — Ten Most Common Violation Types
• [Table 8 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 8. Effect of Union Status on Penalty Points per S&S Violation

  10 Most Common Violation Types

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	2.112***	2.014***	1.991***	2.012**	1.121	1.112
  	(0.73)	(0.75)	(0.75)	(0.79)	(0.70)	(0.74)
  Union X Mine Size	-0.385	-0.396*	-0.427	-0.433	-0.315	-0.339
  	(0.25)	(0.22)	(0.28)	(0.28)	(0.66)	(0.61)
  Mine Size	0.173	0.297	-0.144	0.076	0.495	0.462
  	(0.29)	(0.35)	(0.33)	(0.43)	(0.63)	(0.73)
  Log of Controller Size	1.140***	0.881***	1.341***	1.061***	1.120***	0.939***
  	(0.13)	(0.13)	(0.14)	(0.15)	(0.11)	(0.11)
  Observations	106,483	83,968	104,030	82,081	104,030	82,081
  # of Union Mines / # of Total Mines	226 / 1,547	150 / 1,134	225 / 1,540	150 / 1,129	225 / 1,540	150 / 1,129
  R2	0.81	0.84	0.81	0.84	0.81	0.84

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Total number of penalty points per S&S violation (limited to the ten most common violation types).

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, district dummies, and dummies for each violation type (i.e., section of CFR deemed to have been violated). Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the S&S violation – ten most common violation types.

  Sample: The sample consists of S&S violations received by underground bituminous coal mines with positive coal production and positive hours worked, but is restricted to the ten most common violation types. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Persons Potentially Affected Penalty Points per S&S Violation — Ten Most Common Violation Types
• [Table 9 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 9. Effect of Union Status on Persons Affected Penalty Points per S&S Violation

  10 Most Common Violation Types

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	0.182**	0.274**	0.240**	0.360***	0.114	0.219**
  	(0.09)	(0.11)	(0.10)	(0.12)	(0.09)	(0.11)
  Union X Mine Size	-0.028	-0.030	-0.056*	-0.065**	-0.007	-0.044
  	(0.02)	(0.02)	(0.03)	(0.03)	(0.07)	(0.08)
  Mine Size	0.010	-0.016	0.018	-0.003	-0.036	-0.126
  	(0.03)	(0.03)	(0.03)	(0.04)	(0.07)	(0.08)
  Log of Controller Size	-0.038***	-0.045***	-0.040***	-0.051***	-0.028**	-0.035**
  	(0.01)	(0.02)	(0.01)	(0.02)	(0.01)	(0.01)
  Observations	106,483	83,968	104,030	82,081	104,030	82,081
  # of Union Mines / # of Total Mines	226 / 1,547	150 / 1,134	225 / 1,540	150 / 1,129	225 / 1,540	150 / 1,129
  R2	0.12	0.12	0.12	0.12	0.12	0.12

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Number of penalty points assigned due to the number of persons that could be affected per S&S violation (limited to the ten most common violation types).

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, district dummies, and dummies for each violation type (i.e., section of CFR deemed to have been violated). Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the S&S violation—ten most common violation types.

  Sample: The sample consists of S&S violations received by underground bituminous coal mines with positive coal production and positive hours worked, but is restricted to the ten most common violation types. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Effect of Union Status on Mine Size Penalty Points per S&S Violation — Ten Most Common Violation Types
• [Table 10 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 10. Effect of Union Status on Mine Size Penalty Points per S&S Violation

  10 Most Common Violation Types

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	1.263***	1.287***	1.155***	1.202***	0.844***	0.753***
  	(0.26)	(0.29)	(0.27)	(0.28)	(0.22)	(0.25)
  Union X Mine Size	-0.327**	-0.380***	-0.361**	-0.432***	-0.901***	-0.878***
  	(0.14)	(0.11)	(0.16)	(0.12)	(0.35)	(0.30)
  Mine Size	0.516***	0.602***	0.505***	0.658***	0.863***	0.771**
  	(0.13)	(0.13)	(0.16)	(0.15)	(0.33)	(0.34)
  Log of Controller Size	0.503***	0.381***	0.563***	0.424***	0.516***	0.416***
  	(0.04)	(0.04)	(0.05)	(0.05)	(0.04)	(0.04)
  Observations	106,483	83,968	104,030	82,081	104,030	82,081
  # of Union Mines / # of Total Mines	226 / 1,547	150 / 1,134	225 / 1,540	150 / 1,129	225 / 1,540	150 / 1,129
  R2	0.70	0.73	0.70	0.72	0.70	0.72

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Number of penalty points assigned due to mine size per S&S violation (limited to the ten most common violation types).

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, district dummies, and dummies for each violation type (i.e., section of CFR deemed to have been violated). Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the S&S violation—ten most common violation types.

  Sample: The sample consists of S&S violations received by underground bituminous coal mines with positive coal production and positive hours worked, but is restricted to the ten most common violation types. The public-fields version models contain mine quarters from 1995–2009, whereas the confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

• Mine Size Distributions
• [Figure 1 (Published Version) +-]

• Figure 1a: Total Hours Workeda
  Figure 1b: Employeesa
  Figure 1c: Tonnagea

  a. The horizontal axis represents the log of the size measure. Therefore the density plots are in fact density plots of the log of the size measure.

• Effect of Union Status on Total Abatement Period per S&S Violation — Ten Most Common Violation Types
• [Table 11 (Published Version) +-]
• [Expanded Version: view  |  download ]
• [Comprehensive Version: view  |  download ]

• Table 11. Effect of Union Status on Actual Abatement Period per S&S Violation

  10 Most Common Violation Types

  Specification	Baseline (Hours Worked)		Employees		Tonnage
  Model	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version	Public-Fields Version	Confid.-Fields Version
  Mine/Controller Size Units:	100 Quarterly FTEs	100 Quarterly FTEs	100 Employees	100 Employees	Millions of Tons	Millions of Tons
  Union	0.333	-0.044	0.407	-0.030	-0.024	-0.407
  	(0.67)	(0.47)	(0.69)	(0.48)	(0.58)	(0.41)
  Union X Mine Size	-0.201	-0.084	-0.251	-0.109	-0.326	0.053
  	(0.14)	(0.12)	(0.17)	(0.15)	(0.43)	(0.29)
  Mine Size	-0.132	-0.173	-0.078	-0.109	-0.405	-0.945**
  	(0.13)	(0.13)	(0.16)	(0.17)	(0.44)	(0.42)
  Log of Controller Size	-0.101	-0.131	-0.140*	-0.239***	-0.118*	-0.183***
  	(0.08)	(0.10)	(0.08)	(0.08)	(0.07)	(0.07)
  Observations	110,128	86,745	107,424	84,706	107,424	84,706
  # of Union Mines / # of Total Mines	226 / 1,548	150 / 1,134	225 / 1,540	150 / 1,129	225 / 1,540	150 / 1,129
  R2	0.020	0.027	0.021	0.030	0.021	0.030

  Source: MSHA, EIA and NIOSH, 1995–2009.

  Definitions: Significance levels: *** 1%, ** 5%, * 10%. FTE is defined as 2,000 man-hours.

  Dependent Variable: Total abatement period per S&S violation (limited to the ten most common violation types), defined as the termination date minus the issue date.

  Independent Variables: All models include the following regressors: union dummy, union X size, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, total lost-work injuries (in hundreds) in previous four quarters, total penalty points (in thousands) in previous four quarters, constant term, dummies indicating presence of each type of mine subunit, quarter dummies, district dummies, and dummies for each violation type (i.e., section of CFR deemed to have been violated). Public-fields version models include a longwall indicator. Confidential-fields version models include number of coal beds, mean coal bed thickness (in yards), subsidiary indicator, captive production as a percentage of total production, recoverable coal reserves, and mining method percentages. See infra Appendix B for full definitions of all variables.

  Models: All models are ordinary least squares regressions; standard errors (shown in parentheses) are clustered at the mine level. The unit of analysis for all models is the S&S violation—ten most common violation types.

  Sample: The sample consists of S&S violations received by underground bituminous coal mines with positive coal production and positive hours worked, but is restricted to the ten most common violation types. The public-fields version models contain mine quarters from 1995–2009, whereas the Confidential-fields version models are restricted to 1998–2009. All specifications exclude mine-quarters in which a mine began production for the first time or resumed production after a year or more of inactivity.

Supplementary Materials