Table 5. Effect of Union Status on Total Violations per Mine-Quarter (Full Version: All Covariates)
Specification	Baseline (Hours Worked)	Employees	Tonnage
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)
Lost-Day Injuries in Prev. Year	0.632***	0.594***	0.645***	0.611***	1.035***	1.025***
	(0.23)	(0.22)	(0.22)	(0.22)	(0.23)	(0.21)
Penalty Pts. in Prev. Year	2.455***	2.236***	2.473***	2.253***	2.744***	2.501***
	(0.12)	(0.14)	(0.13)	(0.15)	(0.10)	(0.14)
Mine Age	0.248***	0.295***	0.260***	0.309***	0.284***	0.315***
	(0.08)	(0.09)	(0.08)	(0.09)	(0.07)	(0.08)
Productivity	-0.291***	-0.267***	-0.296***	-0.284***	-0.553***	-0.619***
	(0.06)	(0.09)	(0.06)	(0.09)	(0.07)	(0.09)
NIOSH Longwall Dummy	4.290		3.724		9.025***
	(3.65)		(3.80)		(3.50)
Number of Coal Beds		2.017		2.091		4.137
		(3.32)		(3.33)		(3.25)
Avg. Coal Bed Thickness (yds.)		0.783		0.568		1.205
		(1.40)		(1.45)		(1.45)
Subsidiary Indicator		-0.640		-0.508		0.362
		(1.06)		(1.16)		(1.12)
Pct. Captive Production		-1.768*		-2.004*		-1.809*
		(1.02)		(1.08)		(1.03)
Recoverable Reserves		0.000		0.000		0.000***
		(0.00)		(0.00)		(0.00)
Pct. Continuous Mining Method		0.021*		0.032***		0.039***
		(0.01)		(0.01)		(0.01)
Pct. Conventional Mining Method		0.027**		0.035***		0.043***
		(0.01)		(0.01)		(0.01)
Pct. Longwall Mining Method		0.005		0.009		0.083
		(0.06)		(0.06)		(0.06)
Pct. Shortwall Mining Method		0.545		0.533		0.598
		(0.41)		(0.40)		(0.43)
Constant	8.419**	4.875	21.087***	7.248	29.067***	12.695**
	(3.94)	(7.38)	(3.59)	(6.44)	(3.52)	(6.29)
Subunit Dummies	Yes	Yes	Yes	Yes	Yes	Yes
Quarter Dummies	Yes	Yes	Yes	Yes	Yes	Yes
District Dummies	Yes	Yes	Yes	Yes	Yes	Yes
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
Regression Date/Time	12/2/11 16:46	12/2/11 16:46	12/2/11 16:46	12/2/11 16:46	12/2/11 16:47	12/2/11 16:47

Table 5. Effect of Union Status on Total Violations per Mine-Quarter (Full Version: All Covariates)

Specification

Baseline (Hours Worked)

Employees

Tonnage

Model

Public Fields Only

Confidential Fields

Public Fields Only

Confidential Fields

Public Fields Only

Confidential Fields

Mine/Controller Size Units:

100 Quarterly FTEs

100 Employees

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)

Lost-Day Injuries in Prev. Year

0.632***

0.594***

0.645***

0.611***

1.035***

1.025***

(0.23)

(0.22)

(0.23)

(0.21)

Penalty Pts. in Prev. Year

2.455***

2.236***

2.473***

2.253***

2.744***

2.501***

(0.12)

(0.14)

(0.13)

(0.15)

(0.10)

(0.14)

Mine Age

0.248***

0.295***

0.260***

0.309***

0.284***

0.315***

(0.08)

(0.09)

(0.08)

(0.09)

(0.07)

(0.08)

Productivity

-0.291***

-0.267***

-0.296***

-0.284***

-0.553***

-0.619***

(0.06)

(0.09)

(0.06)

(0.09)

(0.07)

(0.09)

NIOSH Longwall Dummy

4.290

3.724

9.025***

(3.65)

(3.80)

(3.50)

Number of Coal Beds

2.017

2.091

4.137

(3.32)

(3.33)

(3.25)

Avg. Coal Bed Thickness (yds.)

0.783

0.568

1.205

(1.40)

(1.45)

Subsidiary Indicator

-0.640

-0.508

0.362

(1.06)

(1.16)

(1.12)

Pct. Captive Production

-1.768*

-2.004*

-1.809*

(1.02)

(1.08)

(1.03)

Recoverable Reserves

0.000

0.000***

(0.00)

Pct. Continuous Mining Method

0.021*

0.032***

0.039***

(0.01)

Pct. Conventional Mining Method

0.027**

0.035***

0.043***

(0.01)

Pct. Longwall Mining Method

0.005

0.009

0.083

(0.06)

Pct. Shortwall Mining Method

0.545

0.533

0.598

(0.41)

(0.40)

(0.43)

Constant

8.419**

4.875

21.087***

7.248

29.067***

12.695**

(3.94)

(7.38)

(3.59)

(6.44)

(3.52)

(6.29)

Subunit Dummies

Yes

Quarter Dummies

Yes

District Dummies

Yes

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

0.62

0.64

0.62

0.64

0.61

0.63

Regression Date/Time

12/2/11 16:46

12/2/11 16:47

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

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: public sample is: (1==1) (underground_mine==1) (coal_dummy==1) (bituminous==1) (active==1) (first_qtr_of_production==0) inrange(year, 1995, 2009). private sample is: (1==1) (underground_mine==1) (coal_dummy==1) (bituminous==1) (active==1) (first_qtr_of_production==0) inrange(year, 1998, 2009).

Independent Variables: All models include the following regressors: union dummy, union-size interaction term, mine size measure (defined as specified in column headers), logged controller size measure (defined as specified in column headers), mine age, productivity, number of lost-work injuries (in hundreds) in the previous four quarters, total penalty points (in thousands) in the previous four quarters, a constant term, dummies indicating presence of each type of mine subunit, quarter dummies, and district dummies. In addition: "Public Fields Only" models include the NIOSH longwall dummy; and "Confidential Fields" 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.

Dependent Variable: total number of violations per mine-quarter.