Table 3. Effect of Union Status on Regular Inspection Hours per Mine-Quarter (Full Version: All Covariates)

Table 3. Effect of Union Status on Regular Inspection Hours per Mine-Quarter (Full Version: All Covariates)
Specification	Baseline (Hours Worked)	Employees	Tonnage
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	-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)
Lost-Day Injuries in Prev. Year	1.439***	1.660***	1.772***	1.955***	5.350***	5.815***
	(0.44)	(0.54)	(0.47)	(0.59)	(0.50)	(0.64)
Penalty Pts. in Prev. Year	9.883***	9.465***	10.314***	9.778***	12.899***	12.291***
	(0.53)	(0.46)	(0.59)	(0.50)	(0.56)	(0.54)
Mine Age	1.630***	1.914***	1.731***	2.051***	1.932***	2.123***
	(0.25)	(0.27)	(0.26)	(0.30)	(0.28)	(0.31)
Productivity	0.257	-0.002	0.103	-0.081	-3.673***	-4.154***
	(0.28)	(0.33)	(0.29)	(0.36)	(0.41)	(0.48)
NIOSH Longwall Dummy	-9.549		-9.432		26.641*
	(13.05)		(14.59)		(15.93)
Number of Coal Beds		10.010		11.134		29.515**
		(13.81)		(14.09)		(14.19)
Avg. Coal Bed Thickness (yds.)		6.828		3.746		9.221*
		(4.29)		(4.67)		(4.88)
Subsidiary Indicator		11.463**		11.161**		14.155***
		(4.66)		(4.82)		(4.79)
Pct. Captive Production		-0.364		-1.814		2.537
		(5.48)		(5.64)		(6.04)
Recoverable Reserves		-0.000***		-0.000***		-0.000
		(0.00)		(0.00)		(0.00)
Pct. Continuous Mining Method		0.091		0.137**		0.199***
		(0.06)		(0.07)		(0.07)
Pct. Conventional Mining Method		0.212***		0.245***		0.321***
		(0.07)		(0.07)		(0.08)
Pct. Longwall Mining Method		0.132		0.110		0.719***
		(0.20)		(0.23)		(0.23)
Pct. Shortwall Mining Method		0.156		-0.019		0.528**
		(0.29)		(0.39)		(0.22)
Constant	35.676*	14.958	11.379	1.054	136.533***	94.512***
	(18.60)	(24.51)	(19.86)	(25.48)	(17.99)	(27.97)
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	23,751	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
Regression Date/Time	12/2/11 16:45	12/2/11 16:45	12/2/11 16:45	12/2/11 16:45	12/2/11 16:45	12/2/11 16:45

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

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

-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)

(1.32)

(1.42)

(0.88)

(1.12)

Lost-Day Injuries in Prev. Year

1.439***

1.660***

1.772***

1.955***

5.350***

5.815***

(0.44)

(0.54)

(0.47)

(0.59)

(0.50)

(0.64)

Penalty Pts. in Prev. Year

9.883***

9.465***

10.314***

9.778***

12.899***

12.291***

(0.53)

(0.46)

(0.59)

(0.50)

(0.56)

(0.54)

Mine Age

1.630***

1.914***

1.731***

2.051***

1.932***

2.123***

(0.25)

(0.27)

(0.26)

(0.30)

(0.28)

(0.31)

Productivity

0.257

-0.002

0.103

-0.081

-3.673***

-4.154***

(0.28)

(0.33)

(0.29)

(0.36)

(0.41)

(0.48)

NIOSH Longwall Dummy

-9.549

-9.432

26.641*

(13.05)

(14.59)

(15.93)

Number of Coal Beds

10.010

11.134

29.515**

(13.81)

(14.09)

(14.19)

Avg. Coal Bed Thickness (yds.)

6.828

3.746

9.221*

(4.29)

(4.67)

(4.88)

Subsidiary Indicator

11.463**

11.161**

14.155***

(4.66)

(4.82)

(4.79)

Pct. Captive Production

-0.364

-1.814

2.537

(5.48)

(5.64)

(6.04)

Recoverable Reserves

-0.000***

-0.000

(0.00)

Pct. Continuous Mining Method

0.091

0.137**

0.199***

(0.06)

(0.07)

Pct. Conventional Mining Method

0.212***

0.245***

0.321***

(0.07)

(0.08)

Pct. Longwall Mining Method

0.132

0.110

0.719***

(0.20)

(0.23)

Pct. Shortwall Mining Method

0.156

-0.019

0.528**

(0.29)

(0.39)

(0.22)

Constant

35.676*

14.958

11.379

1.054

136.533***

94.512***

(18.60)

(24.51)

(19.86)

(25.48)

(17.99)

(27.97)

Subunit Dummies

Yes

Quarter Dummies

Yes

District Dummies

Yes

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

0.73

0.75

0.73

0.74

0.71

0.72

Regression Date/Time

12/2/11 16:45

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: the number of regular inspection hours per mine-quarter.