Table 4. Effect of Union Status on Proportion of All Inspection Hours Spent Onsite per Regular Inspection (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 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)
Lost-Day Injuries in Prev. Year 0.000 0.000 0.000 0.000 0.001*** 0.001**
(0.00) (0.00) (0.00) (0.00) (0.00) (0.00)
Penalty Pts. in Prev. Year 0.000 0.001** 0.000* 0.001*** 0.001*** 0.001***
(0.00) (0.00) (0.00) (0.00) (0.00) (0.00)
Mine Age -0.000 -0.000 -0.000 -0.000 -0.000 0.000
(0.00) (0.00) (0.00) (0.00) (0.00) (0.00)
Productivity -0.000 -0.000 -0.001* -0.000 -0.001*** -0.001**
(0.00) (0.00) (0.00) (0.00) (0.00) (0.00)
NIOSH Longwall Dummy -0.006   -0.004   0.005  
(0.01)   (0.01)   (0.01)  
Number of Coal Beds   0.001   0.002   0.003
  (0.01)   (0.01)   (0.01)
Avg. Coal Bed Thickness (yds.)   0.000   0.001   0.001
  (0.00)   (0.00)   (0.00)
Subsidiary Indicator   -0.016***   -0.018***   -0.020***
  (0.00)   (0.01)   (0.00)
Pct. Captive Production   0.005   0.005   0.006
  (0.01)   (0.01)   (0.01)
Recoverable Reserves   -0.000   -0.000   -0.000
  (0.00)   (0.00)   (0.00)
Pct. Continuous Mining Method   0.000***   0.000***   0.000***
  (0.00)   (0.00)   (0.00)
Pct. Conventional Mining Method   0.001***   0.001***   0.001***
  (0.00)   (0.00)   (0.00)
Pct. Longwall Mining Method   0.000**   0.000**   0.000**
  (0.00)   (0.00)   (0.00)
Pct. Shortwall Mining Method   0.000   0.000   0.000
  (0.00)   (0.00)   (0.00)
Constant 0.380** 0.609*** 0.610*** 0.142*** 0.631*** 0.586***
(0.16) (0.02) (0.01) (0.02) (0.01) (0.02)
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 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
Regression Date/Time 12/3/11 00:09 12/3/11 00:09 12/3/11 00:09 12/3/11 00:09 12/3/11 00:09 12/3/11 00:09

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 regular inspection.

Sample: public sample is: (regular_inspection==1) (underground_mine==1) (coal_dummy==1) (bituminous==1) (active==1) (first_qtr_of_production==0) inrange(year, 1995, 2009). private sample is: (regular_inspection==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 proportion of all inspection hours that are spent onsite per regular inspection.