| 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 | -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) | |
| Lost-Day Injuries in Prev. Year | 0.397 | 0.785 | -0.036 | 0.114 | -0.245 | 0.056 |
| (0.64) | (0.74) | (0.61) | (0.71) | (0.62) | (0.73) | |
| Penalty Pts. in Prev. Year | 2.834*** | 1.749*** | 2.392*** | 1.476*** | 2.151*** | 1.465*** |
| (0.53) | (0.49) | (0.52) | (0.53) | (0.50) | (0.48) | |
| Mine Age | 0.138 | 0.257 | 0.141 | 0.172 | 0.095 | 0.140 |
| (0.39) | (0.49) | (0.38) | (0.48) | (0.37) | (0.47) | |
| Productivity | -1.777 | -0.853 | -0.893 | -0.499 | -0.843 | -0.787 |
| (1.11) | (1.27) | (1.03) | (1.29) | (0.85) | (1.07) | |
| NIOSH Longwall Dummy | 35.119* | 31.775 | 19.895 | |||
| (19.71) | (19.90) | (20.78) | ||||
| Number of Coal Beds | -3.271 | -0.148 | 2.081 | |||
| (24.04) | (24.32) | (24.31) | ||||
| Avg. Coal Bed Thickness (yds.) | -2.955 | 0.008 | 0.137 | |||
| (8.83) | (8.45) | (8.39) | ||||
| Subsidiary Indicator | 6.095 | 13.569 | 14.558 | |||
| (10.97) | (10.89) | (10.66) | ||||
| Pct. Captive Production | 17.909 | 19.168 | 18.492 | |||
| (20.41) | (20.97) | (21.23) | ||||
| Recoverable Reserves | -0.000 | -0.000 | -0.000 | |||
| (0.00) | (0.00) | (0.00) | ||||
| Pct. Continuous Mining Method | -0.233 | -0.071 | -0.004 | |||
| (0.15) | (0.13) | (0.13) | ||||
| Pct. Conventional Mining Method | -0.100 | 0.057 | 0.110 | |||
| (0.16) | (0.15) | (0.15) | ||||
| Pct. Longwall Mining Method | -0.221 | -0.055 | -0.125 | |||
| (0.37) | (0.39) | (0.40) | ||||
| Pct. Shortwall Mining Method | -0.396 | -0.178 | -0.096 | |||
| (1.15) | (1.17) | (1.19) | ||||
| Constant | 61.483*** | 164.952*** | 116.283*** | 102.028*** | 109.349*** | 94.458** |
| (18.16) | (37.81) | (20.54) | (38.10) | (19.23) | (38.60) | |
| 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 | 23,273 | 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 |
| Regression Date/Time | 12/2/11 16:53 | 12/2/11 16:53 | 12/2/11 16:53 | 12/2/11 16:53 | 12/2/11 16:53 | 12/2/11 16:53 |
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 Violations per 1000 Onsite Inspection Hours per mine-quarter.