| 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) | ||||
| Augur Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Culm/Refuse Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Dredge Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Ind. Shop/Yard Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Mill/Prep. Plant Subunit Dummy | 7.783 | 9.916 | 6.314 | 10.326 | 2.777 | 8.094 |
| (17.30) | (21.79) | (16.39) | (20.69) | (15.38) | (19.58) | |
| Other Mining Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Strip/Quarry/Pit Subunit Dummy | (dropped) | (dropped) | -64.448*** | (dropped) | -66.256*** | (dropped) |
| (10.00) | (10.01) | |||||
| Surface at Underground Subunit | 1.098 | 5.809 | -0.396 | 7.244 | -0.458 | 6.866 |
| Dummy | (7.00) | (6.52) | (6.43) | (6.55) | (6.42) | (6.54) |
| Underground Subunit Dummy | 62.527*** | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| (10.42) | ||||||
| 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) | ||||
| MSHA Coal District 1 Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| MSHA Coal District 2 Dummy | -32.511* | -56.436*** | -27.901 | -24.515 | -35.130** | -36.442* |
| (16.98) | (21.43) | (17.49) | (21.27) | (17.20) | (20.64) | |
| MSHA Coal District 3 Dummy | 38.623** | 21.815 | 41.040** | 48.320** | 33.155* | 36.417* |
| (17.56) | (20.59) | (17.83) | (20.89) | (17.07) | (20.00) | |
| MSHA Coal District 4 Dummy | 57.821*** | 45.107** | 66.191*** | 78.619*** | 61.523*** | 68.115*** |
| (17.82) | (20.21) | (18.14) | (21.42) | (16.53) | (19.76) | |
| MSHA Coal District 5 Dummy | -5.611 | -19.489 | 0.245 | 9.243 | -7.824 | -4.233 |
| (15.85) | (18.98) | (16.10) | (18.99) | (14.43) | (17.05) | |
| MSHA Coal District 6 Dummy | 45.285*** | 9.207 | 50.486*** | 37.364* | 43.596*** | 24.806 |
| (17.37) | (19.28) | (17.61) | (19.85) | (15.96) | (17.57) | |
| MSHA Coal District 7 Dummy | 39.222** | 19.728 | 43.280** | 49.213** | 35.589** | 36.299** |
| (17.14) | (19.72) | (17.26) | (19.39) | (15.56) | (16.86) | |
| MSHA Coal District 8 Dummy | 30.807 | 7.829 | 32.383 | 35.608 | 23.800 | 24.898 |
| (24.46) | (24.35) | (25.93) | (31.71) | (25.36) | (31.60) | |
| MSHA Coal District 9 Dummy | 118.870*** | 114.423*** | 112.882*** | 125.658*** | 105.420*** | 112.888*** |
| (27.16) | (37.16) | (24.95) | (32.19) | (23.52) | (30.66) | |
| MSHA Coal District 10 Dummy | 24.697 | (dropped) | 26.741 | 27.901 | 16.374 | 12.156 |
| (19.08) | (20.40) | (26.68) | (21.19) | (28.26) | ||
| MSHA Coal District 11 Dummy | (dropped) | -24.571 | (dropped) | (dropped) | (dropped) | (dropped) |
| (25.12) | ||||||
| MSHA Coal District 12 Dummy | 71.422*** | 33.596 | 66.281*** | 65.456*** | 58.658*** | 52.711*** |
| (20.17) | (21.37) | (18.33) | (20.76) | (16.68) | (18.56) | |
| Quarter Dummy - 1993q1 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1993q2 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1993q3 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1993q4 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1994q1 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1994q2 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1994q3 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1994q4 | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Quarter Dummy - 1995q1 | 46.611*** | (dropped) | 40.052*** | (dropped) | 39.106*** | (dropped) |
| (11.77) | (9.40) | (9.28) | ||||
| Quarter Dummy - 1995q2 | 53.975*** | (dropped) | 48.254*** | (dropped) | 47.574*** | (dropped) |
| (11.95) | (9.53) | (9.45) | ||||
| Quarter Dummy - 1995q3 | 44.667*** | (dropped) | 41.494*** | (dropped) | 40.835*** | (dropped) |
| (11.43) | (9.30) | (9.22) | ||||
| Quarter Dummy - 1995q4 | 75.899*** | (dropped) | 72.919*** | (dropped) | 72.242*** | (dropped) |
| (21.31) | (20.50) | (20.49) | ||||
| Quarter Dummy - 1996q1 | 15.328 | (dropped) | 6.967 | (dropped) | 6.278 | (dropped) |
| (11.36) | (8.24) | (8.17) | ||||
| Quarter Dummy - 1996q2 | 83.444 | (dropped) | 29.010* | (dropped) | 28.357* | (dropped) |
| (54.64) | (15.17) | (15.11) | ||||
| Quarter Dummy - 1996q3 | 31.665*** | (dropped) | 22.221*** | (dropped) | 21.351** | (dropped) |
| (11.89) | (8.47) | (8.37) | ||||
| Quarter Dummy - 1996q4 | 26.385** | (dropped) | 22.727** | (dropped) | 22.179** | (dropped) |
| (11.49) | (8.83) | (8.73) | ||||
| Quarter Dummy - 1997q1 | 23.943** | (dropped) | 12.612 | (dropped) | 12.005 | (dropped) |
| (11.93) | (8.75) | (8.66) | ||||
| Quarter Dummy - 1997q2 | 33.495** | (dropped) | 27.105** | (dropped) | 26.601** | (dropped) |
| (13.24) | (10.79) | (10.77) | ||||
| Quarter Dummy - 1997q3 | 38.613** | (dropped) | 34.198** | (dropped) | 33.533** | (dropped) |
| (16.50) | (14.75) | (14.69) | ||||
| Quarter Dummy - 1997q4 | 42.285* | (dropped) | 38.185* | (dropped) | 37.581* | (dropped) |
| (22.07) | (20.72) | (20.71) | ||||
| Quarter Dummy - 1998q1 | 14.508 | 3.513 | 10.484 | 11.649 | 9.792 | 11.442 |
| (11.64) | (14.21) | (8.61) | (13.70) | (8.58) | (13.51) | |
| Quarter Dummy - 1998q2 | 14.201 | 4.350 | 8.678 | 10.611 | 7.854 | 10.234 |
| (11.89) | (14.68) | (9.06) | (14.19) | (9.01) | (13.97) | |
| Quarter Dummy - 1998q3 | 15.127 | 3.793 | 8.808 | 8.973 | 8.225 | 8.913 |
| (11.45) | (13.97) | (8.20) | (13.46) | (8.13) | (13.25) | |
| Quarter Dummy - 1998q4 | 41.125*** | 30.358* | 35.766*** | 36.812** | 35.500*** | 36.879** |
| (14.69) | (15.60) | (11.86) | (14.84) | (11.83) | (14.65) | |
| Quarter Dummy - 1999q1 | 71.574 | 65.905 | 69.905 | 72.751 | 69.662 | 72.583 |
| (48.53) | (49.43) | (50.90) | (51.13) | (50.90) | (51.14) | |
| Quarter Dummy - 1999q2 | 8.909 | 4.114 | 2.651 | 6.264 | 2.687 | 6.320 |
| (14.77) | (14.48) | (13.54) | (13.69) | (13.53) | (13.67) | |
| Quarter Dummy - 1999q3 | -1.551 | -6.819 | -5.534 | -2.705 | -5.655 | -2.715 |
| (10.86) | (10.50) | (7.67) | (7.90) | (7.63) | (7.84) | |
| Quarter Dummy - 1999q4 | 19.086 | 13.390 | 14.027* | 16.431* | 14.109* | 16.573* |
| (11.60) | (11.23) | (8.39) | (8.52) | (8.35) | (8.47) | |
| Quarter Dummy - 2000q1 | 10.616 | 4.890 | 5.677 | 8.678 | 5.521 | 8.566 |
| (14.62) | (14.25) | (12.19) | (12.28) | (12.18) | (12.26) | |
| Quarter Dummy - 2000q2 | 13.856 | 8.882 | 3.833 | 6.861 | 3.505 | 6.482 |
| (12.74) | (12.39) | (8.89) | (9.11) | (8.89) | (9.11) | |
| Quarter Dummy - 2000q3 | 4.431 | 0.155 | -3.037 | 0.585 | -3.198 | 0.338 |
| (11.56) | (11.21) | (8.02) | (8.28) | (7.98) | (8.23) | |
| Quarter Dummy - 2000q4 | 26.848** | 22.243* | 21.613** | 25.170*** | 21.497** | 24.977*** |
| (11.91) | (11.58) | (9.13) | (9.37) | (9.10) | (9.32) | |
| Quarter Dummy - 2001q1 | 7.249 | 1.869 | 0.316 | 3.486 | 0.509 | 3.739 |
| (11.05) | (10.78) | (7.31) | (7.49) | (7.33) | (7.48) | |
| Quarter Dummy - 2001q2 | 27.105** | 22.776** | 21.844*** | 25.349*** | 21.762*** | 25.122*** |
| (11.54) | (11.25) | (8.41) | (8.59) | (8.40) | (8.56) | |
| Quarter Dummy - 2001q3 | 38.049** | 33.725** | 30.100** | 33.505** | 29.900** | 33.273** |
| (17.25) | (17.04) | (14.84) | (14.93) | (14.82) | (14.87) | |
| Quarter Dummy - 2001q4 | 25.577** | 21.346* | 19.988** | 23.202*** | 19.916** | 23.152*** |
| (11.68) | (11.41) | (8.48) | (8.58) | (8.44) | (8.51) | |
| Quarter Dummy - 2002q1 | -2.163 | -7.444 | -6.089 | -2.973 | -6.470 | -3.296 |
| (11.25) | (10.88) | (7.75) | (7.88) | (7.71) | (7.83) | |
| Quarter Dummy - 2002q2 | 16.215 | 11.587 | -16.839** | -13.546* | -16.903** | -13.697* |
| (30.63) | (30.65) | (6.97) | (7.11) | (6.90) | (7.02) | |
| Quarter Dummy - 2002q3 | -4.806 | -9.099 | -8.813 | -5.447 | -9.001 | -5.570 |
| (11.27) | (10.98) | (7.56) | (7.74) | (7.53) | (7.68) | |
| Quarter Dummy - 2002q4 | -15.006 | -19.809* | -17.800** | -14.723** | -18.010** | -14.919** |
| (11.24) | (10.91) | (7.20) | (7.33) | (7.18) | (7.30) | |
| Quarter Dummy - 2003q1 | 19.900 | 12.758 | -13.060 | -11.306 | -13.202 | -11.426 |
| (32.42) | (32.42) | (9.71) | (9.68) | (9.69) | (9.67) | |
| Quarter Dummy - 2003q2 | 8.112 | 0.811 | 3.412 | 4.307 | 3.283 | 4.167 |
| (14.46) | (14.09) | (11.22) | (11.24) | (11.20) | (11.23) | |
| Quarter Dummy - 2003q3 | 28.644 | 21.270 | 26.206 | 26.749 | 26.249 | 26.838 |
| (22.57) | (22.35) | (20.74) | (20.80) | (20.72) | (20.76) | |
| Quarter Dummy - 2003q4 | 6.330 | -1.677 | (dropped) | (dropped) | (dropped) | (dropped) |
| (11.43) | (11.04) | |||||
| Quarter Dummy - 2004q1 | 38.677 | 29.355 | 32.947 | 32.274 | 32.791 | 32.115 |
| (27.24) | (27.17) | (25.32) | (25.39) | (25.32) | (25.39) | |
| Quarter Dummy - 2004q2 | 20.677* | 11.786 | 18.266** | 18.175** | 18.337** | 18.191** |
| (12.24) | (11.98) | (7.24) | (7.47) | (7.19) | (7.43) | |
| Quarter Dummy - 2004q3 | 20.769* | 11.556 | 16.900** | 15.784* | 16.682** | 15.574* |
| (11.86) | (11.86) | (8.01) | (8.57) | (7.98) | (8.54) | |
| Quarter Dummy - 2004q4 | 59.296** | 52.007** | 56.325** | 56.904** | 55.578** | 55.994** |
| (23.64) | (23.61) | (22.15) | (22.23) | (22.16) | (22.25) | |
| Quarter Dummy - 2005q1 | 3.681 | -4.320 | 0.437 | 0.148 | 0.049 | -0.598 |
| (10.92) | (10.58) | (7.30) | (7.34) | (7.30) | (7.40) | |
| Quarter Dummy - 2005q2 | 30.406*** | 23.083** | 28.054*** | 28.060*** | 27.921*** | 27.573*** |
| (10.89) | (10.72) | (8.25) | (8.39) | (8.26) | (8.42) | |
| Quarter Dummy - 2005q3 | 40.040*** | 32.536*** | 38.230*** | 37.830*** | 37.470*** | 36.703*** |
| (11.80) | (11.53) | (8.72) | (8.90) | (8.69) | (8.87) | |
| Quarter Dummy - 2005q4 | 128.989** | 121.918** | 128.874** | 128.616** | 128.505** | 128.036** |
| (50.62) | (50.82) | (54.00) | (53.83) | (53.96) | (53.65) | |
| Quarter Dummy - 2006q1 | 64.630*** | 57.203*** | 50.870*** | 50.561*** | 50.520*** | 50.056*** |
| (21.18) | (21.13) | (17.18) | (17.29) | (17.14) | (17.26) | |
| Quarter Dummy - 2006q2 | 137.891*** | 130.803*** | 136.735*** | 136.721*** | 136.193*** | 135.855*** |
| (31.00) | (30.90) | (30.19) | (30.02) | (30.25) | (30.09) | |
| Quarter Dummy - 2006q3 | 93.895*** | 87.182*** | 92.858*** | 92.777*** | 92.429*** | 92.244*** |
| (22.07) | (21.83) | (21.51) | (21.54) | (21.51) | (21.56) | |
| Quarter Dummy - 2006q4 | 253.536*** | 246.280*** | 248.632*** | 248.196*** | 247.946*** | 247.244*** |
| (61.87) | (62.09) | (63.38) | (63.43) | (63.32) | (63.34) | |
| Quarter Dummy - 2007q1 | 130.805*** | 123.551*** | 130.875*** | 130.915*** | 129.895*** | 129.843*** |
| (33.66) | (34.07) | (34.15) | (34.29) | (34.08) | (34.23) | |
| Quarter Dummy - 2007q2 | 235.000*** | 228.081*** | 233.959*** | 233.710*** | 233.121*** | 232.790*** |
| (66.59) | (66.96) | (67.02) | (66.69) | (67.15) | (66.78) | |
| Quarter Dummy - 2007q3 | 67.148*** | 62.095*** | 67.681*** | 68.680*** | 67.297*** | 68.103*** |
| (13.34) | (13.20) | (13.07) | (13.27) | (12.99) | (13.21) | |
| Quarter Dummy - 2007q4 | 44.895*** | 42.107*** | 44.319*** | 47.506*** | 43.987*** | 46.344*** |
| (9.36) | (9.17) | (9.31) | (9.49) | (9.23) | (9.38) | |
| Quarter Dummy - 2008q1 | 21.783** | 21.170** | 23.003** | 28.130*** | 23.661*** | 27.249*** |
| (8.77) | (8.42) | (9.28) | (9.49) | (9.13) | (9.30) | |
| Quarter Dummy - 2008q2 | 18.477** | 20.136** | 17.895* | 24.707** | 18.639** | 23.384** |
| (8.61) | (8.20) | (9.39) | (9.65) | (9.26) | (9.37) | |
| Quarter Dummy - 2008q3 | 17.855** | 21.007*** | 19.720** | 27.135*** | 20.474** | 25.803*** |
| (7.88) | (7.47) | (9.86) | (10.13) | (9.67) | (9.73) | |
| Quarter Dummy - 2008q4 | 26.837** | 30.933*** | 31.194** | 39.306*** | 31.619** | 37.357*** |
| (11.69) | (11.35) | (13.96) | (14.23) | (13.75) | (13.87) | |
| Quarter Dummy - 2009q1 | 15.263** | 13.286* | 18.736* | 22.012** | 17.580* | 20.335* |
| (7.75) | (7.73) | (10.82) | (11.09) | (10.49) | (10.68) | |
| Quarter Dummy - 2009q2 | 8.133 | 7.204 | 10.541 | 14.034 | 8.979 | 11.908 |
| (6.84) | (6.79) | (10.78) | (11.01) | (10.42) | (10.59) | |
| Quarter Dummy - 2009q3 | 9.125 | 8.569 | 13.855 | 17.676* | 12.791 | 15.619 |
| (6.75) | (6.70) | (10.30) | (10.59) | (9.97) | (10.21) | |
| Quarter Dummy - 2009q4 | (dropped) | (dropped) | 4.020 | 8.409 | 3.443 | 6.845 |
| (10.79) | (11.05) | (10.52) | (10.65) | |||
| 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) | |
| 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.