| 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 | 24.089*** | 28.335*** | 19.284** | 22.794** | 18.346*** | 18.893** |
| (7.00) | (8.64) | (7.68) | (9.37) | (6.04) | (7.56) | |
| 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) | ||||
| 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 | 15.520 | 9.703 | 17.612 | 10.901 | 51.520*** | 52.347*** |
| (11.49) | (12.32) | (11.92) | (12.97) | (13.10) | (14.62) | |
| Other Mining Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Strip/Quarry/Pit Subunit Dummy | -2.122 | (dropped) | 0.245 | -3.919 | -17.622 | -30.635*** |
| (16.57) | (17.67) | (10.41) | (25.20) | (10.48) | ||
| Surface at Underground Subunit | -3.410 | -7.152* | -3.276 | -7.047** | -1.968 | -4.843 |
| Dummy | (2.94) | (3.88) | (2.79) | (3.59) | (3.08) | (3.93) |
| Underground Subunit Dummy | (dropped) | 10.538 | (dropped) | (dropped) | (dropped) | (dropped) |
| (9.03) | ||||||
| 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) | ||||
| MSHA Coal District 1 Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| MSHA Coal District 2 Dummy | 88.957*** | 70.308*** | 97.928*** | 77.206*** | 20.244 | 13.755 |
| (17.83) | (19.94) | (19.14) | (21.28) | (17.78) | (20.80) | |
| MSHA Coal District 3 Dummy | 48.576*** | 31.220* | 54.573*** | 34.097* | -14.723 | -24.900 |
| (15.61) | (18.37) | (16.90) | (20.16) | (15.48) | (18.77) | |
| MSHA Coal District 4 Dummy | 28.538* | 1.640 | 35.363** | 7.561 | -42.332*** | -60.794*** |
| (15.54) | (18.33) | (16.61) | (19.67) | (15.45) | (18.66) | |
| MSHA Coal District 5 Dummy | 40.683** | 21.060 | 47.005*** | 24.344 | -29.541* | -40.983** |
| (16.43) | (18.98) | (17.39) | (20.29) | (17.03) | (20.52) | |
| MSHA Coal District 6 Dummy | 34.405** | 17.488 | 41.897** | 22.961 | -36.461** | -44.659** |
| (15.74) | (17.98) | (16.81) | (19.33) | (15.74) | (18.89) | |
| MSHA Coal District 7 Dummy | 41.080*** | 19.576 | 49.914*** | 27.131 | -29.349* | -41.526** |
| (15.64) | (18.23) | (16.72) | (19.59) | (15.69) | (18.93) | |
| MSHA Coal District 8 Dummy | 24.843 | 12.745 | 30.264 | 16.374 | -14.354 | -28.529 |
| (25.15) | (23.63) | (25.05) | (23.77) | (20.04) | (22.27) | |
| MSHA Coal District 9 Dummy | 18.556 | -17.519 | 14.883 | -18.598 | -69.070*** | -106.347*** |
| (17.09) | (21.73) | (18.26) | (23.56) | (17.03) | (22.80) | |
| MSHA Coal District 10 Dummy | 99.950*** | 82.673*** | 119.061*** | 100.109*** | 69.356*** | 65.322*** |
| (18.67) | (22.36) | (19.83) | (24.10) | (19.48) | (24.21) | |
| MSHA Coal District 11 Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| MSHA Coal District 12 Dummy | 35.701** | 13.479 | 44.192*** | 19.023 | -32.057** | -48.022** |
| (15.56) | (17.90) | (16.57) | (19.27) | (15.62) | (18.70) | |
| 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 | -35.654*** | (dropped) | -17.995** | (dropped) | -8.688 | (dropped) |
| (9.04) | (8.86) | (9.17) | ||||
| Quarter Dummy - 1995q2 | -33.790*** | (dropped) | -18.669** | (dropped) | -10.222 | (dropped) |
| (9.05) | (9.02) | (9.55) | ||||
| Quarter Dummy - 1995q3 | -41.633*** | (dropped) | -27.994*** | (dropped) | -18.637** | (dropped) |
| (9.00) | (8.84) | (9.12) | ||||
| Quarter Dummy - 1995q4 | -95.319*** | (dropped) | -81.278*** | (dropped) | -71.933*** | (dropped) |
| (9.07) | (9.06) | (9.54) | ||||
| Quarter Dummy - 1996q1 | -83.625*** | (dropped) | -66.975*** | (dropped) | -57.940*** | (dropped) |
| (9.72) | (9.10) | (9.72) | ||||
| Quarter Dummy - 1996q2 | -45.603*** | (dropped) | -29.581*** | (dropped) | -19.275* | (dropped) |
| (9.63) | (9.47) | (10.08) | ||||
| Quarter Dummy - 1996q3 | -29.331*** | (dropped) | -14.246 | (dropped) | -3.163 | (dropped) |
| (9.37) | (9.16) | (9.33) | ||||
| Quarter Dummy - 1996q4 | -91.783*** | (dropped) | -76.751*** | (dropped) | -66.993*** | (dropped) |
| (9.82) | (9.51) | (9.92) | ||||
| Quarter Dummy - 1997q1 | -82.529*** | (dropped) | -64.245*** | (dropped) | -53.492*** | (dropped) |
| (9.48) | (9.19) | (9.67) | ||||
| Quarter Dummy - 1997q2 | -42.864*** | (dropped) | -25.674*** | (dropped) | -15.127 | (dropped) |
| (9.27) | (9.12) | (9.36) | ||||
| Quarter Dummy - 1997q3 | -47.144*** | (dropped) | -32.170*** | (dropped) | -20.575** | (dropped) |
| (9.28) | (9.38) | (9.72) | ||||
| Quarter Dummy - 1997q4 | -88.510*** | (dropped) | -73.946*** | (dropped) | -62.755*** | (dropped) |
| (9.30) | (8.86) | (9.19) | ||||
| Quarter Dummy - 1998q1 | -85.205*** | -81.111*** | -66.677*** | -67.398*** | -57.377*** | -56.481*** |
| (9.15) | (10.03) | (8.92) | (9.62) | (9.55) | (9.70) | |
| Quarter Dummy - 1998q2 | -41.813*** | -38.019*** | -23.638** | -24.688** | -13.405 | -13.074 |
| (9.70) | (10.46) | (9.30) | (9.82) | (9.91) | (9.91) | |
| Quarter Dummy - 1998q3 | -28.278*** | -24.289** | -13.398 | -14.346 | -2.175 | -1.659 |
| (9.13) | (9.97) | (9.28) | (8.90) | (9.54) | (8.97) | |
| Quarter Dummy - 1998q4 | -99.536*** | -95.676*** | -83.899*** | -84.920*** | -76.536*** | -76.506*** |
| (9.82) | (10.45) | (9.41) | (10.13) | (10.18) | (10.16) | |
| Quarter Dummy - 1999q1 | -82.441*** | -85.002*** | -64.991*** | -69.015*** | -58.448*** | -67.324*** |
| (9.91) | (9.24) | (9.65) | (8.56) | (10.54) | (8.84) | |
| Quarter Dummy - 1999q2 | -30.266*** | -33.031*** | -11.642 | -16.134** | -5.391 | -15.246** |
| (9.26) | (8.44) | (9.37) | (7.33) | (9.71) | (7.50) | |
| Quarter Dummy - 1999q3 | -27.857*** | -30.762*** | -12.622 | -17.047** | -5.361 | -15.291** |
| (9.62) | (8.87) | (9.38) | (7.30) | (9.73) | (7.53) | |
| Quarter Dummy - 1999q4 | -84.527*** | -87.459*** | -69.035*** | -73.565*** | -62.804*** | -72.690*** |
| (9.18) | (8.56) | (9.19) | (7.51) | (9.64) | (7.58) | |
| Quarter Dummy - 2000q1 | -80.689*** | -83.145*** | -61.939*** | -65.966*** | -57.888*** | -66.437*** |
| (10.20) | (9.69) | (9.47) | (9.07) | (10.13) | (9.28) | |
| Quarter Dummy - 2000q2 | -33.347*** | -35.997*** | -16.315* | -20.531*** | -10.307 | -19.296*** |
| (10.00) | (9.28) | (9.36) | (7.03) | (9.58) | (7.39) | |
| Quarter Dummy - 2000q3 | -16.442 | -19.257** | 0.869 | -3.757 | 7.176 | -2.565 |
| (10.41) | (9.58) | (10.24) | (6.41) | (10.24) | (6.63) | |
| Quarter Dummy - 2000q4 | -69.232*** | -71.574*** | -52.875*** | -56.919*** | -47.021*** | -55.953*** |
| (9.19) | (8.61) | (8.88) | (7.30) | (9.41) | (7.40) | |
| Quarter Dummy - 2001q1 | -62.061*** | -64.478*** | -41.473*** | -44.921*** | -36.876*** | -45.161*** |
| (9.56) | (9.07) | (9.35) | (7.68) | (9.71) | (7.80) | |
| Quarter Dummy - 2001q2 | -35.360*** | -38.304*** | -18.345* | -23.085*** | -12.714 | -22.549*** |
| (9.36) | (8.62) | (9.47) | (7.12) | (9.94) | (7.34) | |
| Quarter Dummy - 2001q3 | -26.189** | -28.780*** | -11.843 | -16.230** | -4.446 | -14.220* |
| (10.20) | (9.43) | (9.99) | (7.67) | (10.26) | (7.83) | |
| Quarter Dummy - 2001q4 | -51.737*** | -53.989*** | -36.779*** | -40.658*** | -30.100*** | -39.340*** |
| (9.24) | (8.60) | (9.53) | (7.26) | (9.93) | (7.26) | |
| Quarter Dummy - 2002q1 | -32.079*** | -34.808*** | -14.337 | -18.500** | -8.793 | -18.157** |
| (10.08) | (9.44) | (9.69) | (7.41) | (10.05) | (7.64) | |
| Quarter Dummy - 2002q2 | -27.465*** | -30.970*** | -11.759 | -16.863** | -6.309 | -17.178** |
| (9.77) | (9.21) | (9.53) | (7.09) | (10.20) | (7.28) | |
| Quarter Dummy - 2002q3 | -31.514*** | -34.852*** | -17.950** | -23.059*** | -10.343 | -21.136*** |
| (9.29) | (8.74) | (8.83) | (7.15) | (9.50) | (7.24) | |
| Quarter Dummy - 2002q4 | -28.625*** | -32.223*** | -13.233 | -18.734** | -7.737 | -18.550** |
| (10.13) | (9.49) | (10.28) | (8.31) | (10.56) | (8.53) | |
| Quarter Dummy - 2003q1 | -21.491** | -26.190*** | 0.029 | -5.906 | 3.395 | -7.959 |
| (10.10) | (9.68) | (9.75) | (7.36) | (9.73) | (7.51) | |
| Quarter Dummy - 2003q2 | -30.809*** | -35.806*** | -12.265 | -18.730** | -7.528 | -19.336** |
| (10.66) | (10.12) | (9.94) | (8.93) | (10.31) | (9.15) | |
| Quarter Dummy - 2003q3 | -26.571*** | -31.758*** | -8.854 | -15.741*** | -3.147 | -15.999*** |
| (10.12) | (9.50) | (10.10) | (5.67) | (10.30) | (5.85) | |
| Quarter Dummy - 2003q4 | -40.939*** | -45.458*** | -22.459** | -28.648*** | -17.723* | -29.628*** |
| (10.03) | (9.30) | (9.54) | (8.81) | (9.87) | (9.05) | |
| Quarter Dummy - 2004q1 | -14.176 | -18.219* | 5.719 | (dropped) | 10.463 | (dropped) |
| (10.64) | (10.07) | (11.06) | (11.35) | |||
| Quarter Dummy - 2004q2 | -9.296 | -13.589 | 10.105 | 3.998 | 16.366 | 5.119 |
| (10.39) | (9.87) | (9.93) | (6.92) | (10.35) | (7.00) | |
| Quarter Dummy - 2004q3 | -6.959 | -11.162 | 10.733 | 5.133 | 17.759 | 6.504 |
| (11.29) | (10.81) | (10.61) | (9.50) | (10.96) | (9.54) | |
| Quarter Dummy - 2004q4 | -28.169*** | -32.291*** | -9.733 | -15.468* | -4.740 | -15.727* |
| (10.79) | (10.42) | (10.90) | (8.70) | (11.24) | (9.08) | |
| Quarter Dummy - 2005q1 | 4.445 | -0.042 | 25.540** | 19.519** | 30.018*** | 18.964** |
| (10.68) | (10.16) | (10.66) | (8.09) | (10.65) | (8.21) | |
| Quarter Dummy - 2005q2 | 13.741 | 9.051 | 33.495*** | 27.194*** | 39.993*** | 28.631*** |
| (9.09) | (9.10) | (9.45) | (8.32) | (9.46) | (8.63) | |
| Quarter Dummy - 2005q3 | 1.701 | -3.114 | 20.295** | 13.781* | 28.533*** | 16.867* |
| (8.47) | (8.45) | (8.81) | (8.27) | (9.35) | (8.80) | |
| Quarter Dummy - 2005q4 | -22.591** | -27.691*** | -5.656 | -12.802 | 4.993 | -7.185 |
| (10.48) | (10.40) | (10.40) | (10.51) | (10.76) | (10.61) | |
| Quarter Dummy - 2006q1 | 11.525 | 6.613 | 34.193*** | 27.405** | 44.141*** | 32.000*** |
| (12.41) | (11.91) | (12.16) | (11.27) | (12.75) | (10.88) | |
| Quarter Dummy - 2006q2 | -14.542 | -20.107* | 6.267 | -1.076 | 14.265 | 1.644 |
| (13.12) | (12.06) | (14.02) | (9.78) | (14.28) | (10.23) | |
| Quarter Dummy - 2006q3 | 38.561*** | 33.553** | 58.506*** | 51.375*** | 70.638*** | 58.266*** |
| (14.72) | (14.49) | (15.90) | (14.55) | (16.67) | (14.99) | |
| Quarter Dummy - 2006q4 | -45.823*** | -50.720*** | -28.612** | -35.683** | -16.407 | -27.898** |
| (14.02) | (13.87) | (13.33) | (14.00) | (13.28) | (13.69) | |
| Quarter Dummy - 2007q1 | -13.312 | -17.593 | 10.146 | 4.208 | 20.209 | 10.074 |
| (13.02) | (12.22) | (13.27) | (10.54) | (13.52) | (10.96) | |
| Quarter Dummy - 2007q2 | -4.350 | -9.746 | 15.865 | 8.454 | 30.597** | 18.797 |
| (11.21) | (11.47) | (12.23) | (11.31) | (12.85) | (12.17) | |
| Quarter Dummy - 2007q3 | 14.429 | 10.519 | 30.057** | 24.170* | 43.590*** | 32.831** |
| (10.79) | (11.30) | (11.70) | (13.26) | (12.35) | (13.79) | |
| Quarter Dummy - 2007q4 | 27.294*** | 24.237** | 41.299*** | 36.782*** | 46.499*** | 37.168*** |
| (9.74) | (9.86) | (9.24) | (9.86) | (9.86) | (10.83) | |
| Quarter Dummy - 2008q1 | 24.213*** | 21.453** | 44.888*** | 41.207*** | 43.683*** | 35.885*** |
| (9.16) | (9.10) | (9.55) | (9.75) | (10.03) | (9.51) | |
| Quarter Dummy - 2008q2 | 16.771* | 14.905* | 36.475*** | 33.800*** | 30.170*** | 23.521** |
| (8.66) | (8.59) | (8.25) | (9.63) | (8.63) | (9.85) | |
| Quarter Dummy - 2008q3 | 10.109 | 8.820 | 21.795** | 19.016* | 18.509** | 12.516 |
| (9.35) | (9.26) | (8.51) | (9.87) | (9.27) | (10.22) | |
| Quarter Dummy - 2008q4 | -14.161 | -15.066* | -0.114 | -2.102 | -5.965 | -11.191 |
| (9.14) | (9.01) | (8.48) | (10.46) | (9.22) | (11.16) | |
| Quarter Dummy - 2009q1 | -15.946* | -16.502** | -3.103 | -4.678 | 0.553 | -7.961 |
| (8.25) | (8.16) | (8.35) | (9.69) | (9.05) | (10.64) | |
| Quarter Dummy - 2009q2 | -8.643 | -8.838 | 2.547 | 1.161 | 5.878 | -3.377 |
| (9.00) | (8.92) | (7.53) | (10.56) | (7.99) | (11.20) | |
| Quarter Dummy - 2009q3 | -7.735 | -8.094 | (dropped) | -1.683 | (dropped) | -9.262 |
| (7.51) | (7.48) | (10.40) | (11.18) | |||
| Quarter Dummy - 2009q4 | (dropped) | (dropped) | 7.367 | 6.836 | 5.127 | -3.409 |
| (7.78) | (11.01) | (8.39) | (11.74) | |||
| 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) | |
| 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 |
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.