| 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 | 1.310 | 1.996 | 0.805 | 1.400 | -0.373 | -0.663 |
| (1.50) | (2.08) | (1.57) | (2.18) | (1.45) | (1.91) | |
| Union X Mine Size | -1.094 | -1.638 | -1.366 | -2.066 | 3.120 | 3.655 |
| (1.35) | (1.65) | (1.55) | (1.92) | (5.57) | (6.40) | |
| Mine Size | 8.261*** | 9.664*** | 9.597*** | 11.303*** | 11.029*** | 12.190*** |
| (1.20) | (1.46) | (1.34) | (1.80) | (2.90) | (3.25) | |
| Log of Controller Size | 0.497*** | 0.670** | 0.572** | 0.771** | 0.882*** | 0.978*** |
| (0.19) | (0.29) | (0.23) | (0.36) | (0.19) | (0.29) | |
| Lost-Day Injuries in Prev. Year | 0.632*** | 0.594*** | 0.645*** | 0.611*** | 1.035*** | 1.025*** |
| (0.23) | (0.22) | (0.22) | (0.22) | (0.23) | (0.21) | |
| Penalty Pts. in Prev. Year | 2.455*** | 2.236*** | 2.473*** | 2.253*** | 2.744*** | 2.501*** |
| (0.12) | (0.14) | (0.13) | (0.15) | (0.10) | (0.14) | |
| Mine Age | 0.248*** | 0.295*** | 0.260*** | 0.309*** | 0.284*** | 0.315*** |
| (0.08) | (0.09) | (0.08) | (0.09) | (0.07) | (0.08) | |
| Productivity | -0.291*** | -0.267*** | -0.296*** | -0.284*** | -0.553*** | -0.619*** |
| (0.06) | (0.09) | (0.06) | (0.09) | (0.07) | (0.09) | |
| NIOSH Longwall Dummy | 4.290 | 3.724 | 9.025*** | |||
| (3.65) | (3.80) | (3.50) | ||||
| Number of Coal Beds | 2.017 | 2.091 | 4.137 | |||
| (3.32) | (3.33) | (3.25) | ||||
| Avg. Coal Bed Thickness (yds.) | 0.783 | 0.568 | 1.205 | |||
| (1.40) | (1.45) | (1.45) | ||||
| Subsidiary Indicator | -0.640 | -0.508 | 0.362 | |||
| (1.06) | (1.16) | (1.12) | ||||
| Pct. Captive Production | -1.768* | -2.004* | -1.809* | |||
| (1.02) | (1.08) | (1.03) | ||||
| 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 | 0.106 | 0.672 | 0.248 | 0.952 | 4.006 | 5.183* |
| (2.77) | (3.20) | (2.79) | (3.26) | (2.50) | (3.00) | |
| Other Mining Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Strip/Quarry/Pit Subunit Dummy | -4.075*** | (dropped) | -3.710*** | (dropped) | -4.288*** | (dropped) |
| (1.11) | (1.16) | (1.08) | ||||
| Surface at Underground Subunit | -1.504** | -1.340 | -1.419** | -1.296 | -1.141* | -0.962 |
| Dummy | (0.67) | (0.85) | (0.68) | (0.87) | (0.68) | (0.86) |
| Underground Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Pct. Continuous Mining Method | 0.021* | 0.032*** | 0.039*** | |||
| (0.01) | (0.01) | (0.01) | ||||
| Pct. Conventional Mining Method | 0.027** | 0.035*** | 0.043*** | |||
| (0.01) | (0.01) | (0.01) | ||||
| Pct. Longwall Mining Method | 0.005 | 0.009 | 0.083 | |||
| (0.06) | (0.06) | (0.06) | ||||
| Pct. Shortwall Mining Method | 0.545 | 0.533 | 0.598 | |||
| (0.41) | (0.40) | (0.43) | ||||
| MSHA Coal District 1 Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| MSHA Coal District 2 Dummy | -15.980*** | -18.100*** | -16.549*** | -17.403*** | -19.922*** | -20.852*** |
| (3.70) | (6.75) | (3.46) | (4.87) | (3.42) | (4.75) | |
| MSHA Coal District 3 Dummy | -5.382 | -5.709 | -6.286 | -5.550 | -9.492** | -9.430* |
| (4.09) | (6.78) | (3.98) | (5.56) | (3.77) | (5.22) | |
| MSHA Coal District 4 Dummy | -11.063*** | -11.904* | -11.879*** | -11.522** | -15.313*** | -15.277*** |
| (3.29) | (6.62) | (3.11) | (4.57) | (3.14) | (4.49) | |
| MSHA Coal District 5 Dummy | -11.162*** | -10.760 | -12.110*** | -10.636** | -15.569*** | -14.440*** |
| (3.33) | (6.57) | (3.15) | (4.67) | (3.12) | (4.55) | |
| MSHA Coal District 6 Dummy | -8.123** | -8.998 | -8.942*** | -8.698* | -12.649*** | -12.819*** |
| (3.39) | (6.46) | (3.20) | (4.70) | (3.17) | (4.56) | |
| MSHA Coal District 7 Dummy | -5.739* | -6.813 | -6.557** | -6.398 | -10.345*** | -10.578** |
| (3.44) | (6.54) | (3.26) | (4.75) | (3.22) | (4.58) | |
| MSHA Coal District 8 Dummy | -3.533 | -6.048 | -4.582 | -5.920 | -4.418 | -7.220 |
| (5.74) | (7.71) | (5.72) | (6.78) | (5.59) | (6.62) | |
| MSHA Coal District 9 Dummy | -7.076 | -10.405 | -8.996** | -11.065* | -12.764*** | -16.915*** |
| (4.33) | (6.54) | (4.23) | (5.70) | (4.12) | (5.45) | |
| MSHA Coal District 10 Dummy | (dropped) | -1.243 | (dropped) | (dropped) | (dropped) | (dropped) |
| (7.63) | ||||||
| MSHA Coal District 11 Dummy | 3.027 | (dropped) | 1.321 | -0.340 | 4.752 | 2.533 |
| (6.36) | (6.44) | (7.61) | (6.34) | (7.35) | ||
| MSHA Coal District 12 Dummy | -11.300*** | -12.911** | -12.051*** | -12.536*** | -15.418*** | -16.466*** |
| (3.35) | (6.53) | (3.18) | (4.66) | (3.13) | (4.52) | |
| 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 | 12.129*** | (dropped) | 0.082 | (dropped) | 0.536 | (dropped) |
| (2.38) | (1.32) | (1.33) | ||||
| Quarter Dummy - 1995q2 | 12.460*** | (dropped) | 0.254 | (dropped) | 0.637 | (dropped) |
| (2.36) | (1.37) | (1.39) | ||||
| Quarter Dummy - 1995q3 | 10.497*** | (dropped) | -1.848 | (dropped) | -1.343 | (dropped) |
| (2.31) | (1.39) | (1.40) | ||||
| Quarter Dummy - 1995q4 | 10.638*** | (dropped) | -1.562 | (dropped) | -1.098 | (dropped) |
| (2.30) | (1.27) | (1.30) | ||||
| Quarter Dummy - 1996q1 | 9.927*** | (dropped) | -2.316* | (dropped) | -1.839 | (dropped) |
| (2.33) | (1.32) | (1.33) | ||||
| Quarter Dummy - 1996q2 | 10.716*** | (dropped) | -1.608 | (dropped) | -1.004 | (dropped) |
| (2.29) | (1.29) | (1.31) | ||||
| Quarter Dummy - 1996q3 | 11.851*** | (dropped) | -0.431 | (dropped) | 0.279 | (dropped) |
| (2.34) | (1.31) | (1.34) | ||||
| Quarter Dummy - 1996q4 | 10.093*** | (dropped) | -2.065 | (dropped) | -1.507 | (dropped) |
| (2.43) | (1.35) | (1.39) | ||||
| Quarter Dummy - 1997q1 | 10.902*** | (dropped) | -1.434 | (dropped) | -0.734 | (dropped) |
| (2.34) | (1.32) | (1.36) | ||||
| Quarter Dummy - 1997q2 | 11.097*** | (dropped) | -1.088 | (dropped) | -0.459 | (dropped) |
| (2.32) | (1.38) | (1.40) | ||||
| Quarter Dummy - 1997q3 | 10.838*** | (dropped) | -1.344 | (dropped) | -0.604 | (dropped) |
| (2.31) | (1.37) | (1.39) | ||||
| Quarter Dummy - 1997q4 | 9.851*** | (dropped) | -2.404* | (dropped) | -1.757 | (dropped) |
| (2.32) | (1.38) | (1.40) | ||||
| Quarter Dummy - 1998q1 | 10.230*** | 9.202*** | -1.489 | 5.627* | -0.987 | 7.340** |
| (2.34) | (3.00) | (1.49) | (2.97) | (1.50) | (2.89) | |
| Quarter Dummy - 1998q2 | 9.135*** | 8.123*** | -2.616* | 4.544 | -1.995 | 6.370** |
| (2.24) | (2.89) | (1.34) | (2.85) | (1.35) | (2.78) | |
| Quarter Dummy - 1998q3 | 11.935*** | 10.882*** | -0.516 | 6.528** | 0.192 | 8.483*** |
| (2.34) | (2.92) | (1.36) | (2.92) | (1.35) | (2.84) | |
| Quarter Dummy - 1998q4 | 9.616*** | 8.567*** | -2.664** | 4.398 | -2.334* | 5.914** |
| (2.28) | (2.86) | (1.31) | (2.84) | (1.34) | (2.81) | |
| Quarter Dummy - 1999q1 | 10.127*** | 8.576*** | -1.768 | 5.031** | -1.599 | 5.612** |
| (2.31) | (2.51) | (1.30) | (2.37) | (1.34) | (2.36) | |
| Quarter Dummy - 1999q2 | 9.124*** | 7.557*** | -2.917** | 3.893 | -2.738** | 4.464* |
| (2.28) | (2.49) | (1.38) | (2.37) | (1.39) | (2.35) | |
| Quarter Dummy - 1999q3 | 9.680*** | 8.158*** | -2.583* | 4.222* | -2.313* | 4.890** |
| (2.36) | (2.58) | (1.39) | (2.44) | (1.39) | (2.40) | |
| Quarter Dummy - 1999q4 | 10.356*** | 8.849*** | -1.963 | 4.841* | -1.833 | 5.366** |
| (2.49) | (2.70) | (1.41) | (2.58) | (1.44) | (2.54) | |
| Quarter Dummy - 2000q1 | 10.831*** | 9.274*** | -0.924 | 5.891** | -1.021 | 6.222** |
| (2.50) | (2.72) | (1.45) | (2.56) | (1.50) | (2.55) | |
| Quarter Dummy - 2000q2 | 11.048*** | 9.430*** | -0.989 | 5.721** | -0.892 | 6.233** |
| (2.46) | (2.64) | (1.30) | (2.46) | (1.34) | (2.45) | |
| Quarter Dummy - 2000q3 | 12.462*** | 10.849*** | 0.163 | 6.849*** | 0.333 | 7.424*** |
| (2.41) | (2.57) | (1.35) | (2.41) | (1.37) | (2.40) | |
| Quarter Dummy - 2000q4 | 13.236*** | 11.620*** | 0.603 | 7.315*** | 0.697 | 7.837*** |
| (2.32) | (2.50) | (1.35) | (2.34) | (1.37) | (2.33) | |
| Quarter Dummy - 2001q1 | 14.054*** | 12.479*** | 2.375* | 9.221*** | 2.391* | 9.649*** |
| (2.45) | (2.65) | (1.39) | (2.52) | (1.41) | (2.49) | |
| Quarter Dummy - 2001q2 | 14.242*** | 12.615*** | 2.307* | 9.022*** | 2.415* | 9.551*** |
| (2.45) | (2.63) | (1.33) | (2.52) | (1.36) | (2.52) | |
| Quarter Dummy - 2001q3 | 14.987*** | 13.427*** | 2.460* | 9.193*** | 2.750* | 9.917*** |
| (2.51) | (2.69) | (1.47) | (2.61) | (1.52) | (2.60) | |
| Quarter Dummy - 2001q4 | 13.827*** | 12.261*** | 1.575 | 8.326*** | 1.823 | 8.997*** |
| (2.56) | (2.75) | (1.48) | (2.68) | (1.51) | (2.64) | |
| Quarter Dummy - 2002q1 | 11.880*** | 10.234*** | -0.147 | 6.549** | -0.029 | 7.073*** |
| (2.57) | (2.78) | (1.41) | (2.65) | (1.43) | (2.63) | |
| Quarter Dummy - 2002q2 | 9.004*** | 7.317*** | -3.207*** | 3.388 | -3.090** | 3.881 |
| (2.42) | (2.61) | (1.19) | (2.44) | (1.23) | (2.45) | |
| Quarter Dummy - 2002q3 | 10.374*** | 8.698*** | -2.127 | 4.476* | -1.881 | 5.126** |
| (2.54) | (2.73) | (1.35) | (2.58) | (1.39) | (2.58) | |
| Quarter Dummy - 2002q4 | 8.932*** | 7.172*** | -3.170** | 3.379 | -3.083** | 3.858 |
| (2.47) | (2.66) | (1.30) | (2.55) | (1.34) | (2.56) | |
| Quarter Dummy - 2003q1 | 11.416*** | 9.786*** | -0.332 | 6.411** | -0.361 | 6.725*** |
| (2.47) | (2.64) | (1.30) | (2.58) | (1.34) | (2.52) | |
| Quarter Dummy - 2003q2 | 12.117*** | 10.394*** | 0.171 | 6.797*** | 0.256 | 7.247*** |
| (2.49) | (2.63) | (1.31) | (2.51) | (1.35) | (2.49) | |
| Quarter Dummy - 2003q3 | 13.462*** | 11.799*** | 1.513 | 8.181*** | 1.647 | 8.638*** |
| (2.47) | (2.66) | (1.20) | (2.48) | (1.21) | (2.45) | |
| Quarter Dummy - 2003q4 | 11.921*** | 10.287*** | (dropped) | 6.659*** | (dropped) | 7.000*** |
| (2.49) | (2.66) | (2.58) | (2.56) | |||
| Quarter Dummy - 2004q1 | 12.961*** | 11.350*** | 1.023 | 7.783*** | 1.041 | 8.231*** |
| (2.63) | (2.84) | (1.25) | (2.77) | (1.23) | (2.75) | |
| Quarter Dummy - 2004q2 | 14.684*** | 13.066*** | 3.031*** | 9.732*** | 3.129*** | 10.260*** |
| (2.67) | (2.86) | (1.14) | (2.76) | (1.17) | (2.76) | |
| Quarter Dummy - 2004q3 | 14.782*** | 13.273*** | 3.227** | 10.104*** | 3.505*** | 10.788*** |
| (2.62) | (2.76) | (1.29) | (2.75) | (1.33) | (2.73) | |
| Quarter Dummy - 2004q4 | 14.258*** | 12.727*** | 2.373* | 9.177*** | 2.421** | 9.603*** |
| (2.51) | (2.64) | (1.22) | (2.54) | (1.23) | (2.52) | |
| Quarter Dummy - 2005q1 | 14.432*** | 12.840*** | 2.866* | 9.616*** | 2.896* | 10.053*** |
| (2.52) | (2.66) | (1.50) | (2.61) | (1.55) | (2.61) | |
| Quarter Dummy - 2005q2 | 15.061*** | 13.454*** | 3.285* | 10.001*** | 3.509** | 10.630*** |
| (2.49) | (2.58) | (1.74) | (2.47) | (1.78) | (2.41) | |
| Quarter Dummy - 2005q3 | 14.014*** | 12.355*** | 2.216 | 8.867*** | 2.665 | 9.728*** |
| (2.40) | (2.52) | (1.59) | (2.33) | (1.64) | (2.28) | |
| Quarter Dummy - 2005q4 | 14.799*** | 13.148*** | 2.792* | 9.410*** | 3.426** | 10.495*** |
| (2.36) | (2.49) | (1.45) | (2.42) | (1.51) | (2.37) | |
| Quarter Dummy - 2006q1 | 17.029*** | 15.365*** | 5.219*** | 11.866*** | 5.800*** | 12.839*** |
| (2.85) | (3.01) | (1.82) | (2.87) | (1.86) | (2.89) | |
| Quarter Dummy - 2006q2 | 16.630*** | 14.931*** | 4.802*** | 11.408*** | 5.250*** | 12.226*** |
| (2.80) | (2.96) | (1.61) | (2.81) | (1.67) | (2.86) | |
| Quarter Dummy - 2006q3 | 18.589*** | 16.908*** | 6.576*** | 13.129*** | 7.405*** | 14.374*** |
| (2.71) | (2.74) | (1.86) | (2.56) | (1.91) | (2.58) | |
| Quarter Dummy - 2006q4 | 14.930*** | 13.186*** | 3.019** | 9.512*** | 3.933** | 10.915*** |
| (2.52) | (2.67) | (1.51) | (2.59) | (1.57) | (2.59) | |
| Quarter Dummy - 2007q1 | 15.559*** | 13.928*** | 4.035** | 10.764*** | 4.792*** | 11.986*** |
| (2.43) | (2.55) | (1.70) | (2.43) | (1.81) | (2.42) | |
| Quarter Dummy - 2007q2 | 19.350*** | 17.513*** | 7.449*** | 13.916*** | 8.583*** | 15.508*** |
| (2.52) | (2.56) | (2.04) | (2.39) | (2.17) | (2.43) | |
| Quarter Dummy - 2007q3 | 14.938*** | 13.550*** | 2.776 | 9.603*** | 3.759* | 11.101*** |
| (2.41) | (2.47) | (1.87) | (2.36) | (1.94) | (2.37) | |
| Quarter Dummy - 2007q4 | 17.054*** | 16.090*** | 4.624** | 11.928*** | 4.794** | 12.601*** |
| (2.47) | (2.47) | (2.23) | (2.42) | (2.27) | (2.45) | |
| Quarter Dummy - 2008q1 | 10.521*** | 10.039*** | -1.189 | 6.667*** | -1.681 | 6.815*** |
| (2.29) | (2.25) | (2.10) | (2.21) | (2.05) | (2.28) | |
| Quarter Dummy - 2008q2 | 8.384*** | 8.318*** | -3.412 | 4.863** | -4.427** | 4.493* |
| (2.33) | (2.30) | (2.34) | (2.28) | (2.25) | (2.33) | |
| Quarter Dummy - 2008q3 | 8.376*** | 8.512*** | -4.519** | 3.867* | -5.215** | 3.959* |
| (2.34) | (2.29) | (2.24) | (2.27) | (2.15) | (2.34) | |
| Quarter Dummy - 2008q4 | 3.872 | 4.191 | -8.398*** | 0.177 | -9.394*** | -0.025 |
| (2.67) | (2.61) | (2.43) | (2.45) | (2.39) | (2.52) | |
| Quarter Dummy - 2009q1 | 2.155 | 1.979 | -10.170*** | -2.000 | -10.006*** | -1.580 |
| (2.35) | (2.30) | (2.13) | (2.12) | (2.14) | (2.17) | |
| Quarter Dummy - 2009q2 | 1.969 | 1.885 | -10.564*** | -2.363 | -10.450*** | -2.095 |
| (2.20) | (2.16) | (2.47) | (1.74) | (2.45) | (1.77) | |
| Quarter Dummy - 2009q3 | 4.084** | 4.074** | -8.257*** | (dropped) | -8.474*** | (dropped) |
| (2.05) | (2.02) | (2.45) | (2.41) | |||
| Quarter Dummy - 2009q4 | (dropped) | (dropped) | -12.280*** | -3.946* | -12.800*** | -4.303** |
| (2.62) | (2.08) | (2.54) | (2.13) | |||
| Constant | 8.419** | 4.875 | 21.087*** | 7.248 | 29.067*** | 12.695** |
| (3.94) | (7.38) | (3.59) | (6.44) | (3.52) | (6.29) | |
| Observations | 23,380 | 16,790 | 22,704 | 16,324 | 22,704 | 16,324 |
| # 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 | 0.62 | 0.64 | 0.62 | 0.64 | 0.61 | 0.63 |
| Regression Date/Time | 12/2/11 16:46 | 12/2/11 16:46 | 12/2/11 16:46 | 12/2/11 16:46 | 12/2/11 16:47 | 12/2/11 16:47 |
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 number of violations per mine-quarter.