| 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) | ||||
| 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 | -0.021** | -0.019** | -0.020** | -0.019** | -0.016* | -0.014* |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Other Mining Subunit Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| Strip/Quarry/Pit Subunit Dummy | (dropped) | -0.416*** | -0.228 | (dropped) | -0.231 | -0.430*** |
| (0.01) | (0.16) | (0.17) | (0.01) | |||
| Surface at Underground Subunit | -0.002 | 0.000 | -0.002 | 0.000 | -0.002 | 0.000 |
| Dummy | (0.00) | (0.00) | (0.00) | (0.00) | (0.00) | (0.00) |
| Underground Subunit Dummy | 0.227 | (dropped) | (dropped) | 0.419*** | (dropped) | (dropped) |
| (0.16) | (0.01) | |||||
| 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) | ||||
| MSHA Coal District 1 Dummy | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) | (dropped) |
| MSHA Coal District 2 Dummy | 0.005 | -0.003 | 0.003 | -0.005 | -0.002 | -0.007 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 3 Dummy | -0.017 | -0.008 | -0.019* | -0.011 | -0.024** | -0.013 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 4 Dummy | -0.023* | -0.021 | -0.025** | -0.023* | -0.032*** | -0.027* |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 5 Dummy | -0.030*** | -0.026** | -0.031*** | -0.027** | -0.036*** | -0.028** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 6 Dummy | 0.028** | 0.037*** | 0.028*** | 0.035*** | 0.021** | 0.033** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 7 Dummy | 0.009 | -0.002 | 0.008 | -0.003 | 0.002 | -0.006 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| MSHA Coal District 8 Dummy | -0.009 | -0.009 | -0.010 | -0.010 | -0.012 | -0.013 |
| (0.02) | (0.02) | (0.02) | (0.02) | (0.02) | (0.02) | |
| MSHA Coal District 9 Dummy | -0.023 | -0.027 | -0.025* | -0.030 | -0.031** | -0.034* |
| (0.02) | (0.02) | (0.01) | (0.02) | (0.01) | (0.02) | |
| MSHA Coal District 10 Dummy | (dropped) | (dropped) | 0.001 | (dropped) | -0.001 | (dropped) |
| (0.01) | (0.01) | |||||
| MSHA Coal District 11 Dummy | 0.002 | 0.003 | (dropped) | 0.001 | (dropped) | 0.005 |
| (0.01) | (0.02) | (0.02) | (0.02) | |||
| MSHA Coal District 12 Dummy | -0.049*** | -0.033** | -0.050*** | -0.034** | -0.055*** | -0.036** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1995q1 | 0.003 | (dropped) | 0.002 | (dropped) | 0.003 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1995q2 | 0.003 | (dropped) | 0.002 | (dropped) | 0.003 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1995q3 | 0.010 | (dropped) | 0.011 | (dropped) | 0.011 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1995q4 | -0.026*** | (dropped) | -0.026*** | (dropped) | -0.025*** | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1996q1 | -0.016** | (dropped) | -0.015* | (dropped) | -0.015* | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1996q2 | 0.027*** | (dropped) | 0.026*** | (dropped) | 0.027*** | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1996q3 | 0.025*** | (dropped) | 0.025*** | (dropped) | 0.026*** | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1996q4 | -0.006 | (dropped) | -0.007 | (dropped) | -0.007 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1997q1 | -0.005 | (dropped) | -0.002 | (dropped) | -0.002 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1997q2 | 0.037*** | (dropped) | 0.037*** | (dropped) | 0.038*** | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1997q3 | 0.030*** | (dropped) | 0.032*** | (dropped) | 0.033*** | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1997q4 | -0.003 | (dropped) | -0.001 | (dropped) | -0.000 | (dropped) |
| (0.01) | (0.01) | (0.01) | ||||
| Quarter Dummy - 1998q1 | -0.000 | -0.056*** | -0.000 | -0.005 | 0.000 | -0.005 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1998q2 | 0.027*** | -0.030*** | 0.027*** | 0.022** | 0.028*** | 0.021** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1998q3 | 0.032*** | -0.025*** | 0.031*** | 0.025*** | 0.032*** | 0.025*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1998q4 | 0.004 | -0.052*** | 0.004 | -0.001 | 0.004 | -0.002 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1999q1 | 0.006 | -0.049*** | 0.005 | 0.000 | 0.004 | -0.001 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1999q2 | 0.034*** | -0.021*** | 0.035*** | 0.030*** | 0.034*** | 0.029*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1999q3 | 0.037*** | -0.018** | 0.037*** | 0.032*** | 0.036*** | 0.031*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 1999q4 | 0.001 | -0.054*** | 0.001 | -0.004 | 0.000 | -0.005 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2000q1 | 0.007 | -0.047*** | 0.007 | 0.003 | 0.006 | 0.002 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2000q2 | 0.037*** | -0.018** | 0.038*** | 0.033*** | 0.038*** | 0.033*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2000q3 | 0.038*** | -0.017** | 0.040*** | 0.035*** | 0.039*** | 0.034*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2000q4 | 0.012 | -0.043*** | 0.014* | 0.009 | 0.013 | 0.008 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2001q1 | 0.011 | -0.044*** | 0.012 | 0.008 | 0.011 | 0.007 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2001q2 | 0.037*** | -0.018*** | 0.039*** | 0.034*** | 0.039*** | 0.033*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2001q3 | 0.043*** | -0.012* | 0.046*** | 0.041*** | 0.046*** | 0.040*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2001q4 | 0.039*** | -0.015** | 0.039*** | 0.035*** | 0.039*** | 0.035*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2002q1 | 0.044*** | -0.010 | 0.044*** | 0.040*** | 0.044*** | 0.039*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2002q2 | 0.043*** | -0.012 | 0.044*** | 0.039*** | 0.044*** | 0.038*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2002q3 | 0.036*** | -0.020*** | 0.035*** | 0.029*** | 0.034*** | 0.028*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2002q4 | 0.049*** | -0.008 | 0.049*** | 0.043*** | 0.048*** | 0.042*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2003q1 | 0.038*** | -0.016** | 0.041*** | 0.037*** | 0.040*** | 0.035*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2003q2 | 0.046*** | -0.009 | 0.048*** | 0.043*** | 0.047*** | 0.042*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2003q3 | 0.052*** | -0.003 | 0.053*** | 0.048*** | 0.052*** | 0.047*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2003q4 | 0.033*** | -0.022** | 0.033*** | 0.028*** | 0.032*** | 0.027*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2004q1 | 0.033*** | -0.020** | 0.035*** | 0.032*** | 0.034*** | 0.031*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2004q2 | 0.042*** | -0.012* | 0.042*** | 0.038*** | 0.041*** | 0.037*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2004q3 | 0.047*** | -0.007 | 0.046*** | 0.043*** | 0.046*** | 0.042*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2004q4 | 0.037*** | -0.017** | 0.037*** | 0.033*** | 0.036*** | 0.032*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2005q1 | 0.029*** | -0.025*** | 0.029*** | 0.026*** | 0.029*** | 0.025*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2005q2 | 0.036*** | -0.017** | 0.035*** | 0.032*** | 0.035*** | 0.031*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2005q3 | 0.038*** | -0.016** | 0.038*** | 0.034*** | 0.037*** | 0.033*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2005q4 | 0.033*** | -0.021*** | 0.033*** | 0.029*** | 0.033*** | 0.028*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2006q1 | 0.028*** | -0.025*** | 0.030*** | 0.028*** | 0.030*** | 0.027*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2006q2 | 0.028*** | -0.026*** | 0.027*** | 0.023*** | 0.027*** | 0.023*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2006q3 | 0.012 | -0.041*** | 0.014* | 0.012 | 0.014* | 0.012 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2006q4 | 0.013* | -0.042*** | 0.013* | 0.008 | 0.013* | 0.008 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2007q1 | (dropped) | -0.050*** | (dropped) | (dropped) | (dropped) | (dropped) |
| (0.01) | ||||||
| Quarter Dummy - 2007q2 | 0.021*** | -0.031*** | 0.021*** | 0.019*** | 0.021*** | 0.019*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2007q3 | 0.009 | -0.044*** | 0.007 | 0.004 | 0.007 | 0.004 |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2007q4 | 0.037*** | -0.017*** | 0.035*** | 0.031*** | 0.034*** | 0.030*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2008q1 | 0.023*** | -0.032*** | 0.022*** | 0.017** | 0.020*** | 0.015** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2008q2 | 0.029*** | -0.027*** | 0.029*** | 0.024*** | 0.027*** | 0.022*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2008q3 | 0.033*** | -0.023*** | 0.032*** | 0.027*** | 0.030*** | 0.026*** |
| (0.01) | (0.00) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2008q4 | 0.042*** | -0.015*** | 0.040*** | 0.034*** | 0.038*** | 0.033*** |
| (0.01) | (0.00) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2009q1 | 0.034*** | -0.021*** | 0.033*** | 0.028*** | 0.032*** | 0.028*** |
| (0.01) | (0.00) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2009q2 | 0.047*** | -0.009** | 0.045*** | 0.039*** | 0.045*** | 0.039*** |
| (0.01) | (0.00) | (0.01) | (0.01) | (0.01) | (0.01) | |
| Quarter Dummy - 2009q3 | 0.056*** | (dropped) | 0.054*** | 0.048*** | 0.053*** | 0.048*** |
| (0.01) | (0.01) | (0.01) | (0.01) | (0.01) | ||
| Quarter Dummy - 2009q4 | 0.058*** | 0.002 | 0.057*** | 0.050*** | 0.055*** | 0.049*** |
| (0.01) | (0.00) | (0.01) | (0.01) | (0.01) | (0.01) | |
| 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) | |
| 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.