Hello -
I am working with a panel data of n = 23 countries and t = 27 years. I have run an "xtreg y x1... x7 i.year, fe" model, but when I include "robust" standard errors, my variables are no longer statistically significant. I have tried to use vce(cluster country1) and vce(robust) to account for heteroskedasticity and autocorrelation, but that is also leading to surprising results where well established variables are not appearing to be significant.
I would be grateful for any advice or suggestions.
xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(conventional)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(34, 587) = 68.01
corr(u_i, Xb) = 0.8698 Prob > F = 0.0000
-------------------------------------------------------------------------------
ln_emissions | Coefficient Std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .0835744 -0.40 0.686 -.1979338 .1303485
ln_GDP | .6707038 .0623552 10.76 0.000 .5482373 .7931703
ln_urban | -.6823813 .1379903 -4.95 0.000 -.953396 -.4113665
ln_energyi | .2863301 .0567451 5.05 0.000 .174882 .3977783
ln_energyc | .6587665 .1141716 5.77 0.000 .434532 .883001
ln_freight | .0753019 .0154509 4.87 0.000 .044956 .1056477
ln_passenger | .2911854 .0328459 8.87 0.000 .2266756 .3556952
|
year |
1996 | .0212138 .0236724 0.90 0.371 -.0252791 .0677067
1997 | .0225933 .0237727 0.95 0.342 -.0240966 .0692831
1998 | .0375484 .0239838 1.57 0.118 -.0095561 .0846529
1999 | .0229932 .0242705 0.95 0.344 -.0246743 .0706608
2000 | .0058723 .0246496 0.24 0.812 -.0425398 .0542844
2001 | .0277172 .0250404 1.11 0.269 -.0214624 .0768968
2002 | .032074 .0254849 1.26 0.209 -.0179788 .0821267
2003 | .0351375 .0260637 1.35 0.178 -.016052 .0863271
2004 | .0396721 .0268454 1.48 0.140 -.0130525 .0923968
2005 | .0420939 .0276458 1.52 0.128 -.0122029 .0963906
2006 | .045472 .0286576 1.59 0.113 -.0108119 .101756
2007 | .0555367 .0297042 1.87 0.062 -.0028028 .1138762
2008 | .0557996 .0300856 1.85 0.064 -.003289 .1148882
2009 | .0711214 .0294516 2.41 0.016 .013278 .1289647
2010 | .0555851 .0297598 1.87 0.062 -.0028636 .1140337
2011 | .0379912 .0302558 1.26 0.210 -.0214316 .097414
2012 | .0231495 .0305849 0.76 0.449 -.0369197 .0832188
2013 | .0108011 .0310587 0.35 0.728 -.0501985 .0718007
2014 | .0285997 .0319254 0.90 0.371 -.0341021 .0913016
2015 | .0412954 .0326392 1.27 0.206 -.0228084 .1053993
2016 | .0457002 .0329293 1.39 0.166 -.0189734 .1103737
2017 | .0359183 .0338866 1.06 0.290 -.0306354 .1024721
2018 | .0396046 .0348834 1.14 0.257 -.0289068 .108116
2019 | .0416776 .0358788 1.16 0.246 -.0287889 .112144
2020 | .0160818 .0359768 0.45 0.655 -.0545771 .0867406
2021 | .0191024 .0373291 0.51 0.609 -.0542125 .0924173
2022 | .0259837 .0385384 0.67 0.500 -.0497063 .1016736
|
_cons | 2.045922 1.183142 1.73 0.084 -.2777857 4.369629
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
F test that all u_i=0: F(22, 587) = 60.71 Prob > F = 0.0000
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe robust
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(robust)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(cluster country1)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(hc2 country1)
Computing degrees of freedom ...
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(23, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust HC2
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3537916 -0.10 0.925 -.7675115 .6999263
ln_GDP | .6707038 .1853579 3.62 0.002 .286295 1.055113
ln_urban | -.6823813 .42527 -1.60 0.123 -1.564337 .1995746
ln_energyi | .2863301 .129096 2.22 0.037 .0186015 .5540587
ln_energyc | .6587665 .5648875 1.17 0.256 -.5127384 1.830271
ln_freight | .0753019 .0618003 1.22 0.236 -.0528641 .2034678
ln_passenger | .2911854 .1255014 2.32 0.030 .0309115 .5514593
|
year |
1996 | .0212138 .0163743 1.30 0.209 -.0127444 .055172
1997 | .0225933 .0188484 1.20 0.243 -.016496 .0616825
1998 | .0375484 .0290171 1.29 0.209 -.0226295 .0977262
1999 | .0229932 .0326513 0.70 0.489 -.0447213 .0907078
2000 | .0058723 .0363021 0.16 0.873 -.0694137 .0811582
2001 | .0277172 .0395199 0.70 0.490 -.0542421 .1096765
2002 | .032074 .0424947 0.75 0.458 -.0560547 .1202027
2003 | .0351375 .0465707 0.75 0.459 -.0614441 .1317192
2004 | .0396721 .0508121 0.78 0.443 -.0657056 .1450499
2005 | .0420939 .0540982 0.78 0.445 -.0700989 .1542866
2006 | .045472 .0561603 0.81 0.427 -.0709973 .1619413
2007 | .0555367 .0604622 0.92 0.368 -.0698542 .1809276
2008 | .0557996 .0609454 0.92 0.370 -.0705935 .1821926
2009 | .0711214 .05901 1.21 0.241 -.0512579 .1935006
2010 | .0555851 .0582626 0.95 0.350 -.0652441 .1764142
2011 | .0379912 .0626277 0.61 0.550 -.0918907 .1678731
2012 | .0231495 .0677652 0.34 0.736 -.117387 .163686
2013 | .0108011 .071034 0.15 0.881 -.1365143 .1581165
2014 | .0285997 .0773641 0.37 0.715 -.1318437 .1890431
2015 | .0412954 .0769903 0.54 0.597 -.1183727 .2009636
2016 | .0457002 .0762284 0.60 0.555 -.112388 .2037883
2017 | .0359183 .0779478 0.46 0.649 -.1257354 .1975721
2018 | .0396046 .0828428 0.48 0.637 -.1322007 .21141
2019 | .0416776 .0871142 0.48 0.637 -.1389863 .2223414
2020 | .0160818 .0884969 0.18 0.857 -.1674497 .1996132
2021 | .0191024 .0910732 0.21 0.836 -.1697718 .2079767
2022 | .0259837 .0968669 0.27 0.791 -.1749059 .2268733
|
_cons | 2.045922 2.290856 0.89 0.381 -2.705023 6.796866
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
I am working with a panel data of n = 23 countries and t = 27 years. I have run an "xtreg y x1... x7 i.year, fe" model, but when I include "robust" standard errors, my variables are no longer statistically significant. I have tried to use vce(cluster country1) and vce(robust) to account for heteroskedasticity and autocorrelation, but that is also leading to surprising results where well established variables are not appearing to be significant.
I would be grateful for any advice or suggestions.
xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(conventional)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(34, 587) = 68.01
corr(u_i, Xb) = 0.8698 Prob > F = 0.0000
-------------------------------------------------------------------------------
ln_emissions | Coefficient Std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .0835744 -0.40 0.686 -.1979338 .1303485
ln_GDP | .6707038 .0623552 10.76 0.000 .5482373 .7931703
ln_urban | -.6823813 .1379903 -4.95 0.000 -.953396 -.4113665
ln_energyi | .2863301 .0567451 5.05 0.000 .174882 .3977783
ln_energyc | .6587665 .1141716 5.77 0.000 .434532 .883001
ln_freight | .0753019 .0154509 4.87 0.000 .044956 .1056477
ln_passenger | .2911854 .0328459 8.87 0.000 .2266756 .3556952
|
year |
1996 | .0212138 .0236724 0.90 0.371 -.0252791 .0677067
1997 | .0225933 .0237727 0.95 0.342 -.0240966 .0692831
1998 | .0375484 .0239838 1.57 0.118 -.0095561 .0846529
1999 | .0229932 .0242705 0.95 0.344 -.0246743 .0706608
2000 | .0058723 .0246496 0.24 0.812 -.0425398 .0542844
2001 | .0277172 .0250404 1.11 0.269 -.0214624 .0768968
2002 | .032074 .0254849 1.26 0.209 -.0179788 .0821267
2003 | .0351375 .0260637 1.35 0.178 -.016052 .0863271
2004 | .0396721 .0268454 1.48 0.140 -.0130525 .0923968
2005 | .0420939 .0276458 1.52 0.128 -.0122029 .0963906
2006 | .045472 .0286576 1.59 0.113 -.0108119 .101756
2007 | .0555367 .0297042 1.87 0.062 -.0028028 .1138762
2008 | .0557996 .0300856 1.85 0.064 -.003289 .1148882
2009 | .0711214 .0294516 2.41 0.016 .013278 .1289647
2010 | .0555851 .0297598 1.87 0.062 -.0028636 .1140337
2011 | .0379912 .0302558 1.26 0.210 -.0214316 .097414
2012 | .0231495 .0305849 0.76 0.449 -.0369197 .0832188
2013 | .0108011 .0310587 0.35 0.728 -.0501985 .0718007
2014 | .0285997 .0319254 0.90 0.371 -.0341021 .0913016
2015 | .0412954 .0326392 1.27 0.206 -.0228084 .1053993
2016 | .0457002 .0329293 1.39 0.166 -.0189734 .1103737
2017 | .0359183 .0338866 1.06 0.290 -.0306354 .1024721
2018 | .0396046 .0348834 1.14 0.257 -.0289068 .108116
2019 | .0416776 .0358788 1.16 0.246 -.0287889 .112144
2020 | .0160818 .0359768 0.45 0.655 -.0545771 .0867406
2021 | .0191024 .0373291 0.51 0.609 -.0542125 .0924173
2022 | .0259837 .0385384 0.67 0.500 -.0497063 .1016736
|
_cons | 2.045922 1.183142 1.73 0.084 -.2777857 4.369629
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
F test that all u_i=0: F(22, 587) = 60.71 Prob > F = 0.0000
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe robust
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(robust)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(cluster country1)
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(22, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3019467 -0.11 0.912 -.6599918 .5924066
ln_GDP | .6707038 .1556004 4.31 0.000 .3480084 .9933992
ln_urban | -.6823813 .36935 -1.85 0.078 -1.448366 .0836038
ln_energyi | .2863301 .112803 2.54 0.019 .052391 .5202693
ln_energyc | .6587665 .4708758 1.40 0.176 -.3177701 1.635303
ln_freight | .0753019 .054206 1.39 0.179 -.0371145 .1877183
ln_passenger | .2911854 .109376 2.66 0.014 .0643534 .5180173
|
year |
1996 | .0212138 .0166292 1.28 0.215 -.013273 .0557006
1997 | .0225933 .0190104 1.19 0.247 -.016832 .0620185
1998 | .0375484 .0290602 1.29 0.210 -.0227187 .0978155
1999 | .0229932 .0326031 0.71 0.488 -.0446214 .0906079
2000 | .0058723 .0349706 0.17 0.868 -.0666522 .0783968
2001 | .0277172 .0379029 0.73 0.472 -.0508885 .1063229
2002 | .032074 .0404138 0.79 0.436 -.0517392 .1158872
2003 | .0351375 .0445973 0.79 0.439 -.0573516 .1276267
2004 | .0396721 .0483981 0.82 0.421 -.0606994 .1400437
2005 | .0420939 .0510843 0.82 0.419 -.0638486 .1480363
2006 | .045472 .0521962 0.87 0.393 -.0627762 .1537203
2007 | .0555367 .0554875 1.00 0.328 -.0595373 .1706107
2008 | .0557996 .0553746 1.01 0.325 -.0590403 .1706394
2009 | .0711214 .0534839 1.33 0.197 -.0397975 .1820403
2010 | .0555851 .0524591 1.06 0.301 -.0532085 .1643786
2011 | .0379912 .05559 0.68 0.501 -.0772954 .1532778
2012 | .0231495 .0602469 0.38 0.704 -.101795 .148094
2013 | .0108011 .0630046 0.17 0.865 -.1198625 .1414647
2014 | .0285997 .0688644 0.42 0.682 -.1142163 .1714158
2015 | .0412954 .0682816 0.60 0.552 -.1003119 .1829028
2016 | .0457002 .0678447 0.67 0.508 -.0950012 .1864015
2017 | .0359183 .0690491 0.52 0.608 -.1072808 .1791174
2018 | .0396046 .0729832 0.54 0.593 -.1117534 .1909626
2019 | .0416776 .0764724 0.55 0.591 -.1169164 .2002716
2020 | .0160818 .077312 0.21 0.837 -.1442535 .176417
2021 | .0191024 .0787538 0.24 0.811 -.144223 .1824279
2022 | .0259837 .083765 0.31 0.759 -.1477344 .1997017
|
_cons | 2.045922 1.992457 1.03 0.316 -2.086181 6.178025
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
.
. xtreg ln_emissions ln_population ln_GDP ln_urban ln_energyi ln_energyc ln_freigh
> t ln_passenger i.year, fe vce(hc2 country1)
Computing degrees of freedom ...
Fixed-effects (within) regression Number of obs = 644
Group variable: country1 Number of groups = 23
R-squared: Obs per group:
Within = 0.7975 min = 28
Between = 0.9367 avg = 28.0
Overall = 0.8924 max = 28
F(23, 22) = .
corr(u_i, Xb) = 0.8698 Prob > F = .
(Std. err. adjusted for 23 clusters in country1)
-------------------------------------------------------------------------------
| Robust HC2
ln_emissions | Coefficient std. err. t P>|t| [95% conf. interval]
--------------+----------------------------------------------------------------
ln_population | -.0337926 .3537916 -0.10 0.925 -.7675115 .6999263
ln_GDP | .6707038 .1853579 3.62 0.002 .286295 1.055113
ln_urban | -.6823813 .42527 -1.60 0.123 -1.564337 .1995746
ln_energyi | .2863301 .129096 2.22 0.037 .0186015 .5540587
ln_energyc | .6587665 .5648875 1.17 0.256 -.5127384 1.830271
ln_freight | .0753019 .0618003 1.22 0.236 -.0528641 .2034678
ln_passenger | .2911854 .1255014 2.32 0.030 .0309115 .5514593
|
year |
1996 | .0212138 .0163743 1.30 0.209 -.0127444 .055172
1997 | .0225933 .0188484 1.20 0.243 -.016496 .0616825
1998 | .0375484 .0290171 1.29 0.209 -.0226295 .0977262
1999 | .0229932 .0326513 0.70 0.489 -.0447213 .0907078
2000 | .0058723 .0363021 0.16 0.873 -.0694137 .0811582
2001 | .0277172 .0395199 0.70 0.490 -.0542421 .1096765
2002 | .032074 .0424947 0.75 0.458 -.0560547 .1202027
2003 | .0351375 .0465707 0.75 0.459 -.0614441 .1317192
2004 | .0396721 .0508121 0.78 0.443 -.0657056 .1450499
2005 | .0420939 .0540982 0.78 0.445 -.0700989 .1542866
2006 | .045472 .0561603 0.81 0.427 -.0709973 .1619413
2007 | .0555367 .0604622 0.92 0.368 -.0698542 .1809276
2008 | .0557996 .0609454 0.92 0.370 -.0705935 .1821926
2009 | .0711214 .05901 1.21 0.241 -.0512579 .1935006
2010 | .0555851 .0582626 0.95 0.350 -.0652441 .1764142
2011 | .0379912 .0626277 0.61 0.550 -.0918907 .1678731
2012 | .0231495 .0677652 0.34 0.736 -.117387 .163686
2013 | .0108011 .071034 0.15 0.881 -.1365143 .1581165
2014 | .0285997 .0773641 0.37 0.715 -.1318437 .1890431
2015 | .0412954 .0769903 0.54 0.597 -.1183727 .2009636
2016 | .0457002 .0762284 0.60 0.555 -.112388 .2037883
2017 | .0359183 .0779478 0.46 0.649 -.1257354 .1975721
2018 | .0396046 .0828428 0.48 0.637 -.1322007 .21141
2019 | .0416776 .0871142 0.48 0.637 -.1389863 .2223414
2020 | .0160818 .0884969 0.18 0.857 -.1674497 .1996132
2021 | .0191024 .0910732 0.21 0.836 -.1697718 .2079767
2022 | .0259837 .0968669 0.27 0.791 -.1749059 .2268733
|
_cons | 2.045922 2.290856 0.89 0.381 -2.705023 6.796866
--------------+----------------------------------------------------------------
sigma_u | .79042426
sigma_e | .07992255
rho | .98987953 (fraction of variance due to u_i)
-------------------------------------------------------------------------------
Comment