xtreg vs. LSDV

[Felix Stips]

Dear statalists,

I hope this question is not an oldie. Surprisingly, to me, i have not found any discussion on this in the forum posts. I tried to estimate threeway fixed effects via the xtreg and interaction expansion command. My understanding was that, even though they use different calculations, they should imply the same.

However i get different results for the constant and the fe's

reg ln_fdi_stock $distcontrolsG i.importer i.exporter i.yr
xtreg ln_fdi_stock $distcontrolsG i.yr i.exporter, fe i(importer)

importer |
2 | 1.884145 .196537 9.59 0.000 1.498929 2.269362
3 | 3.169294 .2131197 14.87 0.000 2.751575 3.587013
4 | 3.461649 .1449207 23.89 0.000 3.177602 3.745696
5 | -.4018992 .1574931 -2.55 0.011 -.7105888 -.0932095
6 | 5.318759 .153963 34.55 0.000 5.016988 5.620529
7 | 2.361348 .1466429 16.10 0.000 2.073925 2.648771
8 | 1.028668 .1640239 6.27 0.000 .7071779 1.350158
9 | 1.299722 .1537005 8.46 0.000 .9984658 1.600978
10 | -.1517205 .1644365 -0.92 0.356 -.4740194 .1705783
11 | 3.332578 .1442507 23.10 0.000 3.049844 3.615312
12 | -.1590171 .316898 -0.50 0.616 -.7801434 .4621091
13 | 1.310839 .1858917 7.05 0.000 .9464882 1.675191
14 | .2286898 .160598 1.42 0.154 -.0860854 .5434651
15 | .3745796 .1999689 1.87 0.061 -.0173634 .7665227
....
_cons | 6.007166 .4020739 14.94 0.000 5.219093 6.795238


2 | .6924308 .4718152 1.47 0.142 -.2323363 1.617198
3 | 1.261118 .4470196 2.82 0.005 .384951 2.137285
4 | 3.3261 .4298435 7.74 0.000 2.483598 4.168602
5 | 4.476361 .3855753 11.61 0.000 3.720626 5.232096
6 | 1.635004 .4659014 3.51 0.000 .7218282 2.54818
7 | 6.781577 .3739167 18.14 0.000 6.048693 7.514461
8 | 5.391401 .3730204 14.45 0.000 4.660273 6.122528
9 | 1.816172 .3962854 4.58 0.000 1.039445 2.592899
10 | 5.098008 .3776053 13.50 0.000 4.357894 5.838122
11 | 3.316414 .3946715 8.40 0.000 2.54285 4.089978
12 | 1.108172 .414883 2.67 0.008 .2949931 1.921351
13 | 5.116808 .4005912 12.77 0.000 4.331641 5.901974
14 | .4545641 .3969522 1.15 0.252 -.3234701 1.232598
15 | 5.665018 .3720416 15.23 0.000 4.935809 6.394227
....
_cons | 8.455639 .3865197 21.88 0.000 7.698052 9.213225

Does anybody know what i might be missing here? If You need more output, please let me know.

Many Thanks,
Felix Stips

[daniel klein]

Felix,

you are correct, the two ways of estimating this model, de-meaning/within-estimator/fixed-effects and least square dummy variable estimator (LSDV), result in the same estimates. There are several things unclear with your post, which might explain your confusion.

First, you wonder about differences in the constant terms. Note that, there is no constant in a fixed-effects (de-meaned) model, as the constant is wiped out by the de-meaning. What Stata reports is as a constant, is basically the mean average value for the fixed effects (see here).

You then claim to observe differences in the fixed-effects and show us coefficients(?) for importer - but this is the variable identifying your panel units, so there cannot be any estimates for them in fixed-effects (de-meaned) model.

Hope this gives you an idea. If not, please provide the full syntax (including definitions of macros) along with the full output (probably using estimates table.

Best
Daniel

[Felix Stips]

Hi Daniel,

Thank You for Your quick reply. I use threeway fixed effects. So the xtreg version of the command (at least in theory) demeans over importer and then when i later use predict, xb i can have a "predict" (or rather get fitted values) that includes exporter and year fixed effects, but not the importer fixed effects. that was my original reasoning. I thought this could be easier than doing reg i.importer .. and then compute "predicting" by hand. And since the coefficients for the controls should be the same, why not also the additional dummies? I posted the code and output below (with a couple of dummies not posted, but i guessed they dont matter that much).

Yes, I read this documentation. I guess i understood the formula (5)
_ = _ = _ _ = y_it - y_i + y = a + (x_it - x_i + x)b + (e_it - e_i + v) + e seeing a as a "traditional" constant. Ok, so the two terms do not represent the same in the two approaches. But when You use "predict", they are still used in the same way y= _b[_a] + ln_dist*_b[_ln_dist] ... + _b[_Iexportery_1]* _Iexportery_1 + ...
Are these fitted y's the same in both approaches? If in my case a is smaller for LSDV than for xtreg is this then compensated by higher values of the dummy coeffcients? Hope my doubts are clearer now.

global distcontrolsG ln_dist contig smctry both_landlocked /* geography */
reg ln_fdi_stock $distcontrolsG i.importer i.exporter i.yr
xtset importer
       panel variable:  importer (unbalanced)
xtreg ln_fdi_stock $distcontrolsG i.yr i.exporter, fe i(importer)


--------------------------------------------
                      (1)             (2)  
             ln_fdi_stock    ln_fdi_stock  
--------------------------------------------
ln_dist            -1.193***       -1.193***
                 (0.0138)        (0.0138)  

contig              0.681***        0.681***
                 (0.0435)        (0.0435)  

smctry              0.820***        0.820***
                 (0.0693)        (0.0693)  

both_landl~d       -1.069**        -1.727  
                  (0.442)         (1.830)  

1.importer              0                  
                      (.)                  

2.importer          1.878***                
                  (0.197)                  

3.importer          3.162***                
                  (0.213)                  

4.importer          3.460***                
                  (0.145)                  

5.importer          0.630                  
                  (0.469)                  

6.importer          5.315***                
                  (0.154)                  

7.importer          3.392***                
                  (0.466)                  

8.importer          2.059***                
                  (0.469)                  

9.importer          1.299***                
                  (0.154)                  

10.importer        -0.146                  
                  (0.164)                  

11.importer         3.334***                
                  (0.144)                  

12.importer        -0.152                  
                  (0.317)                  

13.importer         2.337***                
                  (0.479)                  

14.importer         0.239                  
                  (0.161)                  

15.importer         1.383***                
                  (0.485)                  

16.importer         4.869***                
                  (0.149)                  

17.importer         1.604***                
                  (0.138)                  

18.importer         2.714***                
                  (0.569)                  

19.importer         0.782***                
                  (0.157)                  

20.importer         0.564**                
                  (0.235)                  

21.importer         4.327***                
                  (0.145)                  

22.importer         4.029***                
                  (0.157)                  

23.importer         4.972***                
                  (0.146)                  

24.importer         2.840***                
                  (0.183)                  

25.importer         1.683***                
                  (0.255)                  

26.importer         1.366***                
                  (0.170)                  

27.importer         0.602***                
                  (0.146)                  

28.importer         2.798***                
                  (0.464)                  

29.importer         1.126***                
                  (0.214)                  

30.importer         0.981***                
                  (0.301)                  

31.importer         3.231***                
                  (0.141)                  

32.importer         1.512***                
                  (0.216)                  

33.importer         1.914***                
                  (0.197)                  

34.importer         2.185***                
                  (0.170)                  

35.importer         1.313***                
                  (0.163)                  

36.importer         0.703***                
                  (0.146)                  

37.importer         1.191**                
                  (0.522)                  

38.importer         1.754***                
                  (0.151)                  

39.importer         4.486***                
                  (0.135)                  

40.importer         2.203***                
                  (0.245)                  

41.importer         1.004***                
                  (0.177)                  

42.importer         3.884***                
                  (0.140)                  

43.importer         0.876***                
                  (0.188)                  

44.importer         1.661***                
                  (0.154)                  

45.importer         1.417***                
                  (0.198)                  

46.importer         0.777***                
                  (0.283)                  

47.importer       -0.0534                  
                  (0.616)                  

48.importer         1.085***                
                  (0.208)                  

49.importer         4.333***                
                  (0.155)                  

50.importer         3.019***                
                  (0.465)                  

51.importer        -0.120                  
                  (0.179)                  

52.importer         3.019***                
                  (0.149)                  

53.importer         3.340***                
                  (0.160)                  

54.importer         1.010***                
                  (0.191)                  

55.importer         1.485***                
                  (0.294)                  

56.importer         3.215***                
                  (0.155)                  

57.importer         1.575***                
                  (0.160)                  

58.importer         2.803***                
                  (0.138)                  

59.importer         0.968***                
                  (0.274)                  

60.importer         3.500***                
                  (0.150)                  

61.importer         0.559***                
                  (0.191)                  

62.importer         3.321***                
                  (0.465)                  

63.importer         1.037***                
                  (0.187)                  

64.importer         0.165                  
                  (0.207)                  

65.importer         0.467                  
                  (0.478)                  

66.importer         0.671***                
                  (0.145)                  

67.importer         0.112                  
                  (0.217)                  

68.importer         0.261                  
                  (0.552)                  

69.importer         2.531***                
                  (0.195)                  

70.importer         1.563***                
                  (0.198)                  

71.importer         0.746***                
                  (0.144)                  

72.importer         0.546***                
                  (0.191)                  

73.importer         1.690***                
                  (0.481)                  

74.importer         3.544***                
                  (0.162)                  

75.importer         1.153**                
                  (0.495)                  

76.importer         2.570***                
                  (0.158)                  

77.importer         3.700***                
                  (0.150)                  

78.importer         1.855***                
                  (0.467)                  

79.importer         2.381***                
                  (0.165)                  

80.importer         1.468***                
                  (0.196)                  

81.importer         1.502***                
                  (0.249)                  

82.importer         0.475**                
                  (0.240)                  

83.importer        0.0481                  
                  (0.492)                  

84.importer         4.017***                
                  (0.139)                  

85.importer         3.547***                
                  (0.166)                  

86.importer         0.251                  
                  (0.254)                  

87.importer         2.330***                
                  (0.170)                  

88.importer         2.164***                
                  (0.141)                  

89.importer         1.694***                
                  (0.171)                  

90.importer         2.059***                
                  (0.155)                  

91.importer         2.800***                
                  (0.156)                  

92.importer         0.974***                
                  (0.197)                  

93.importer         1.867***                
                  (0.473)                  

94.importer         2.329***                
                  (0.151)                  

95.importer         1.983***                
                  (0.152)                  

96.importer         2.655***                
                  (0.141)                  

97.importer         2.221***                
                  (0.145)                  

98.importer         2.049***                
                  (0.197)                  

99.importer         3.093***                
                  (0.141)                  

100.importer        3.747***                
                  (0.137)                  

101.importer        2.004***                
                  (0.141)                  

102.importer        3.240***                
                  (0.143)                  

103.importer        0.386                  
                  (0.545)                  

104.importer        3.068***                
                  (0.158)                  

105.importer        0.289                  
                  (0.210)                  

106.importer        1.003***                
                  (0.157)                  

107.importer       -0.906***                
                  (0.345)                  

108.importer        5.140***                
                  (0.150)                  

109.importer        2.223***                
                  (0.467)                  

110.importer        0.205                  
                  (0.149)                  

111.importer        3.854***                
                  (0.140)                  

112.importer        4.311***                
                  (0.146)                  

113.importer        1.185***                
                  (0.216)                  

114.importer        1.766***                
                  (0.276)                  

115.importer        1.633***                
                  (0.542)                  

116.importer        3.047***                
                  (0.155)                  

117.importer        4.492***                
                  (0.466)                  

118.importer      -0.0841                  
                  (0.232)                  

119.importer        1.758***                
                  (0.529)                  

120.importer        3.341***                
                  (0.149)                  

121.importer        0.873*                  
                  (0.468)                  

122.importer       -0.391                  
                  (0.274)                  

123.importer        2.153***                
                  (0.222)                  

124.importer        0.127                  
                  (0.198)                  

125.importer        2.588***                
                  (0.141)                  

126.importer        2.526***                
                  (0.480)                  

127.importer        1.792***                
                  (0.138)                  

128.importer        3.011***                
                  (0.163)                  

129.importer        4.602***                
                  (0.142)                  

130.importer        1.488***                
                  (0.145)                  

131.importer        5.797***                
                  (0.139)                  

132.importer        1.913***                
                  (0.178)                  

133.importer        2.491***                
                  (0.497)                  

134.importer        2.911***                
                  (0.166)                  

135.importer        2.608***                
                  (0.173)                  

136.importer        2.026***                
                  (0.250)                  

137.importer        2.325***                
                  (0.474)                  

138.importer        2.115***                
                  (0.511)                  

1.exporter              0               0  
                      (.)             (.)  

2.exporter         -0.346          -1.004  
                  (0.387)         (1.818)  

3.exporter          0.205          -0.453  
                  (0.356)         (1.812)  

4.exporter          2.268***        1.610  
                  (0.334)         (1.807)  

5.exporter          3.425***        2.767  
                  (0.275)         (1.797)  

6.exporter          1.645***        1.645***
                  (0.466)         (0.466)  

7.exporter          5.727***        5.069***
                  (0.259)         (1.795)  

8.exporter          5.367***        5.367***
                  (0.373)         (0.373)  

9.exporter          1.790***        1.790***
                  (0.396)         (0.396)  

10.exporter         4.047***        3.389*  
                  (0.264)         (1.796)  

11.exporter         2.264***        1.606  
                  (0.288)         (1.799)  

12.exporter        0.0559          -0.602  
                  (0.316)         (1.804)  

13.exporter         4.064***        3.406*  
                  (0.296)         (1.801)  

14.exporter        -0.591**        -1.249  
                  (0.291)         (1.800)  

15.exporter         4.616***        3.958**
                  (0.256)         (1.794)  

16.exporter         3.383***        2.725  
                  (0.287)         (1.799)  

17.exporter         0.383          -0.275  
                  (0.559)         (1.862)  

18.exporter         0.765           0.765  
                  (1.830)         (1.830)  

19.exporter         0.499           0.499  
                  (0.481)         (0.481)  

20.exporter         0.135          -0.523  
                  (0.340)         (1.808)  

21.exporter         2.350***        2.350***
                  (0.447)         (0.447)  

22.exporter         4.370***        3.712**
                  (0.260)         (1.795)  

23.exporter         0.390          -0.268  
                  (0.375)         (1.815)  

24.exporter        0.0149          -0.643  
                  (0.263)         (1.796)  

25.exporter         0.775           0.775  
                  (0.637)         (0.637)  

26.exporter        -0.419          -0.419  
                  (1.098)         (1.098)  

27.exporter        -1.906***       -2.564  
                  (0.465)         (1.836)  

28.exporter         1.668***        1.010  
                  (0.472)         (1.838)  

29.exporter         6.014***        5.356***
                  (0.255)         (1.794)  

30.exporter         0.531          -0.127  
                  (0.648)         (1.889)  

31.exporter         1.006           1.006  
                  (0.771)         (0.771)  

32.exporter         1.414**         1.414**
                  (0.604)         (0.604)  

33.exporter         3.396***        2.738  
                  (0.270)         (1.796)  

34.exporter         4.600***        3.942**
                  (0.253)         (1.794)  

35.exporter         2.694***        2.036  
                  (0.290)         (1.800)  

36.exporter         0.949*          0.291  
                  (0.576)         (1.867)  

37.exporter         1.581***        0.923  
                  (0.512)         (1.849)  

38.exporter         1.354***        0.696  
                  (0.302)         (1.801)  

39.exporter         0.530**        -0.128  
                  (0.266)         (1.796)  

40.exporter         3.585***        2.927  
                  (0.257)         (1.795)  

41.exporter         2.277***        2.277***
                  (0.375)         (0.375)  

42.exporter         1.458***        0.800  
                  (0.358)         (1.812)  

43.exporter         1.169**         0.511  
                  (0.556)         (1.861)  

44.exporter         0.965*          0.307  
                  (0.502)         (1.846)  

45.exporter         4.491***        3.833**
                  (0.254)         (1.794)  

47.exporter         1.197***        0.539  
                  (0.359)         (1.812)  

48.exporter         1.317***        0.659  
                  (0.312)         (1.803)  

49.exporter         1.978***        1.320  
                  (0.282)         (1.798)  

50.exporter         0.444          -0.214  
                  (0.398)         (1.820)  

51.exporter        -0.749          -1.407  
                  (1.811)         (2.537)  

52.exporter         0.323          -0.335  
                  (1.296)         (2.199)  

53.exporter         0.509*         -0.149  
                  (0.266)         (1.796)  

54.exporter         1.648***        1.648***
                  (0.635)         (0.635)  

55.exporter        -0.938          -1.596  
                  (1.292)         (2.196)  

56.exporter         3.912***        3.254*  
                  (0.257)         (1.795)  

57.exporter         6.314***        5.656***
                  (0.253)         (1.794)  

58.exporter         0.167          -0.491  
                  (0.557)         (1.861)  

59.exporter         1.400***        0.742  
                  (0.420)         (1.825)  

60.exporter         2.177           1.519  
                  (1.810)         (2.536)  

61.exporter         0.173          -0.485  
                  (0.342)         (1.809)  

62.exporter         6.141***        5.483***
                  (0.253)         (1.794)  

63.exporter         1.280***        0.622  
                  (0.374)         (1.815)  

64.exporter         2.488***        1.830  
                  (0.263)         (1.795)  

65.exporter         0.683*         0.0254  
                  (0.372)         (1.815)  

66.exporter         1.887***        1.229  
                  (0.682)         (1.903)  

67.exporter        -0.838          -1.496  
                  (0.725)         (1.915)  

68.exporter         2.259*          1.601  
                  (1.293)         (2.197)  

69.exporter        -1.974***       -2.632  
                  (0.596)         (1.873)  

70.exporter        -1.001**        -1.659  
                  (0.389)         (1.818)  

71.exporter         5.023***        4.365**
                  (0.260)         (1.795)  

72.exporter         2.760***        2.760***
                  (0.375)         (0.375)  

73.exporter         2.290***        1.632  
                  (0.261)         (1.795)  

74.exporter         3.159***        2.501  
                  (0.258)         (1.795)  

75.exporter         2.633***        1.975  
                  (0.274)         (1.797)  

76.exporter         2.025***        1.367  
                  (0.283)         (1.799)  

77.exporter         0.834**         0.176  
                  (0.347)         (1.810)  

78.exporter         4.417***        3.759**
                  (0.259)         (1.795)  

79.exporter         2.737***        2.079  
                  (0.257)         (1.795)  

80.exporter         4.911***        4.253**
                  (0.254)         (1.794)  

81.exporter         0.718*         0.0599  
                  (0.407)         (1.822)  

82.exporter         6.686***        6.028***
                  (0.256)         (1.794)  

83.exporter         1.219***        0.561  
                  (0.300)         (1.801)  

84.exporter         3.037***        3.037***
                  (0.382)         (0.382)  

85.exporter         1.738***        1.080  
                  (0.310)         (1.803)  

86.exporter         3.540***        2.882  
                  (0.272)         (1.797)  

87.exporter         1.452***        1.452***
                  (0.443)         (0.443)  

88.exporter        -0.573          -0.573  
                  (0.492)         (0.492)  

89.exporter         0.502*         -0.156  
                  (0.268)         (1.796)  

90.exporter         2.484***        1.826  
                  (0.278)         (1.798)  

91.exporter         1.346**         1.346**
                  (0.553)         (0.553)  

92.exporter         2.469***        1.811  
                  (0.282)         (1.798)  

93.exporter         2.320***        1.662  
                  (0.301)         (1.801)  

94.exporter         0.393          -0.265  
                  (0.270)         (1.796)  

95.exporter         6.668***        6.668***
                  (0.373)         (0.373)  

96.exporter         1.478***        0.820  
                  (0.332)         (1.807)  

97.exporter         0.831           0.173  
                  (0.526)         (1.853)  

98.exporter         1.685***        1.685***
                  (0.465)         (0.465)  

99.exporter         4.207***        3.549**
                  (0.263)         (1.795)  

100.exporter        1.552***        0.894  
                  (0.541)         (1.857)  

101.exporter        1.424***        1.424***
                  (0.532)         (0.532)  

102.exporter        2.948***        2.290  
                  (0.274)         (1.797)  

103.exporter        0.144          -0.514  
                  (0.465)         (1.836)  

104.exporter        4.008***        3.350*  
                  (0.265)         (1.796)  

105.exporter        4.339***        3.681**
                  (0.270)         (1.796)  

106.exporter       -0.968          -1.626  
                  (1.293)         (2.197)  

107.exporter        1.096*          1.096*  
                  (0.654)         (0.654)  

108.exporter        1.326***        0.668  
                  (0.272)         (1.797)  

109.exporter        0.729*         0.0708  
                  (0.386)         (1.817)  

135.exporter       -1.738**        -1.738**
                  (0.776)         (0.776)  

136.exporter        1.394**         0.736  
                  (0.574)         (1.867)  

137.exporter        2.853***        2.195  
                  (0.368)         (1.814)  

138.exporter        2.996***        2.338  
                  (0.344)         (1.809)  

139.exporter        0.658               0  
                  (1.810)             (.)  

140.exporter        2.897***        2.239  
                  (0.269)         (1.796)  

141.exporter        1.056***        0.398  
                  (0.393)         (1.819)  

142.exporter        0.195          -0.463  
                  (0.295)         (1.800)  

143.exporter        0.364          -0.294  
                  (0.556)         (1.861)  

144.exporter        5.525***        4.867***
                  (0.259)         (1.795)  

145.exporter        1.298***        1.298***
                  (0.382)         (0.382)  

146.exporter        0.609**       -0.0490  
                  (0.260)         (1.795)  

148.exporter        0.463          -0.195  
                  (0.556)         (1.862)  

149.exporter        4.084***        3.426*  
                  (0.257)         (1.795)  

150.exporter        5.514***        4.856***
                  (0.257)         (1.795)  

151.exporter        0.720**        0.0622  
                  (0.331)         (1.807)  

152.exporter        0.785*          0.127  
                  (0.442)         (1.831)  

153.exporter        1.264***        0.606  
                  (0.481)         (1.840)  

154.exporter        2.304***        2.304***
                  (0.458)         (0.458)  

155.exporter        5.125***        4.467**
                  (0.256)         (1.794)  

156.exporter        7.039***        7.039***
                  (0.371)         (0.371)  

157.exporter        0.800**         0.142  
                  (0.325)         (1.806)  

158.exporter        1.101*          1.101*  
                  (0.655)         (0.655)  

159.exporter        2.815***        2.157  
                  (0.263)         (1.796)  

160.exporter       -0.396          -0.396  
                  (0.402)         (0.402)  

161.exporter        1.887***        1.229  
                  (0.433)         (1.828)  

162.exporter        0.863           0.205  
                  (1.293)         (2.197)  

163.exporter        2.205***        1.547  
                  (0.346)         (1.810)  

164.exporter        0.990***        0.332  
                  (0.363)         (1.813)  

165.exporter        2.090***        1.432  
                  (0.256)         (1.795)  

166.exporter        0.960**         0.960**
                  (0.456)         (0.456)  

167.exporter        0.619**       -0.0390  
                  (0.270)         (1.797)  

168.exporter        3.705***        3.047*  
                  (0.264)         (1.796)  

169.exporter        7.008***        6.350***
                  (0.254)         (1.794)  

170.exporter        1.385***        0.727  
                  (0.378)         (1.816)  

171.exporter        7.783***        7.125***
                  (0.252)         (1.794)  

172.exporter        3.074***        2.416  
                  (0.282)         (1.798)  

173.exporter        2.312***        2.312***
                  (0.425)         (0.425)  

174.exporter        1.693***        1.035  
                  (0.359)         (1.812)  

175.exporter        2.937***        2.279  
                  (0.286)         (1.799)  

176.exporter        1.214***        0.556  
                  (0.294)         (1.800)  

177.exporter            0          -0.658  
                      (.)         (1.810)  

178.exporter        1.736***        1.736***
                  (0.432)         (0.432)  

179.exporter        1.899***        1.899***
                  (0.449)         (0.449)  

1.yr                    0               0  
                      (.)             (.)  

2.yr                0.153***        0.153***
                 (0.0500)        (0.0500)  

3.yr                0.312***        0.312***
                 (0.0494)        (0.0494)  

4.yr                0.433***        0.433***
                 (0.0484)        (0.0484)  

5.yr                0.520***        0.520***
                 (0.0479)        (0.0479)  

6.yr                0.779***        0.779***
                 (0.0474)        (0.0474)  

7.yr                1.024***        1.024***
                 (0.0466)        (0.0466)  

8.yr                1.130***        1.130***
                 (0.0467)        (0.0467)  

9.yr                1.255***        1.255***
                 (0.0453)        (0.0453)  

10.yr               1.308***        1.308***
                 (0.0448)        (0.0448)  

11.yr               1.410***        1.410***
                 (0.0447)        (0.0447)  

12.yr               1.464***        1.464***
                 (0.0451)        (0.0451)  

_cons               7.051***        10.41***
                  (0.296)         (2.064)  
--------------------------------------------
N                   42893           42893  
--------------------------------------------
Standard errors in parentheses
* p<.10, ** p<.05, *** p<.01

[Sebastian Kripfganz]

I am not sure if I am understanding your data structure. It seems to me that you are trying to estimate some kind of trade gravity model. How do you classify importers and exporters? They cannot be mutually exclusive because xtreg only uses those observations with a non-missing value for your panel identifier variable, importer, and would consequently not report any coefficients for your exporter dummies. But if they are not mutually exclusive, you will have a collinearity problem among your dummy variables, which also becomes clear from your output (139.exporter is omitted by xtreg, and 177.exporter is omitted by reg). The simple fact that both commands omitted different dummies already explains the differences in all your dummy coefficients. However, without knowing anything about your data, in particular the construction of the variables importer and exporter, we cannot give any further advice here. Are these dummies even constant over time?