Good evening, everyone!

The following is a snippet of my database( I have data of Brazil's exports and imports flow with 122 countries, from 2009 to 2014):

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str3(ID_EXP ID_IMP) int(ID_NUM ANO) double(EXP_NRB DIST SCO_EXP SCO_IMP) byte(FRO LIN COL)
"BRA" "AGO"  1 2009  152903849 6391.615 .6991869918699187   .8211382113821139 0 1 0
"BRA" "AGO"  1 2010   60699279 6391.615 .4796747967479675   .7317073170731707 0 1 0
"BRA" "AGO"  1 2011   61883975 6391.615 .5934959349593496   .5528455284552846 0 1 0
"BRA" "AGO"  1 2012   64203369 6391.615 .3821138211382114   .5528455284552846 0 1 0
"BRA" "AGO"  1 2013   75264517 6391.615 .3821138211382114   .8373983739837398 0 1 0
"BRA" "AGO"  1 2014   85859091 6391.615 .2845528455284553   .4959349593495935 0 1 0
"BRA" "ALB"  2 2009      40668 9313.151 .6991869918699187   .8943089430894309 0 0 0
"BRA" "ALB"  2 2010      64360 9313.151 .4796747967479675    .959349593495935 0 0 0
"BRA" "ALB"  2 2011       1467 9313.151 .5934959349593496   .5447154471544715 0 0 0
"BRA" "ALB"  2 2012        451 9313.151 .3821138211382114                   1 0 0 0
"BRA" "ALB"  2 2013         54 9313.151 .3821138211382114   .3902439024390244 0 0 0
"BRA" "ALB"  2 2014       1387 9313.151 .2845528455284553   .7154471544715447 0 0 0
"BRA" "ARE"  3 2009   83546921 11809.98 .6991869918699187   .4065040650406504 0 0 0
"BRA" "ARE"  3 2010   23600914 11809.98 .4796747967479675   .3170731707317073 0 0 0
"BRA" "ARE"  3 2011   68742508 11809.98 .5934959349593496  .42276422764227645 0 0 0
"BRA" "ARE"  3 2012   45312701 11809.98 .3821138211382114  .13821138211382114 0 0 0
"BRA" "ARE"  3 2013   58465966 11809.98 .3821138211382114  .45528455284552843 0 0 0
"BRA" "ARE"  3 2014  176933670 11809.98 .2845528455284553   .5691056910569106 0 0 0
"BRA" "ARG"  4 2009 1199662929 2089.281 .6991869918699187   .5691056910569106 1 0 0
"BRA" "ARG"  4 2010 1575475673 2089.281 .4796747967479675   .8292682926829268 1 0 0
"BRA" "ARG"  4 2011 1850370799 2089.281 .5934959349593496   .6747967479674797 1 0 0
"BRA" "ARG"  4 2012 1641368735 2089.281 .3821138211382114  .35772357723577236 1 0 0
"BRA" "ARG"  4 2013 1328340316 2089.281 .3821138211382114   .3170731707317073 1 0 0
"BRA" "ARG"  4 2014 1133068766 2089.281 .2845528455284553  .17886178861788618 1 0 0
"BRA" "ARM"  5 2009         49  11214.9 .6991869918699187   .3252032520325203 0 0 0
"BRA" "ARM"  5 2010      35856  11214.9 .4796747967479675   .7398373983739838 0 0 0
"BRA" "ARM"  5 2011         24  11214.9 .5934959349593496  .12195121951219512 0 0 0
"BRA" "ARM"  5 2012       6590  11214.9 .3821138211382114   .0975609756097561 0 0 0
"BRA" "ARM"  5 2013         49  11214.9 .3821138211382114   .6016260162601627 0 0 0
"BRA" "ARM"  5 2014        244  11214.9 .2845528455284553   .3252032520325203 0 0 0
"BRA" "AUS"  6 2009   22302246 13983.36 .6991869918699187   .3008130081300813 0 0 0
"BRA" "AUS"  6 2010   20209779 13983.36 .4796747967479675   .4959349593495935 0 0 0
"BRA" "AUS"  6 2011   22328151 13983.36 .5934959349593496   .3170731707317073 0 0 0
"BRA" "AUS"  6 2012   23223800 13983.36 .3821138211382114   .6991869918699187 0 0 0
"BRA" "AUS"  6 2013   17347535 13983.36 .3821138211382114   .4878048780487805 0 0 0
"BRA" "AUS"  6 2014   30864179 13983.36 .2845528455284553   .5528455284552846 0 0 0
"BRA" "AUT"  7 2009    5313013 9395.406 .6991869918699187   .7235772357723578 0 0 0
"BRA" "AUT"  7 2010    6330983 9395.406 .4796747967479675  .35772357723577236 0 0 0
"BRA" "AUT"  7 2011    5698958 9395.406 .5934959349593496   .8455284552845529 0 0 0
"BRA" "AUT"  7 2012    1664144 9395.406 .3821138211382114   .7073170731707317 0 0 0
"BRA" "AUT"  7 2013    1395217 9395.406 .3821138211382114   .4634146341463415 0 0 0
"BRA" "AUT"  7 2014   16199355 9395.406 .2845528455284553   .8699186991869918 0 0 0
"BRA" "AZE"  8 2009      63514 11569.65 .6991869918699187   .7804878048780488 0 0 0
"BRA" "AZE"  8 2010          0 11569.65 .4796747967479675    .967479674796748 0 0 0
"BRA" "AZE"  8 2011        602 11569.65 .5934959349593496  .34959349593495936 0 0 0
"BRA" "AZE"  8 2012       2265 11569.65 .3821138211382114   .3008130081300813 0 0 0
"BRA" "AZE"  8 2013     219612 11569.65 .3821138211382114   .7804878048780488 0 0 0
"BRA" "AZE"  8 2014      51436 11569.65 .2845528455284553   .4146341463414634 0 0 0
"BRA" "BEL"  9 2009  117516351 8977.309 .6991869918699187   .3983739837398374 0 0 0
"BRA" "BEL"  9 2010  111740378 8977.309 .4796747967479675  .14634146341463414 0 0 0
"BRA" "BEL"  9 2011  188609683 8977.309 .5934959349593496   .7317073170731707 0 0 0
"BRA" "BEL"  9 2012  164059354 8977.309 .3821138211382114   .7479674796747967 0 0 0
"BRA" "BEL"  9 2013  114426142 8977.309 .3821138211382114  .15447154471544716 0 0 0
"BRA" "BEL"  9 2014  125515938 8977.309 .2845528455284553   .7560975609756098 0 0 0
"BRA" "BEN" 10 2009   16094862 5893.825 .6991869918699187   .0975609756097561 0 0 0
"BRA" "BEN" 10 2010    4151754 5893.825 .4796747967479675  .07317073170731707 0 0 0
"BRA" "BEN" 10 2011    9704038 5893.825 .5934959349593496   .0975609756097561 0 0 0
"BRA" "BEN" 10 2012    1780809 5893.825 .3821138211382114  .14634146341463414 0 0 0
"BRA" "BEN" 10 2013    4600869 5893.825 .3821138211382114   .2032520325203252 0 0 0
"BRA" "BEN" 10 2014     280249 5893.825 .2845528455284553  .13008130081300814 0 0 0
"BRA" "BGD" 11 2009    6610295 15292.22 .6991869918699187   .8617886178861789 0 0 0
"BRA" "BGD" 11 2010    3745866 15292.22 .4796747967479675   .5853658536585366 0 0 0
"BRA" "BGD" 11 2011    2797106 15292.22 .5934959349593496   .7398373983739838 0 0 0
"BRA" "BGD" 11 2012     423424 15292.22 .3821138211382114   .8780487804878049 0 0 0
"BRA" "BGD" 11 2013     887481 15292.22 .3821138211382114   .7967479674796748 0 0 0
"BRA" "BGD" 11 2014    2398781 15292.22 .2845528455284553   .7642276422764228 0 0 0
"BRA" "BGR" 12 2009     618688 9768.308 .6991869918699187  .25203252032520324 0 0 0
"BRA" "BGR" 12 2010     673776 9768.308 .4796747967479675  .25203252032520324 0 0 0
"BRA" "BGR" 12 2011     192542 9768.308 .5934959349593496  .06504065040650407 0 0 0
"BRA" "BGR" 12 2012     270882 9768.308 .3821138211382114   .5609756097560976 0 0 0
"BRA" "BGR" 12 2013     206898 9768.308 .3821138211382114   .6422764227642277 0 0 0
"BRA" "BGR" 12 2014     255623 9768.308 .2845528455284553  .08130081300813008 0 0 0
"BRA" "BHR" 13 2009     449527 11384.75 .6991869918699187  .06504065040650407 0 0 0
"BRA" "BHR" 13 2010     406267 11384.75 .4796747967479675  .21138211382113822 0 0 0
"BRA" "BHR" 13 2011     856167 11384.75 .5934959349593496  .17886178861788618 0 0 0
"BRA" "BHR" 13 2012   10449143 11384.75 .3821138211382114   .3983739837398374 0 0 0
"BRA" "BHR" 13 2013     209478 11384.75 .3821138211382114 .008130081300813009 0 0 0
"BRA" "BHR" 13 2014     194060 11384.75 .2845528455284553  .12195121951219512 0 0 0
"BRA" "BIH" 14 2009     323008 9351.396 .6991869918699187   .2032520325203252 0 0 0
"BRA" "BIH" 14 2010     559483 9351.396 .4796747967479675  .11382113821138211 0 0 0
"BRA" "BIH" 14 2011     416766 9351.396 .5934959349593496  .04065040650406504 0 0 0
"BRA" "BIH" 14 2012        929 9351.396 .3821138211382114   .5772357723577236 0 0 0
"BRA" "BIH" 14 2013      58609 9351.396 .3821138211382114   .5121951219512195 0 0 0
"BRA" "BIH" 14 2014      98829 9351.396 .2845528455284553 .008130081300813009 0 0 0
"BRA" "BLR" 15 2009     196491 10486.81 .6991869918699187  .18699186991869918 0 0 0
"BRA" "BLR" 15 2010     200535 10486.81 .4796747967479675   .5121951219512195 0 0 0
"BRA" "BLR" 15 2011     341227 10486.81 .5934959349593496  .10569105691056911 0 0 0
"BRA" "BLR" 15 2012     477479 10486.81 .3821138211382114  .04065040650406504 0 0 0
"BRA" "BLR" 15 2013     391021 10486.81 .3821138211382114   .6504065040650406 0 0 0
"BRA" "BLR" 15 2014     171054 10486.81 .2845528455284553  .14634146341463414 0 0 0
"BRA" "BOL" 16 2009  212279880 2266.878 .6991869918699187   .4959349593495935 1 0 0
"BRA" "BOL" 16 2010  275644036 2266.878 .4796747967479675   .2032520325203252 1 0 0
"BRA" "BOL" 16 2011  318939530 2266.878 .5934959349593496   .2926829268292683 1 0 0
"BRA" "BOL" 16 2012  319023235 2266.878 .3821138211382114  .06504065040650407 1 0 0
"BRA" "BOL" 16 2013  347332761 2266.878 .3821138211382114   .6747967479674797 1 0 0
"BRA" "BOL" 16 2014  359426904 2266.878 .2845528455284553  .21138211382113822 1 0 0
"BRA" "BRN" 17 2009      51951 17221.85 .6991869918699187   .6341463414634146 0 0 0
"BRA" "BRN" 17 2010      39346 17221.85 .4796747967479675   .3902439024390244 0 0 0
"BRA" "BRN" 17 2011      49940 17221.85 .5934959349593496  .16260162601626016 0 0 0
"BRA" "BRN" 17 2012       1876 17221.85 .3821138211382114   .5853658536585366 0 0 0
end
format %ty ANO
where:

ID_EXP: ISO code for exporter
ID_IMP: ISO code for importer
ID_NUM: numerical id for ID_IMP
EXP_NRB: the value of non-resource based exports
DIST: the distance between ID_EXP and ID_IMP
SCO_EXP, SCO_IMP: score of the strictness of environmental regulation for ID_EXP and ID_IMP respectively
FRO, LIN, COL: equal to 1 if ID_EXP has a border with ID_IMP, speak the same language and have colonial ties respectively, 0 otherwise

The commands I am running are the following:

Code:
tsset ID_NUM ANO, yearly
qui tab ID_NUM, gen(fe_ID_NUM)
ppml EXP_NRB DIST SCO_EXP SCO_IMP FRO LIN COL fe_ID_NUM*, cluster(DIST)
The result of my regression is (I've omitted the dummies for clarity):

Code:
Exports “NRB”
(1)
.
DIST -0.00***
(0.00)
SCO_EXP -0.59
(0.38)
SCO_IMP 0.52**
(0.24)
FRO -0.13**
(0.06)
LIN -0.39***
(0.03)
Constant 20.33***
(0.10)
Observations 714
R2 0.894 
 Standard errors in parentheses
* p < 0.10, ** p < 0.05, *** p < 0.01
I have a couple of questions:

1) Is the way I estimated my model correct? Because I have a 1xN model, I only estimated the importer fixed effects. Also, I clustered my errors based on the distance (should I use ln(distance)?). Is this correct?
2) Regarding the creation of ID_NUM, I simply assigned a sequence {1,2,3,...,n} of values to the column of importers, in such a way that AGO = 1, ALB = 2, etc. Is this correct?
3) Assuming the approach is correct, why would FRO and LIN be negative? In theory, countries that share a common border and/or language should trade more with each other, not less.

I appreciate immensely any help.

Kind regards,
Pedro

*ppml is a third-party command. You can install it using the following command:
Code:
 ssc install ppml