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    PPML and Fixed Effects-FE producing different Directions of Signs?

    Hey everyone I am a undergraduate economic student doing my final capstone. I am trying to model Caribbean Tourism demand through the gravity model approach. I am running Panel FE and PPML-FE on STATA but one of my variables which is transporationcost has a coefficient sign of negative for Panel-FE and positive for PPML-FE. The expected sign should ne negative but I am wondering why its changing.

    I was also wondering for tourism is it better to have a country-fair fixed effect or fixed effect for both the origin and the destination?

    reg lnTourOD lnGDPpcO lnGDPpcD lnPopO lnPopD lnTransCost lnPrice lnSubPrice lnTCI Sites TS H1 H2 H3 H4 H5 i.CountryPairID i.Year
    note: 2019.Year omitted because of collinearity.

    Source | SS df MS Number of obs = 1,183
    -------------+---------------------------------- F(96, 1086) = 818.75
    Model | 4475.46392 96 46.6194159 Prob > F = 0.0000
    Residual | 61.8365422 1,086 .056939726 R-squared = 0.9864
    -------------+---------------------------------- Adj R-squared = 0.9852
    Total | 4537.30046 1,182 3.83866367 Root MSE = .23862

    -------------------------------------------------------------------------------
    lnTourOD | Coefficient Std. err. t P>|t| [95% conf. interval]
    --------------+----------------------------------------------------------------
    lnGDPpcO | 2.717557 .4111537 6.61 0.000 1.910811 3.524302
    lnGDPpcD | .5275286 .061168 8.62 0.000 .4075077 .6475496
    lnPopO | 9.225091 .9058236 10.18 0.000 7.447728 11.00245
    lnPopD | 1.156539 .1659294 6.97 0.000 .8309609 1.482118
    lnTransCost | -4.295607 .4269914 -10.06 0.000 -5.133429 -3.457786
    lnPrice | 2.109849 .4701474 4.49 0.000 1.187348 3.032349
    lnSubPrice | -1.62552 .4638966 -3.50 0.000 -2.535755 -.7152852
    lnTCI | .3534932 .211162 1.67 0.094 -.0608385 .7678248
    Sites | .0096387 .0089492 1.08 0.282 -.007921 .0271985
    TS | -.0185475 .0295509 -0.63 0.530 -.0765308 .0394359
    H1 | -.0769672 .03478 -2.21 0.027 -.1452109 -.0087236
    H2 | -.0374617 .0642931 -0.58 0.560 -.1636144 .088691
    H3 | -.032145 .0497229 -0.65 0.518 -.1297088 .0654187
    H4 | -.0855626 .0329932 -2.59 0.010 -.1503003 -.0208249
    H5 | -.061267 .0347029 -1.77 0.078 -.1293594 .0068254
    |
    CountryPairID |
    22 | -1.00991 .3279028 -3.08 0.002 -1.653305 -.3665154
    42 | .6530087 .342494 1.91 0.057 -.019016 1.325034
    62 | -2.049483 .5783824 -3.54 0.000 -3.184356 -.9146093
    82 | -1.137843 .5077468 -2.24 0.025 -2.134119 -.141567
    102 | -4.758011 .4750966 -10.01 0.000 -5.690222 -3.8258
    122 | -1.402693 .2891865 -4.85 0.000 -1.970121 -.8352656
    142 | -7.183284 1.125562 -6.38 0.000 -9.391807 -4.974762
    162 | -1.939191 .4024766 -4.82 0.000 -2.728911 -1.149471
    182 | -1.675379 .288463 -5.81 0.000 -2.241387 -1.109372
    202 | -2.832778 1.192914 -2.37 0.018 -5.173456 -.4921009
    222 | -1.069242 .3532932 -3.03 0.003 -1.762456 -.3760274
    242 | -3.134015 1.177257 -2.66 0.008 -5.44397 -.8240605
    262 | -.810962 1.049564 -0.77 0.440 -2.870364 1.24844
    282 | -6.115752 .590691 -10.35 0.000 -7.274777 -4.956727
    302 | -1.271515 .1962176 -6.48 0.000 -1.656523 -.8865061
    322 | -3.123786 .9373182 -3.33 0.001 -4.962946 -1.284627
    342 | -.8636195 .234263 -3.69 0.000 -1.323279 -.4039601
    362 | -.5318405 .4270072 -1.25 0.213 -1.369693 .306012
    382 | -1.494054 .3593459 -4.16 0.000 -2.199145 -.7889633
    422 | -2.206787 .7819839 -2.82 0.005 -3.741157 -.6724163
    462 | -.4639588 .371411 -1.25 0.212 -1.192723 .2648055
    482 | 17.32236 1.850085 9.36 0.000 13.69222 20.95251
    502 | 18.53967 1.869587 9.92 0.000 14.87126 22.20808
    522 | 16.36677 1.918048 8.53 0.000 12.60327 20.13027
    542 | 16.3778 2.042399 8.02 0.000 12.37031 20.3853
    562 | 18.28754 1.915968 9.54 0.000 14.52813 22.04696
    582 | 15.60576 1.806977 8.64 0.000 12.0602 19.15132
    642 | 16.57554 1.916811 8.65 0.000 12.81447 20.33662
    662 | 14.76359 2.246944 6.57 0.000 10.35475 19.17243
    682 | 14.68634 1.924644 7.63 0.000 10.9099 18.46279
    702 | 16.5427 1.867609 8.86 0.000 12.87817 20.20723
    722 | 15.57632 2.151586 7.24 0.000 11.35458 19.79805
    742 | 17.8028 1.892876 9.41 0.000 14.08869 21.51691
    782 | 17.96119 2.107447 8.52 0.000 13.82606 22.09632
    802 | 18.48325 1.864747 9.91 0.000 14.82434 22.14217
    822 | 10.71486 2.051017 5.22 0.000 6.690456 14.73926
    842 | 17.02701 1.859256 9.16 0.000 13.37887 20.67515
    862 | 18.19653 1.896292 9.60 0.000 14.47572 21.91734
    882 | 17.1998 1.886856 9.12 0.000 13.49751 20.9021
    902 | 15.36638 2.027847 7.58 0.000 11.38744 19.34532
    942 | 13.25375 1.876095 7.06 0.000 9.572564 16.93493
    982 | 18.7005 2.067611 9.04 0.000 14.64354 22.75747
    1002 | 18.92481 2.106221 8.99 0.000 14.79209 23.05754
    1022 | 19.14281 2.125253 9.01 0.000 14.97274 23.31288
    1042 | 16.97194 2.08446 8.14 0.000 12.88191 21.06197
    1062 | 19.49252 2.182661 8.93 0.000 15.20981 23.77523
    1082 | 15.64647 1.927958 8.12 0.000 11.86352 19.42941
    1142 | 17.18543 2.03635 8.44 0.000 13.1898 21.18105
    1162 | 16.05208 2.311938 6.94 0.000 11.51571 20.58845
    1182 | 17.68029 2.136105 8.28 0.000 13.48893 21.87165
    1202 | 17.85704 2.114642 8.44 0.000 13.70779 22.00629
    1222 | 17.87082 2.331433 7.67 0.000 13.2962 22.44545
    1242 | 18.83522 2.148849 8.77 0.000 14.61885 23.05158
    1262 | 16.14152 2.352586 6.86 0.000 11.52539 20.75765
    1282 | 18.87313 2.2579 8.36 0.000 14.44279 23.30348
    1302 | 15.31368 2.190501 6.99 0.000 11.01559 19.61177
    1322 | 18.72343 2.089969 8.96 0.000 14.62259 22.82426
    1342 | 13.36976 2.252268 5.94 0.000 8.950474 17.78906
    1362 | 18.46869 2.088201 8.84 0.000 14.37133 22.56606
    1382 | 19.33159 2.150773 8.99 0.000 15.11145 23.55173
    1402 | 18.68609 2.14258 8.72 0.000 14.48203 22.89016
    1462 | 17.82223 2.269354 7.85 0.000 13.36941 22.27504
    1502 | 18.43933 2.252219 8.19 0.000 14.02013 22.85852
    |
    Year |
    2001 | -.748402 .101271 -7.39 0.000 -.9471111 -.549693
    2002 | -.8483074 .1023078 -8.29 0.000 -1.049051 -.6475641
    2003 | -.7710353 .0917029 -8.41 0.000 -.9509701 -.5911004
    2004 | -.0611945 .0478574 -1.28 0.201 -.1550979 .0327089
    2005 | 1.154256 .1348003 8.56 0.000 .8897579 1.418755
    2006 | 1.741284 .1870712 9.31 0.000 1.374222 2.108346
    2007 | 1.759157 .1858813 9.46 0.000 1.39443 2.123884
    2008 | 2.743824 .2842037 9.65 0.000 2.186174 3.301475
    2009 | .902053 .1125425 8.02 0.000 .6812277 1.122878
    2010 | 1.914014 .2074052 9.23 0.000 1.507053 2.320974
    2011 | 2.780135 .2945969 9.44 0.000 2.202092 3.358179
    2012 | 2.811493 .297932 9.44 0.000 2.226905 3.39608
    2013 | 2.680963 .2862193 9.37 0.000 2.119358 3.242569
    2014 | 2.207419 .2339382 9.44 0.000 1.748397 2.666441
    2015 | -.2447681 .0480758 -5.09 0.000 -.3391001 -.1504361
    2016 | -.9520614 .1085735 -8.77 0.000 -1.165099 -.7390238
    2017 | -.2533055 .0517228 -4.90 0.000 -.3547934 -.1518175
    2018 | .4760542 .0707698 6.73 0.000 .3371932 .6149153
    2019 | 0 (omitted)
    |
    _cons | -66.92603 8.688792 -7.70 0.000 -83.97475 -49.87731
    -------------------------------------------------------------------------------

    . xtreg lnTourOD lnGDPpcO lnGDPpcD lnPopO lnPopD lnTransCost lnPrice lnSubPrice lnTCI Sites TS H1 H2 H3 H4 H5 i.Year, fe
    note: 2019.Year omitted because of collinearity.

    Fixed-effects (within) regression Number of obs = 1,183
    Group variable: CountryPai~D Number of groups = 64

    R-squared: Obs per group:
    Within = 0.4551 min = 9
    Between = 0.3304 avg = 18.5
    Overall = 0.3410 max = 20

    F(33, 1086) = 27.48
    corr(u_i, Xb) = -0.9853 Prob > F = 0.0000

    ------------------------------------------------------------------------------
    lnTourOD | Coefficient Std. err. t P>|t| [95% conf. interval]
    -------------+----------------------------------------------------------------
    lnGDPpcO | 2.717557 .4111537 6.61 0.000 1.910811 3.524302
    lnGDPpcD | .5275286 .061168 8.62 0.000 .4075077 .6475496
    lnPopO | 9.225091 .9058236 10.18 0.000 7.447728 11.00245
    lnPopD | 1.156539 .1659294 6.97 0.000 .8309609 1.482118
    lnTransCost | -4.295607 .4269914 -10.06 0.000 -5.133429 -3.457786
    lnPrice | 2.109849 .4701474 4.49 0.000 1.187348 3.032349
    lnSubPrice | -1.62552 .4638966 -3.50 0.000 -2.535755 -.7152852
    lnTCI | .3534932 .211162 1.67 0.094 -.0608385 .7678248
    Sites | .0096387 .0089492 1.08 0.282 -.007921 .0271985
    TS | -.0185475 .0295509 -0.63 0.530 -.0765308 .0394359
    H1 | -.0769672 .03478 -2.21 0.027 -.1452109 -.0087236
    H2 | -.0374617 .0642931 -0.58 0.560 -.1636144 .088691
    H3 | -.032145 .0497229 -0.65 0.518 -.1297088 .0654187
    H4 | -.0855626 .0329932 -2.59 0.010 -.1503003 -.0208249
    H5 | -.061267 .0347029 -1.77 0.078 -.1293594 .0068254
    |
    Year |
    2001 | -.748402 .101271 -7.39 0.000 -.9471111 -.549693
    2002 | -.8483074 .1023078 -8.29 0.000 -1.049051 -.6475641
    2003 | -.7710353 .0917029 -8.41 0.000 -.9509701 -.5911004
    2004 | -.0611945 .0478574 -1.28 0.201 -.1550979 .0327089
    2005 | 1.154256 .1348003 8.56 0.000 .8897579 1.418755
    2006 | 1.741284 .1870712 9.31 0.000 1.374222 2.108346
    2007 | 1.759157 .1858813 9.46 0.000 1.39443 2.123884
    2008 | 2.743824 .2842037 9.65 0.000 2.186174 3.301475
    2009 | .902053 .1125425 8.02 0.000 .6812277 1.122878
    2010 | 1.914014 .2074052 9.23 0.000 1.507053 2.320974
    2011 | 2.780135 .2945969 9.44 0.000 2.202092 3.358179
    2012 | 2.811493 .297932 9.44 0.000 2.226905 3.39608
    2013 | 2.680963 .2862193 9.37 0.000 2.119358 3.242569
    2014 | 2.207419 .2339382 9.44 0.000 1.748397 2.666441
    2015 | -.2447681 .0480758 -5.09 0.000 -.3391001 -.1504361
    2016 | -.9520614 .1085735 -8.77 0.000 -1.165099 -.7390238
    2017 | -.2533055 .0517228 -4.90 0.000 -.3547934 -.1518175
    2018 | .4760542 .0707698 6.73 0.000 .3371932 .6149153
    2019 | 0 (omitted)
    |
    _cons | -56.34374 7.588916 -7.42 0.000 -71.23433 -41.45314
    -------------+----------------------------------------------------------------
    sigma_u | 9.3185714
    sigma_e | .23862046
    rho | .99934471 (fraction of variance due to u_i)
    ------------------------------------------------------------------------------
    F test that all u_i=0: F(63, 1086) = 399.27 Prob > F = 0.0000

    . ppml lnTourOD lnGDPpcO lnGDPpcD lnPopO lnPopD lnTransCost lnPrice lnSubPrice lnTCI Sites TS H1 H2 H3 H4 H5 CountryPairID* i.Year*
    factor-variable and time-series operators not allowed
    r(101);

    . ppml lnTourOD lnGDPpcO lnGDPpcD lnPopO lnPopD lnTransCost lnPrice lnSubPrice lnTCI Sites TS H1 H2 H3 H4 H5 Year* CountryPairID*

    note: checking the existence of the estimates
    WARNING: lnTransCost has very large values, consider rescaling or recentering
    WARNING: Sites has very large values, consider rescaling or recentering
    WARNING: Year has very large values, consider rescaling or recentering
    WARNING: CountryPairID has very large values, consider rescaling or recentering

    Number of regressors excluded to ensure that the estimates exist: 13
    Excluded regressors: Year1 Year20 CountryPairID6 CountryPairID21 CountryPairID23 CountryPairID31 CountryPairID33 CountryPairID38 CountryPairID46 CountryPairID54 CountryP
    > airID69 CountryPairID71 CountryPairID72
    Number of observations excluded: 0

    note: starting ppml estimation
    note: lnTourOD has noninteger values

    Iteration 1: Deviance = 6.707953
    Iteration 2: Deviance = 6.042355
    Iteration 3: Deviance = 6.042223
    Iteration 4: Deviance = 6.042223

    Number of parameters: 97
    Number of observations: 1183
    Pseudo log-likelihood: -2482.2638
    R-squared: .98651503
    Option strict is: off
    ---------------------------------------------------------------------------------
    | Robust
    lnTourOD | Coefficient std. err. z P>|z| [95% conf. interval]
    ----------------+----------------------------------------------------------------
    lnGDPpcO | .274305 .0350326 7.83 0.000 .2056425 .3429676
    lnGDPpcD | .0439261 .0065638 6.69 0.000 .0310613 .0567909
    lnPopO | .9683123 .0956746 10.12 0.000 .7807935 1.155831
    lnPopD | .1069192 .0145691 7.34 0.000 .0783644 .1354741
    lnTransCost | .471768 .0842369 5.60 0.000 .3066667 .6368693
    lnPrice | .2141357 .0394344 5.43 0.000 .1368458 .2914256
    lnSubPrice | -.1632469 .0377525 -4.32 0.000 -.2372404 -.0892534
    lnTCI | .0359181 .0195707 1.84 0.066 -.0024397 .0742759
    Sites | -.0000647 .0006666 -0.10 0.923 -.0013713 .0012419
    TS | -.0004433 .0024171 -0.18 0.854 -.0051808 .0042942
    H1 | -.0067327 .0032963 -2.04 0.041 -.0131934 -.000272
    H2 | -.0029645 .0038942 -0.76 0.447 -.010597 .004668
    H3 | -.0025061 .0040652 -0.62 0.538 -.0104738 .0054616
    H4 | -.0067646 .0026531 -2.55 0.011 -.0119646 -.0015647
    H5 | -.0067181 .0043178 -1.56 0.120 -.0151808 .0017447
    Year | -.0343658 .004041 -8.50 0.000 -.042286 -.0264455
    Year2 | .064027 .013443 4.76 0.000 .0376791 .0903749
    Year3 | .0865668 .0165293 5.24 0.000 .05417 .1189636
    Year4 | .0676842 .013837 4.89 0.000 .0405642 .0948041
    Year5 | -.0168019 .0050068 -3.36 0.001 -.0266151 -.0069888
    Year6 | -.178444 .0280236 -6.37 0.000 -.2333692 -.1235188
    Year7 | -.2544472 .0408009 -6.24 0.000 -.3344156 -.1744789
    Year8 | -.2702598 .0429121 -6.30 0.000 -.3543659 -.1861538
    Year9 | -.381702 .0624648 -6.11 0.000 -.5041307 -.2592734
    Year10 | -.1488381 .023277 -6.39 0.000 -.1944602 -.1032159
    Year11 | -.2545224 .0421814 -6.03 0.000 -.3371965 -.1718483
    Year12 | -.3491598 .0590609 -5.91 0.000 -.4649171 -.2334026
    Year13 | -.3485069 .0593199 -5.88 0.000 -.4647718 -.232242
    Year14 | -.3270161 .0559768 -5.84 0.000 -.4367287 -.2173035
    Year15 | -.2676631 .0462077 -5.79 0.000 -.3582285 -.1770977
    Year16 | .0192103 .0049836 3.85 0.000 .0094427 .0289779
    Year17 | .1232687 .020209 6.10 0.000 .0836597 .1628777
    Year18 | .0427657 .0075239 5.68 0.000 .0280192 .0575122
    Year19 | -.0629389 .0119834 -5.25 0.000 -.0864259 -.039452
    CountryPairID | .000784 .0001138 6.89 0.000 .0005611 .001007
    CountryPairID1 | -.1513503 .0885438 -1.71 0.087 -.3248931 .0221924
    CountryPairID2 | -.3121853 .0706953 -4.42 0.000 -.4507456 -.173625
    CountryPairID3 | -.2759209 .0751584 -3.67 0.000 -.4232286 -.1286131
    CountryPairID4 | -.0523507 .0188725 -2.77 0.006 -.0893401 -.0153612
    CountryPairID5 | -.5125535 .0739699 -6.93 0.000 -.6575319 -.3675751
    CountryPairID7 | -.3088989 .0594049 -5.20 0.000 -.4253303 -.1924675
    CountryPairID8 | -.7082741 .0654487 -10.82 0.000 -.8365512 -.5799969
    CountryPairID9 | -.6077438 .0762982 -7.97 0.000 -.7572855 -.4582022
    CountryPairID10 | -.5659708 .0832601 -6.80 0.000 -.7291576 -.402784
    CountryPairID11 | -.5217409 .081864 -6.37 0.000 -.6821913 -.3612905
    CountryPairID12 | -.6228515 .0890467 -6.99 0.000 -.7973798 -.4483231
    CountryPairID13 | -.5496784 .0891443 -6.17 0.000 -.724398 -.3749588
    CountryPairID14 | -.3937446 .0953869 -4.13 0.000 -.5806995 -.2067898
    CountryPairID15 | -1.102848 .0763011 -14.45 0.000 -1.252395 -.9533007
    CountryPairID16 | -.6187287 .1075221 -5.75 0.000 -.8294681 -.4079892
    CountryPairID17 | -.7083941 .0699052 -10.13 0.000 -.8454058 -.5713824
    CountryPairID18 | -.530868 .0832753 -6.37 0.000 -.6940846 -.3676514
    CountryPairID19 | -.6387337 .0887502 -7.20 0.000 -.8126809 -.4647865
    CountryPairID20 | -.7644834 .0947208 -8.07 0.000 -.9501328 -.578834
    CountryPairID22 | -.9183696 .0930518 -9.87 0.000 -1.100748 -.7359915
    CountryPairID24 | -.6269331 .0853711 -7.34 0.000 -.7942574 -.4596089
    CountryPairID25 | .4581512 .1095174 4.18 0.000 .2435011 .6728014
    CountryPairID26 | .5913801 .08235 7.18 0.000 .4299771 .7527831
    CountryPairID27 | .245649 .0837708 2.93 0.003 .0814613 .4098368
    CountryPairID28 | .3091205 .0551386 5.61 0.000 .2010509 .4171901
    CountryPairID29 | .4905723 .064423 7.61 0.000 .3643056 .616839
    CountryPairID30 | .4058585 .0689593 5.89 0.000 .2707006 .5410163
    CountryPairID32 | .1518851 .0810026 1.88 0.061 -.0068771 .3106473
    CountryPairID34 | -.0663028 .0659998 -1.00 0.315 -.19566 .0630544
    CountryPairID35 | .2069657 .0731334 2.83 0.005 .0636269 .3503045
    CountryPairID36 | .1004634 .0680788 1.48 0.140 -.0329685 .2338953
    CountryPairID37 | .2778923 .0683928 4.06 0.000 .1438449 .4119396
    CountryPairID39 | .211647 .0914899 2.31 0.021 .0323302 .3909638
    CountryPairID40 | .2925108 .1054384 2.77 0.006 .0858554 .4991663
    CountryPairID41 | -.4349555 .0145565 -29.88 0.000 -.4634857 -.4064253
    CountryPairID42 | .1672856 .0696553 2.40 0.016 .0307638 .3038074
    CountryPairID43 | .2497919 .0559686 4.46 0.000 .1400955 .3594883
    CountryPairID44 | .122763 .0622394 1.97 0.049 .0007761 .2447499
    CountryPairID45 | -.0737719 .0454815 -1.62 0.105 -.162914 .0153701
    CountryPairID47 | -.3313311 .0494313 -6.70 0.000 -.4282147 -.2344476
    CountryPairID48 | .8667906 .0861818 10.06 0.000 .6978773 1.035704
    CountryPairID49 | .8725128 .0749043 11.65 0.000 .725703 1.019323
    CountryPairID50 | .8343374 .0680188 12.27 0.000 .7010229 .9676519
    CountryPairID51 | 1.088733 .1087174 10.01 0.000 .8756513 1.301816
    CountryPairID52 | .763998 .0615585 12.41 0.000 .6433455 .8846505
    CountryPairID53 | 1.062218 .1052497 10.09 0.000 .8559325 1.268504
    CountryPairID55 | .7948862 .0712869 11.15 0.000 .6551664 .9346059
    CountryPairID56 | .7951749 .1253542 6.34 0.000 .5494852 1.040865
    CountryPairID57 | .5423654 .052668 10.30 0.000 .439138 .6455929
    CountryPairID58 | .5215951 .0550806 9.47 0.000 .4136391 .6295511
    CountryPairID59 | .7245263 .1130033 6.41 0.000 .503044 .9460087
    CountryPairID60 | .5398254 .0477718 11.30 0.000 .4461944 .6334564
    CountryPairID61 | .5616629 .1186428 4.73 0.000 .3291273 .7941985
    CountryPairID62 | .8059123 .1152184 6.99 0.000 .5800885 1.031736
    CountryPairID63 | .2018674 .0514338 3.92 0.000 .101059 .3026758
    CountryPairID64 | .4639136 .0621832 7.46 0.000 .3420368 .5857905
    CountryPairID65 | .1760709 .086406 2.04 0.042 .0067183 .3454235
    CountryPairID66 | .5504487 .0479856 11.47 0.000 .4563986 .6444987
    CountryPairID67 | .5289964 .0444032 11.91 0.000 .4419677 .616025
    CountryPairID68 | .418188 .0413731 10.11 0.000 .3370981 .4992779
    CountryPairID70 | .265698 .0605822 4.39 0.000 .146959 .3844369
    _cons | 52.00591 6.36391 8.17 0.000 39.53287 64.47894
    ---------------------------------------------------------------------------------

    . ppml lnTourOD lnGDPpcO lnGDPpcD lnPopO lnPopD lnTransCost lnPrice lnSubPrice lnTCI Sites TS H1 H2 H3 H4 H5 CountryPairID* Year*

    note: checking the existence of the estimates
    WARNING: lnTransCost has very large values, consider rescaling or recentering
    WARNING: Sites has very large values, consider rescaling or recentering
    WARNING: CountryPairID has very large values, consider rescaling or recentering
    WARNING: Year has very large values, consider rescaling or recentering

    Number of regressors excluded to ensure that the estimates exist: 13
    Excluded regressors: CountryPairID6 CountryPairID21 CountryPairID23 CountryPairID31 CountryPairID33 CountryPairID38 CountryPairID46 CountryPairID54 CountryPairID69 Count
    > ryPairID71 CountryPairID72 Year1 Year20
    Number of observations excluded: 0

    note: starting ppml estimation
    note: lnTourOD has noninteger values

    Iteration 1: Deviance = 6.707953
    Iteration 2: Deviance = 6.042355
    Iteration 3: Deviance = 6.042223
    Iteration 4: Deviance = 6.042223

    Number of parameters: 97
    Number of observations: 1183
    Pseudo log-likelihood: -2482.2638
    R-squared: .98651503
    Option strict is: off
    ---------------------------------------------------------------------------------
    | Robust
    lnTourOD | Coefficient std. err. z P>|z| [95% conf. interval]
    ----------------+----------------------------------------------------------------
    lnGDPpcO | .274305 .0350326 7.83 0.000 .2056425 .3429676
    lnGDPpcD | .0439261 .0065638 6.69 0.000 .0310613 .0567909
    lnPopO | .9683123 .0956746 10.12 0.000 .7807935 1.155831
    lnPopD | .1069192 .0145691 7.34 0.000 .0783643 .1354741
    lnTransCost | .471768 .0842369 5.60 0.000 .3066666 .6368693
    lnPrice | .2141357 .0394344 5.43 0.000 .1368458 .2914257
    lnSubPrice | -.1632469 .0377525 -4.32 0.000 -.2372404 -.0892534
    lnTCI | .0359181 .0195707 1.84 0.066 -.0024397 .0742759
    Sites | -.0000647 .0006666 -0.10 0.923 -.0013713 .0012419
    TS | -.0004433 .0024171 -0.18 0.854 -.0051808 .0042942
    H1 | -.0067327 .0032963 -2.04 0.041 -.0131934 -.000272
    H2 | -.0029645 .0038942 -0.76 0.447 -.010597 .004668
    H3 | -.0025061 .0040652 -0.62 0.538 -.0104738 .0054616
    H4 | -.0067646 .0026531 -2.55 0.011 -.0119646 -.0015647
    H5 | -.0067181 .0043178 -1.56 0.120 -.0151808 .0017447
    CountryPairID | .000784 .0001138 6.89 0.000 .0005611 .001007
    CountryPairID1 | -.1513503 .0885438 -1.71 0.087 -.3248931 .0221924
    CountryPairID2 | -.3121853 .0706953 -4.42 0.000 -.4507456 -.173625
    CountryPairID3 | -.2759209 .0751584 -3.67 0.000 -.4232286 -.1286131
    CountryPairID4 | -.0523507 .0188725 -2.77 0.006 -.0893401 -.0153612
    CountryPairID5 | -.5125535 .07397 -6.93 0.000 -.657532 -.367575
    CountryPairID7 | -.3088989 .0594049 -5.20 0.000 -.4253304 -.1924675
    CountryPairID8 | -.7082741 .0654487 -10.82 0.000 -.8365512 -.5799969
    CountryPairID9 | -.6077438 .0762982 -7.97 0.000 -.7572855 -.4582021
    CountryPairID10 | -.5659708 .0832601 -6.80 0.000 -.7291576 -.402784
    CountryPairID11 | -.5217409 .081864 -6.37 0.000 -.6821913 -.3612905
    CountryPairID12 | -.6228515 .0890467 -6.99 0.000 -.7973798 -.4483231
    CountryPairID13 | -.5496784 .0891443 -6.17 0.000 -.724398 -.3749588
    CountryPairID14 | -.3937446 .0953869 -4.13 0.000 -.5806995 -.2067898
    CountryPairID15 | -1.102848 .0763011 -14.45 0.000 -1.252395 -.9533007
    CountryPairID16 | -.6187287 .1075221 -5.75 0.000 -.8294682 -.4079892
    CountryPairID17 | -.7083941 .0699052 -10.13 0.000 -.8454058 -.5713824
    CountryPairID18 | -.530868 .0832753 -6.37 0.000 -.6940847 -.3676514
    CountryPairID19 | -.6387337 .0887502 -7.20 0.000 -.8126809 -.4647864
    CountryPairID20 | -.7644834 .0947208 -8.07 0.000 -.9501328 -.5788339
    CountryPairID22 | -.9183696 .0930518 -9.87 0.000 -1.100748 -.7359915
    CountryPairID24 | -.6269331 .0853711 -7.34 0.000 -.7942574 -.4596088
    CountryPairID25 | .4581512 .1095174 4.18 0.000 .2435011 .6728014
    CountryPairID26 | .5913801 .08235 7.18 0.000 .4299771 .7527831
    CountryPairID27 | .245649 .0837708 2.93 0.003 .0814613 .4098368
    CountryPairID28 | .3091205 .0551386 5.61 0.000 .2010509 .4171901
    CountryPairID29 | .4905723 .064423 7.61 0.000 .3643056 .616839
    CountryPairID30 | .4058585 .0689593 5.89 0.000 .2707006 .5410163
    CountryPairID32 | .1518851 .0810026 1.88 0.061 -.0068771 .3106473
    CountryPairID34 | -.0663028 .0659998 -1.00 0.315 -.19566 .0630544
    CountryPairID35 | .2069657 .0731334 2.83 0.005 .0636269 .3503045
    CountryPairID36 | .1004634 .0680788 1.48 0.140 -.0329685 .2338953
    CountryPairID37 | .2778923 .0683928 4.06 0.000 .1438449 .4119396
    CountryPairID39 | .211647 .0914899 2.31 0.021 .0323302 .3909638
    CountryPairID40 | .2925108 .1054384 2.77 0.006 .0858554 .4991663
    CountryPairID41 | -.4349555 .0145565 -29.88 0.000 -.4634857 -.4064253
    CountryPairID42 | .1672856 .0696553 2.40 0.016 .0307638 .3038074
    CountryPairID43 | .2497919 .0559686 4.46 0.000 .1400955 .3594884
    CountryPairID44 | .122763 .0622394 1.97 0.049 .0007761 .2447499
    CountryPairID45 | -.0737719 .0454815 -1.62 0.105 -.162914 .0153701
    CountryPairID47 | -.3313311 .0494313 -6.70 0.000 -.4282147 -.2344476
    CountryPairID48 | .8667906 .0861818 10.06 0.000 .6978773 1.035704
    CountryPairID49 | .8725128 .0749043 11.65 0.000 .725703 1.019323
    CountryPairID50 | .8343374 .0680189 12.27 0.000 .7010229 .9676519
    CountryPairID51 | 1.088733 .1087174 10.01 0.000 .8756512 1.301816
    CountryPairID52 | .763998 .0615585 12.41 0.000 .6433455 .8846505
    CountryPairID53 | 1.062218 .1052497 10.09 0.000 .8559325 1.268504
    CountryPairID55 | .7948862 .0712869 11.15 0.000 .6551664 .9346059
    CountryPairID56 | .7951749 .1253542 6.34 0.000 .5494852 1.040865
    CountryPairID57 | .5423654 .052668 10.30 0.000 .439138 .6455929
    CountryPairID58 | .5215951 .0550806 9.47 0.000 .4136391 .6295511
    CountryPairID59 | .7245263 .1130033 6.41 0.000 .503044 .9460087
    CountryPairID60 | .5398254 .0477718 11.30 0.000 .4461944 .6334564
    CountryPairID61 | .5616629 .1186428 4.73 0.000 .3291273 .7941985
    CountryPairID62 | .8059123 .1152184 6.99 0.000 .5800885 1.031736
    CountryPairID63 | .2018674 .0514338 3.92 0.000 .1010589 .3026759
    CountryPairID64 | .4639136 .0621832 7.46 0.000 .3420368 .5857905
    CountryPairID65 | .1760709 .086406 2.04 0.042 .0067183 .3454235
    CountryPairID66 | .5504487 .0479856 11.47 0.000 .4563986 .6444987
    CountryPairID67 | .5289964 .0444032 11.91 0.000 .4419677 .6160251
    CountryPairID68 | .418188 .0413732 10.11 0.000 .3370981 .4992779
    CountryPairID70 | .265698 .0605822 4.39 0.000 .146959 .3844369
    Year | -.0343658 .004041 -8.50 0.000 -.042286 -.0264455
    Year2 | .064027 .013443 4.76 0.000 .0376791 .0903749
    Year3 | .0865668 .0165293 5.24 0.000 .05417 .1189636
    Year4 | .0676842 .013837 4.89 0.000 .0405642 .0948041
    Year5 | -.0168019 .0050068 -3.36 0.001 -.0266151 -.0069888
    Year6 | -.178444 .0280236 -6.37 0.000 -.2333692 -.1235188
    Year7 | -.2544472 .0408009 -6.24 0.000 -.3344156 -.1744789
    Year8 | -.2702598 .0429121 -6.30 0.000 -.354366 -.1861537
    Year9 | -.381702 .0624648 -6.11 0.000 -.5041307 -.2592733
    Year10 | -.1488381 .023277 -6.39 0.000 -.1944602 -.1032159
    Year11 | -.2545224 .0421814 -6.03 0.000 -.3371965 -.1718483
    Year12 | -.3491598 .0590609 -5.91 0.000 -.4649171 -.2334025
    Year13 | -.3485069 .0593199 -5.88 0.000 -.4647718 -.232242
    Year14 | -.3270161 .0559768 -5.84 0.000 -.4367287 -.2173035
    Year15 | -.2676631 .0462077 -5.79 0.000 -.3582285 -.1770977
    Year16 | .0192103 .0049836 3.85 0.000 .0094427 .0289779
    Year17 | .1232687 .020209 6.10 0.000 .0836597 .1628777
    Year18 | .0427657 .0075239 5.68 0.000 .0280192 .0575122
    Year19 | -.0629389 .0119834 -5.25 0.000 -.0864259 -.039452
    _cons | 52.00591 6.363911 8.17 0.000 39.53287 64.47894
    ---------------------------------------------------------------------------------
    Tags: None
  • #2
    Dear Benjamin Carlson,

    When you use PPML, your dependent variable should not be in logs. Also, lease use the user-written commands reghdfe and ppmlhdfe so that you can "absorb" the fixed effects (check the help file for examples). As for fixed effects, I would start with origin and destination FE.

    Best wishes,

    Joao

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