Hello! I am trying to estimate the impact of the Eurasian economic union (EAEU) on bilateral trade flows of its members. The estimation is carried out by implementing the gravity model of international trade. The results are obtained from the panel data covering the aggregate manufacturing sector of 60 countries (5 of them are members of the EAEU) over the period 2005-2017. I am using ppml in Stata 13.0.

Could anyone explain whether it is a problem if I include many dummies in the gravity equation? And how I can interpret interaction and dummy coefficients correctly?

Code:

Individuals effects for each member of the EAEU:

ppml import ln_GDP_exporter ln_GDP_importer ln_popul_exporter ln_popul_importer ln_distance contiguity common_lang2 same_country colonial_ties EAEU_both Armenia_EAEU Belarus_dummy Kazakhstan_dummy Kyrgyzstan_dummy Russia_dummy year pair_id if exporter != importer, cluster(pair_id)

In order to how the effect of the EAEU evolved over time:

ppml import ln_GDP_exporter ln_GDP_importer ln_popul_exporter ln_popul_importer ln_distance contiguity common_lang2 same_country EAEU_both_2005 EAEU_both_2006 EAEU_both_2007 EAEU_both_2008 EAEU_both_2009 EAEU_both_2010 EAEU_both_2011 EAEU_both_2012 EAEU_both_2013 EAEU_both_2014 EAEU_both_2015 EAEU_both_2016 EAEU_both_2017 year pair_id if exporter != importer, cluster(pair_id)

In order to distinguish the effects of the CIS (free trade area from 2012) and the EAEU (established in 2015):

ppml import ln_GDP_exporter ln_GDP_importer ln_popul_exporter ln_popul_importer ln_distance contiguity common_lang2 same_country colonial_ties CIS_both EAEU_both year pair_id if exporter != importer, cluster(pair_id)

Furthermore, I am a little bit confused by all the warnings on "large-values":

note: checking the existence of the estimates
WARNING: import has very large values, consider rescaling
WARNING: ln_GDP_exporter has very large values, consider rescaling or recentering
WARNING: ln_GDP_importer has very large values, consider rescaling or recentering
WARNING: ln_popul_exporter has very large values, consider rescaling or recentering
WARNING: ln_popul_importer has very large values, consider rescaling or recentering
WARNING: remoteness_importer has very large values, consider rescaling or recentering
WARNING: remoteness_exporter has very large values, consider rescaling or recentering

Number of regressors excluded to ensure that the estimates exist: 0
Number of observations excluded: 0

Is it a big issue?