Trade Costs, Regional Integration, and Bilateral Exports in Asian Landlocked Developing Countries: A PPML Gravity Analysis

Landlocked developing countries (LLDCs) face persistent trade-cost disadvantages arising from distance, transit dependence, border frictions, and uneven logistics performance. This study reconstructs bilateral merchandise exports for 11 Asian LLDCs to a common set of 50 large importing markets over 2010–2024 and evaluates export correlates using Poisson pseudo-maximum-likelihood (PPML) gravity models. The trade-eligible sample comprises 6800 exporter–importer–year observations, including 993 source-validated constructed zeros; source-missing observations are not treated as zeros. Models progress from a conventional gravity benchmark with year fixed effects to pair-fixed-effects specifications and structural gravity with exporter–year, importer–year, and pair fixed effects; standard errors are clustered by dyad. The conventional benchmark finds positive exporter and importer gross domestic product (GDP) coefficients and a negative distance coefficient. Logistics Performance Index coefficients are not robustly significant after introducing pair fixed effects. Bilateral effectively applied tariff coefficients are generally negative but not significant at the 5% level. Bilateral Eurasian Economic Union (EAEU) membership has positive coefficients across reported specifications, although statistical significance is not uniform, including in the tariff-augmented pair-fixed-effects model. The association remains positive and significant in structural-gravity models estimated over 2013–2024 using a destination ranking fixed from 2010 to 2012, with and without tariffs; leave-one-switching-dyad-out checks preserve the positive structural estimate. These are conditional associations, not causal treatment effects. Generalizability is constrained by the selected destination universe and only three EAEU-switching dyads.