Ogranicenja gravitacionog modela u ekonometrijskoj analizi spoljnotrgovinske razmene

This work deals with econometric modeling of bilateral trade flows based on gravity model. Standard approach in most of previous empirical researches consisted of estimating bilateral trade potentials using gravity model and analysis of differences between the observed and predicted (potential) trade flows. Large differences were interpreted as the unexhausted foreign trade potentials. This work considers some limitations and problems of such approach mostly based on cross-section data. We consider alternative gravity model specifications with panel data and estimating procedures, as appropriate base for more precise estimates and conclusions. Furthermore, both theoretical and empirical analysis of econometric problems in panel data gravity model are carried out. Some of those problems have considered partially in previous empirical researches (for example autocorrelation in panels), but some of them have not considered at all, such as double endogenous regressors. Empirical results show that mentioned problems cause biased regression parameters estimates and consequently systematic variations of gravity model residuals (large systematic differences between observed and predicted). This makes conclusions on trade potentials between countries imprecise and unreliable. Predmet razmatranja u ovom radu je ekonometrijsko modeliranje bilateralne razmene na bazi gravitacionog modela. U dosadasnjim istrazivanjima gravitacioni model je standardno koriscen u svrhe ocenjivanja potencijala bilateralne razmene medju zemljama. Procene mogucnosti za njen porast vrsene su na osnovu odstupanja ostvarenog od potencijalnog, modelom ocenjenog nivoa razmene. U ovom radu se ukazuje na odredjena ogranicenja takve standardne analize, najcesce zasnovane na uporednim podacima (podacima preseka). Stoga se razmatraju alternativne specifikacije gravitacionog modela na podacima panela i moguce efikasnije procedure ocenjivanja, kao osnove za pouzdanije ekonomske zakljucke. Takodje, sprovedena je teorijska i empirijska analiza ekonometrijskih problema u ocenjivanju gravitacionog modela panela, koji su u dosadasnjoj literaturi ili izolovano posmatrani (na primer autokorelacija u panelu), ili uopste nisu razmatrani (na primer, dvostruka endogenost regresora). Na osnovu empirijske analize pokazano je da razmatrani problemi i ogranicenja uzrokuju pristrasne ocene regresionih parametara i sistematske varijacije reziduala gravitacionog modela. Na bazi takvih rezultata, predvidjanje i zakljuciv