Extensive vs. intensive forms of migration and bilateral trade.

Gravity-model estimation. Full-sample (pooled) ordinary least-square (OLS) fit. Years y = 1960, …, 2000. Dependent variable: logs of total bilateral trade τijy=tijy+tjiy. Country-year dummy variables for importer/exporter effects and constant included. Explanatory variables: log(IN_CENTRijy)B = country i and jin-degree (binary) centralization; log(IN_CENTRijy)W = country i and jin-strength (weighted) centralization. WD (p-val): Wooldridge-Drukker F-test for serial correlation in linear panel-data models (p-value) [41, 42]. Significance levels: *** = 1%, ** = 5%, * = 10%.