4.2. Data
For bilateral trade flows, we use import and export values in US dollars at SITC
2-digit level taken from UN Commodity Trade Statistics (UN COMTRADE). The
data cover 31 years from 1980 to 2010, and 193 countries. We use SITC version 1
since this version covers the maximum number of observations compared to all
newer versions of SITC and all versions of HS code. However, with respect to Lao
PDR, COMTRADE only covers the period 1962–1974. Therefore we are not able to
estimate the coefficient of the country dummy for Lao PDR.
Regarding explanatory variables, real GDP and real GDP per capita are taken
from the World Development Indicators of the World Bank. Flight distance in
kilometres is used for the distance between the largest cities, and is calculated by the
World Atlas flight Mileage Calculator.9
In order to convert import and export values
to those in real terms, we use the US consumer price index from International
Financial Statistics of the International Monetary Fund. Table 6 shows the summary
statistics of the data.