As noted in above, for travel and government services the same NTBTotal variable is used to measure restrictions in those sectors as no TRI is provided for these service sectors.29
For transport services, a more specific TRI measuring restrictions in maritime transport is used to proxy for NTBs in the transport sector as a whole. To supplement this measure, several coverage ratios from Hoekman (1995) were considered (maritime, air, land and total transport are among the sectors for which coverage ratios are provided). However, these measures are found to be poorly correlated with the TRI for transport and were not used.
To measure NTBs in commercial services, a TRI measuring restrictions in the banking sector is the primary source for the NTBComm variable. This sector is broader than simply banking and financial services but this TRI provides the closest match and it is reasonable to assume that banking and financial services provide a large share of the total value of commercial services. For a small number of countries for which a TRI is not provided, a coverage ratio for business and financial services is used (correlation coefficient of 0.76).
29 Hoekman (1995) provides a coverage ratio for education and health and social services but it is not clear from OECD (2003) that these sectors match the commodities included in the government services category.