6 As noted by Brenton (2003), in the case of preferential exports to the EU, these compliance costs will tend to be particularly high if the good is not shipped directly to the EU, because there are very strict rules concerning transit through other countries, and it is difficult to provide the necessary documentation to prove that these transit rules have been followed. This is particularly relevant for developing countries, for which transit through other countries is often necessary.
7 It is sometimes argued that rules of origin may be deliberately used as a trade barrier – for an early discussion of this, see e.g. Krueger (1997). Lending some support to this notion, Cadot et al. (2006), using a restrictiveness index to capture the cost-raising potential of rules of origin at the tariff-line level, find evidence that rules of origin are more restrictive in sectors that also have high MFN tariffs.