The next set of variables reflects trade constraining factors. Basically, these factors can be
classified into artificial barriers and natural impediments to trade, respectively. These
components can, to a reasonable extent, be regarded as total costs of transactions, which
include, among others, costs of transaction, distance between trading partners, trade policies
(e.g. nominal tariff rates on imports from country i by country j) and non-tariff barriers to trade
such as import restriction, import licensing, foreign exchange rationing, just to mention a few
(Ogunkola 1998). Some of these variables can be quantified while others are qualitative.