Studies of trade in services use general explanatory factors of export performance: GDP, exchange rates and internet adoption (Freund and Weinhold 2002). Kimura and Lee (2006) show that the important workhorse in empirical international economics being the gravity equation also works surprisingly well (even better than mirror samples for manufacturing) towards explaining trade in services. According to Kimura and Lee’s (2006) study, distance is a highly significant negative factor preventing service trade. Mirza and Nicoletti (2004) report similar results but give other explanations besides physical distance for why gravity type of equations work particularly well in services related with the o-ring theory of development (Kremer 1993).