ولﻻطﻻع على موجز للقيود التي عانت منها مختلف الدراسات، انظر Congress of the United States, Office of Technology Assessment (OTA), Trade and Environment: Conflicts and Opportunities.
Резюме проблем, возникавших при проведении различных исследований, см.: Congress of the United States, Office of Technology Assessment (OTA), Trade and Environment: Conflicts and Opportunities.