Researchers, therefore, recognized the need for well-controlled, multi-center studies to reliably demonstrate geographic variation in semen quality. In 1997, an international network of multi-center studies in Europe, the United States and Japan was begun to address this need. 

All these studies, following the model developed by the Danish researchers Skakkebaek and Jorgenson, studied semen quality in partners of pregnant women. These researchers have been committed to sharing study methods, quality control samples and data.