A 1974 WARN study reported that, during the 1970s, 40–50% of interviewed indigenous women believed they had been sterilized, although a subsequent study indicated this estimate was too high. Estimating the prevalence of sterilization is difficult, as the population did undergo growth during this period, while many of those who underwent the procedure already had three or four children.[5] As a result of the efforts of WARN to bring attention to these practices, in 1979 regulations governing sterilization were issued by the United States Department of Health and Human Services.[6] In 1980, WARN issued a report indicating a statistical correlation between the high levels of pollution on Pine Ridge Reservation and an increased incidence of birth defects, abortions and cancer. This region had been used for uranium mining, served as a military gunnery range and had been subjected to herbicide and insecticide contamination from off-reservation farms.[7]