The National Center for Health Statistics showed that teen birth rates in the United States are the lowest they have been since 60 years ago, when these statistics were first collected. Teen births have been dropping steadily over the past decade, and in 1999, for every 1,000 girls aged 15 to 19, there were 49.6 births in 1999. The most significant drop by age was among girls 15 to 17, whose rates fell 6 percent from 1998 to 28.7 births per 1,000. Rates fell across all racial lines, with a more significant drop among black teenagers, where the rate fell 38% from 1991 to 1999. Government demographers have credited a range of programs and organizations with the drop, including sex education programs, parents, churches, and abstinence groups. Others have also cited an increased fear of sexually transmitted diseases, the affect of AIDS, and the booming economy as factors in the drop.