The advent of AIDS helped build a more favorable view of abstinence. However, a review of 13 U.S. sex-abstinence programs involving over 15,000 people by Oxford University found that they do not stop risky sexual behavior, or help in the prevention of unwanted pregnancy. Other studies have found that abstinence-only education does little to affect the "age of sexual initiation; number of sexual partners; and rates of sexual abstinence, condom use, vaginal sex, pregnancy, and sexually transmitted infections (STIs)". Recently, the United States Congress also found similar results in a study conducted by Mathematica Policy Research on abstinence. Currently, there are also issues as to what abstinence means: is it an abstinence from sexual intercourse, or from sexual behavior? Movements such as True Love Waits in America, which ask teenagers to refrain from sex before marriage, are heavily subscribed, but surveys of sexual behavior indicate an increase in the popularity of oral sex.