A fourth peer-reviewed study — by Harvard public health researcher Janet Rosenbaum published in the American Journal of Public Health in June 2006 — found that over half of adolescents who took virginity pledges said the following year that they had never taken a pledge. This study showed that those who make the pledge but have sex are likely to deny ever pledging; and many who were sexually active prior to taking the pledge deny their sexual history, which, it is speculated, may cause them to underestimate their risk of having STIs.