More than one in four sexual assaults occur after a woman has been drugged by her assailant, according to new Canadian research. The study, published in the Canadian Journal of Public Health, shows that the incidence of so-called ''date-rape drugging'' has increased dramatically in the past decade. It also reveals that the vast majority of those who are drugged, then raped, are teenagers aged 15 to 19. The study, conducted by a team led by Margaret McGregor of the Department of Family Practice at the University of British Columbia, is believed to be the first to measure the extent of...