is the most important selection criteria for the various post season invitation rowing championships. If the crew is in a league, the dual race and regatta results will also typically be used in determining the team's seeding for the league championship. The Dad Vail Regatta is the largest and most prestigious for smaller schools and is held every May in Philadelphia. The lightweight division becomes more prominent during the spring. Many head races lack separate categories for heavyweight/lightweight, but many spring races have a separate weight category for lighter rowers. National championships Men's The Intercollegiate Rowing Association, known as the IRA, was founded by Cornell, Columbia, and Penn in 1894 and its first annual regatta was hosted on June 24, 1895. Today Navy and Syracuse are also members of the association. Each year these five schools choose whom to invite to the regatta and are responsible for its organization along with the ECAC. The IRA is the oldest college rowing championship in the United States. Since the 1920s, when the West Coast crews, notably California and University of Washington began to attend and regularly win, most crews considered the Intercollegiate Rowing Association's championship to be a de facto national championship. Two important crews, Harvard and Yale, however, did not participate in the heavyweight divisions of the event. After losing to Cornell in 1897, Harvard and Yale chose to avoid the IRA, so as not to diminish the Harvard-Yale race. It soon became part of each school's tradition not to go. Beginning in 1973, Washington decided to skip the IRA because a change in schedule conflicted with its finals. Even though rowing is the oldest intercollegiate sport, the men have always chosen not to join the NCAA. If they did, the NCAA would sponsor a championship, but it would also force the sport to abide by NCAA rules and mandates. Notwithstanding, collegiate crews generally abide by NCAA rules, and they also have to abide by athletic conference rules, which mirror the NCAA rules. In 1982, a Harvard alumnus decided to remedy this perceived problem by establishing a heavyweight varsity National Collegiate Rowing Championship race in Cincinnati, Ohio. It paid for the winners of the Pac-10 Championship, the Eastern Sprints, the IRA and the Harvard-Yale race to attend. It was a finals only event and other crews could attend if they paid their own way and there was room in the field.