During an influenza outbreak in a large hospital, infection control officers compare the incidence of laboratory-confirmed influenza among non–health-care–worker volunteers who are unvaccinated (exposed) versus vaccinated (nonexposed). Among 200 unvaccinated volunteers followed for the season, 20 develop influenza. Among 300 vaccinated volunteers, 6 develop influenza. Calculate the attributable risk percent (AR%) among the unvaccinated group attributable to lack of vaccination.