A study covering clinical research in the 1980–90s found that only 21.5% of drug candidates that started Phase I trials were eventually approved for marketing. During 2006–15, the success rate of obtaining approval from Phase I to successful Phase III trials was under 10% on average, and 16% specifically for vaccines. The high failure rates associated with pharmaceutical development are referred to as an "attrition rate", requiring decisions during the early stages of drug development to "kill" projects early to avoid costly failures.