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According to one study, people who went 17 to 19 hours without sleep performed as badly or worse on tests than when they had a blood alcohol content of 0.05 percent. Their response speeds during testing were reduced by up to 50 percent in some cases and their accuracy scores were significantly worse than when they had drunk. Furthermore, Knutson says that people are generally not very good at assessing how impaired we are by sleep loss. In sleep studies, she has found no relationship between how people say they feel and how they perform on tests.