Medical researcher: A survey of more than 1 million adults found that there was a greater frequency of illness among people who regularly slept at least 8 hours a night than among people who slept significantly less. This shows that mild sleep deprivation is not unhealthy and, in fact, probably bolsters the body' s defenses against illness. The reasoning in the medical researcher's argument is most vulnerable to criticism on the grounds that the argument ['concludes, from the claim that a certain phenomenon occurs and the claim that a certain condition is sufficient for that phenomenon to occur, that the condition also exists', 'takes for granted that there will be an observable correlation between two phenomena if either of those phenomena causally contributes to the other', 'fails to consider that even if a specific negative consequence is not associated with a given phenomenon, that phenomenon may have other negative consequences', 'fails to address the possibility that an observed correlation between two phenomena is due to another factor that causally contributes to both phenomena']