This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
[{'content': 'Which one of the following is a better indicator for calculating the severity of an acute disease? \nSelect and explain. \nA. Cause specific death rate, B. Case fatality rate, C. Standardized mortality ratio, D. Five year survival rate', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Case fatality rate represents the killing power of a disease.\xa0\nIt is\xa0 simply the\xa0 ratio of deaths to cases. The time interval is not specified.\xa0 Case\xa0 fatality\xa0 rate\xa0 is\xa0 typically\xa0 used\xa0 in\xa0 acute infectious diseases (e.g. , food\xa0 poisoning, cholera, measles). Its\xa0 usefulness\xa0 for\xa0 chronic\xa0 diseases\xa0 is\xa0 limited,\xa0 because\xa0 the period\xa0 from\xa0 onset to\xa0 death is\xa0 long and variable.\xa0 The\xa0 case fatality\xa0 rate\xa0 for\xa0 the\xa0 same\xa0 disease\xa0 may\xa0 vary\xa0 in\xa0 different epidemics\xa0 because\xa0 of\xa0 changes\xa0 in\xa0 the\xa0 agent,\xa0 host\xa0 and environmental\xa0 factors.\xa0 Case\xa0 fatality\xa0 is\xa0 closely\xa0 related\xa0 to virulence.', 'role': 'assistant'}]