This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Demography and family planning, Subject name: Social & Preventive Medicine
[{'content': 'In calculating crude bih rate which of the following is used as denominator \nSelect and explain. \nA. Women in 15-49 yrs age group, B. All persons in 15-49 yrs age group, C. Mid year population, D. All live bihs', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Bih rate = Number of live bihs during the year X 1000 / Estimated mid year population Unsatisfactory measure of feility because the total population is not exposed to child bearing Reference : Park&;s textbook of preventive and social medicine, 23rd edition, pg no: 488', 'role': 'assistant'}]