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: Social & Preventive Medicine
Which of the following is the national level system that provides annual national as well as state level reliable estimates of fertility and mortality? 
Select and explain. 
A. Sample registration system, B. Census, C. Ad-hoc survey, D. Sample registration system
A: Sample registration system
Answer: A: Sample registration system 
Explanation: Sample Registration System (SRS) was initiated in 1964–65 (on a pilot basis; full scale from 1969–70) to provide national as well as state level reliable estimates of fertility and mortality
• SRS is a dual record system:
Field Investigation: continuous enumeration of births and deaths by an enumerator.
Independent retrospective survey: every 6 months by an investigator-supervisor.