Sample registration system is done once in-
**Core Concept**
The Sample Registration System (SRS) is a dual-record system used for estimating demographic and health indicators in India, involving continuous enumeration of births and deaths and a quarterly survey of a sample of households.
**Why the Correct Answer is Right**
The SRS is designed to provide accurate and reliable estimates of vital statistics, such as fertility rates, mortality rates, and population growth rates. It is conducted once every year to collect data on births, deaths, and migration. The data is collected through a continuous enumeration of events and a quarterly survey of a representative sample of households. This ensures that the estimates are based on a large and representative sample, thereby increasing the precision and reliability of the results.
**Why Each Wrong Option is Incorrect**
**Option A:** Not applicable, as the SRS is a continuous process with annual surveys.
**Option B:** Not applicable, as the SRS is not conducted every 6 months.
**Option C:** Not applicable, as the SRS is not conducted every 5 years.
**Clinical Pearl / High-Yield Fact**
The Sample Registration System is a vital tool for monitoring and evaluating the demographic and health trends in India, and its data is used to inform policy decisions and program planning.
**Correct Answer: D. Once a year.**