Q. What is the difference between Census and Sample Surveys in Official Statistics, and why does India still conduct a Population Census every 10 years despite having large-scale surveys like NSSO and

Q. What is the difference between Census and Sample Surveys in Official Statistics, and why does India still conduct a Population Census every 10 years despite having large-scale surveys like NSSO and NFHS?

✅ Answer

A Census is a complete enumeration of the entire population. Every individual and household is covered, and information is collected on multiple aspects such as demographic details, housing, literacy, occupation, etc. In India, the Population Census is conducted once every ten years under the Census Act, 1948.

A Sample Survey, on the other hand, is based on a scientifically chosen subset of the population, selected through probability sampling. It is cheaper, quicker, and easier to conduct compared to a Census, but its estimates are subject to sampling errors (though these can be measured and controlled statistically). Examples include NSSO household surveys, NFHS (National Family Health Survey), and PLFS (Periodic Labour Force Survey).

Now, one may wonder: If surveys can give us timely and cost-effective data, why do we still need a Census?

The answer lies in the unique advantages of the Census:

1. Benchmarking: Census provides the frame population for weights used in all surveys. Without it, survey estimates cannot be properly scaled.

2. Small-Area Statistics: Surveys cannot give reliable data for small units like villages, wards, and towns. Census data is indispensable for micro-level planning (like school or hospital location).

3. Policy and Administrative Uses: Census data underpins electoral rolls, delimitation of constituencies, reservation policies, allocation of central funds, and local governance decisions.

4. Population Projections: Base year Census provides denominators for fertility, mortality, and migration estimates used in projections.

5. International Obligation: The UN recommends every country to conduct a Census at least once in 10 years for comparability of global demographic indicators.

Thus, Census and Surveys are complementary, not substitutes. Surveys fill the gap between Censuses, while Census remains the foundational database.

🔄 Cross Questions with Answers

CQ1. If Census is conducted only once in 10 years, how do planners get updated population estimates in between?

• Answer: They rely on population projection methods such as the cohort-component method (which accounts for fertility, mortality, migration), exponential and logistic projections. These projections are updated using sample surveys (like SRS for birth and death rates) and administrative records (Civil Registration System, school enrollment data, voter lists, etc.). This ensures that estimates remain close to reality until the next Census.

CQ2. What practical challenges did India face in conducting Census 2021?

• Answer: The biggest disruption was the COVID-19 pandemic, which made large-scale fieldwork impossible. Further challenges included:

  • Transition to digital data collection for the first time, requiring new infrastructure and training.

  • Concerns about data privacy and confidentiality with digital enumeration.

  • Enumerator training and recruitment on a massive scale.

  • Increased costs and logistical issues in covering over 1.3 billion people. Because of these challenges, the 2021 Census has been indefinitely postponed, creating gaps in the statistical system.

CQ3. (Situational/Practical) Suppose you are in charge of an NSSO survey, and you find that weights based on the 2011 Census no longer reflect reality due to migration and urbanization. What would you do?

• Answer:

  1. Use inter-censal projections of population by age, sex, and rural/urban categories.

  2. Apply post-stratification techniques, adjusting sample weights to align with the latest projected population structure.

  3. Incorporate administrative data sources (Aadhaar, school enrollments, EPFO/ESIC) to improve representativeness.

  4. Clearly document the methodology in technical reports to ensure transparency and credibility of estimates.

🧩 Key Takeaway

• Census = complete, benchmark, micro-level data, but costly and infrequent.

• Sample Surveys = quicker, cheaper, but dependent on Census for calibration.

• India continues to conduct a Census every 10 years because no survey can fully replace its comprehensive role in governance, planning, and international comparability.