Class 11th Statistics Census and Sample Methods of Collection of Data Notes

1. Census and Sample Inquiry

• Census Inquiry: A method in which data is collected from each and every unit of the population.
• Sample Inquiry: A method in which data is collected from a representative part (sample) of the population.

2. Census Method (Method of Complete Enumeration)

(a) Meaning

In the census method, information is collected from every unit of the population without leaving anyone.

(b) Suitability (5 points, one line each)

1. Suitable when population is small.
2. Used when high accuracy is required.
3. Applied in government population census.
4. Best for heterogeneous population.
5. Suitable when sufficient resources (time, money, staff) are available.

(c) Advantages (Merits)

1. Provides complete information.
2. More accurate and reliable.
3. Useful for diverse population.
4. Data available for different characteristics.
5. Basis for sample surveys.

(d) Disadvantages (Demerits)

1. Very costly.
2. Time-consuming.
3. Requires large manpower.
4. Not suitable for large populations.
5. Difficult to maintain secrecy and accuracy.

3. Sample Method

(a) Meaning

In the sample method, information is collected from a small representative group (sample) of the population, and results are generalized for the whole.

(b) Suitability (5 points)

1. Best for large populations.
2. When time and money are limited.
3. When quick decisions are needed.
4. When population is homogeneous.
5. Suitable for scientific research.

(c) Advantages (Merits)

1. Economical and less costly.
2. Saves time and energy.
3. Requires fewer investigators.
4. Suitable for large population.
5. Scientific and more practicable.

(d) Disadvantages (Demerits)

1. Not suitable for heterogeneous population.
2. Chance of sampling error.
3. May not be accurate always.
4. Results depend on representativeness of sample.
5. Bias may affect the results.

4. Essentials / Qualities of a Good Sample

1. Representativeness – Must represent the population truly.
2. Independence – Selection of one unit should not affect others.
3. Homogeneity – Characteristics of sample should match the population.
4. Adequacy – Sample size should be sufficient for accuracy.

5. Methods of Sampling

(a) Random Sampling

• Meaning: Each unit of the population has an equal chance of being selected.

Ways:

1. Lottery Method: Names/numbers written on slips and drawn randomly.
2. Tables of Random Numbers: Pre-prepared random number tables used for selection.

Merits:

1. Simple to understand.
2. Free from personal bias.
3. Equal chance to all units.
4. Representative in nature.
5. Scientific and objective.

Demerits:

1. Needs complete list of population.
2. Costly if population is large.
3. Sometimes unrepresentative sample may be selected.
4. Difficult in scattered population.
5. Requires careful planning.

(b) Non-Random Sampling

(i) Purposive or Deliberate Sampling

• Meaning: Investigator deliberately selects units which he considers typical.

Merits:

1. Simple and convenient.
2. Less costly.
3. Saves time.
4. Useful when experts are available.
5. Suitable for specialized studies.

Demerits:

1. Investigator’s bias.
2. Not truly representative.
3. Accuracy doubtful.
4. Less scientific.
5. Not suitable for generalizations.

(ii) Stratified / Mixed Sampling

• Meaning: Population divided into groups (strata) and samples taken from each group.

Merits:

1. More representative.
2. Greater accuracy.
3. Useful for heterogeneous population.
4. Comparisons possible between strata.
5. Less chance of bias.

Demerits:

1. Requires classification of population.
2. More expensive than simple random sampling.
3. Complex in nature.
4. Errors possible in dividing strata.
5. Requires skilled investigators.

(iii) Systematic Sampling

• Meaning: Units selected at regular intervals from ordered population list.

Merits:

1. Simple and easy.
2. Saves time and money.
3. More representative than purposive.
4. Easy to administer.
5. Useful in large-scale surveys.

Demerits:

1. List of population required.
2. Periodicity may lead to bias.
3. Not truly random.
4. Accuracy doubtful sometimes.
5. Less scientific than pure random sampling.

(iv) Quota Sampling

• Meaning: Population divided into groups and fixed quota taken from each.

Merits:

1. Simple and convenient.
2. Less costly.
3. Saves time.
4. Ensures representation of groups.
5. Useful for opinion surveys.

Demerits:

1. Investigator’s bias.
2. Not random in nature.
3. Accuracy doubtful.
4. Not suitable for large population.
5. Less scientific.

(v) Convenience Sampling

• Meaning: Samples selected according to convenience of investigator.

Merits:

1. Very easy.
2. Saves time and money.
3. Useful for preliminary studies.
4. Requires less planning.
5. Convenient when population is scattered.

Demerits:

1. Highly biased.
2. Not representative.
3. Accuracy doubtful.
4. Unscientific method.
5. Not suitable for serious studies.

6. Reliability of Sampling Data

• Sampling results are reliable if:

1. Sample is representative.
2. Sample size is adequate.
3. Method of sampling is scientific.
4. Trained investigators are used.
5. Errors are minimized.

7. Difference Between Census and Sampling Method