Class 11 Statistics for Economics Chapter 2: Collection of Data

Introduction

Data collection is the first step in any statistical investigation. Data helps us understand a problem, analyze it, and arrive at logical conclusions.

Meaning of Data

Data refers to facts and figures collected for a specific purpose.

Importance of Data

Helps in understanding economic problems.
Assists in decision-making.
Provides evidence for conclusions.
Helps formulate policies and plans.

Variable and Observation

Variable

A characteristic whose value changes from one unit to another is called a variable.

Examples

Income
Marks
Age
Production

Variables are usually represented by:

Observation

Each value of a variable is called an observation.

Example

Year	Production (Million Tonnes)
2015	252
2016	272

Here, production is a variable and 252, 272 are observations.

Sources of Data

Statistical data are collected from two main sources:

1. Primary Data

Primary data are collected directly by the investigator for the first time.

Features

Original data
First-hand information
Collected for a specific purpose

Examples

Survey conducted by a researcher
Personal interview
Questionnaire responses

Advantages

More reliable
Relevant to the objective
Up-to-date

Disadvantages

Expensive
Time-consuming

2. Secondary Data

Secondary data are already collected and processed by another person or organization.

Sources

Government reports
Census reports
Books
Newspapers
Journals
Websites

Advantages

Saves time
Saves money
Easily available

Disadvantages

May be outdated
Reliability may vary

Methods of Data Collection

Survey is the most common method of collecting data.

Survey

A survey is a method of gathering information from individuals.

Questionnaire

A questionnaire is a list of questions used to collect information.

Qualities of a Good Questionnaire

1. Short and Simple

Questions should be brief and easy to understand.

2. Clear Language

Avoid difficult words.

3. Logical Order

Questions should move from general to specific.

4. Precise Questions

Questions should be specific.

5. Avoid Ambiguity

Questions should have clear meanings.

6. Avoid Double Negatives

Questions should not confuse respondents.

7. Avoid Leading Questions

Questions should not suggest answers.

8. Avoid Restricted Alternatives

Respondents should get sufficient choices.

Types of Questions

1. Open-Ended Questions

Respondents answer in their own words.

Example

What is your opinion about online education?

Advantages

Detailed responses
Freedom of expression

Disadvantages

Difficult to analyze
Time-consuming

2. Closed-Ended Questions

Answers are given from fixed alternatives.

Example

Do you use a computer?

(a) Yes
(b) No

Advantages

Easy to analyze
Easy to compare

Disadvantages

Limited responses

Types of Closed Questions

A. Two-Way Questions

Only two answers are possible.

Example

Do you watch television?

B. Multiple Choice Questions

Example

How much do you spend on books monthly?

Less than ₹200
₹200–₹300
₹300–₹400
More than ₹400

Modes of Data Collection

There are three major methods:

1. Personal Interview

The investigator meets respondents face-to-face.

Advantages

High response rate
Clarification possible
Suitable for open-ended questions

Disadvantages

Expensive
Time-consuming
Possibility of interviewer influence

2. Mailed Questionnaire

Questionnaires are sent through post, email, or online forms.

Advantages

Low cost
Suitable for large areas
No interviewer bias

Disadvantages

Low response rate
Misunderstanding possible
Delayed replies

3. Telephone Interview

Questions are asked over the phone.

Advantages

Quick
Less expensive
Clarification possible

Disadvantages

Limited coverage
Cannot observe reactions

Pilot Survey

A pilot survey is a trial survey conducted on a small group before the actual survey.

Objectives

Test questionnaire
Identify errors
Estimate cost and time
Improve survey quality

Importance

Helps avoid mistakes in the main survey.

Census and Sample Survey

Census Method

Census means collecting information from every unit of the population.

Features

Complete enumeration
Covers all units

Advantages

Highly accurate
Complete information

Disadvantages

Expensive
Time-consuming

Example

Population Census of India

Population

Population means the complete set of units under study.

Examples

All students in a school
All farmers in a district
All households in a village

Sample

A sample is a smaller group selected from the population.

Example

50 students selected from 500 students.

Features

Smaller in size
Represents the population

Sample Survey

Information is collected only from selected units.

Advantages

Less expensive
Faster
Easier supervision
More detailed study

Disadvantages

Possibility of errors

Sampling Methods

1. Random Sampling

Every unit has an equal chance of selection.

Example

Lottery Method

Features

Unbiased
Representative

Advantages

Fair selection
Reliable results

2. Non-Random Sampling

Selection depends on convenience or judgment.

Features

Unequal chance of selection
Investigator bias possible

Examples

Convenience sampling
Judgment sampling

Disadvantage

May not represent the population properly.

Sampling Errors

Meaning

Difference between sample results and actual population values.

Causes

Small sample size
Improper selection

Reduction

Can be reduced by increasing sample size.

Non-Sampling Errors

These errors occur even in Census studies.

Types

1. Sampling Bias

Some population members are excluded.

2. Non-Response Error

Respondents refuse or fail to answer.

3. Data Acquisition Error

Incorrect recording or measurement.

Examples

Recording 13 instead of 31
Wrong measurement of length

Important Point

Non-sampling errors are generally more serious than sampling errors.

Important Statistical Agencies in India

1. Census of India

Features

Conducted every 10 years
Provides demographic data

Information Collected

Population
Literacy
Sex ratio
Migration
Employment

Importance

Provides detailed information about India’s population.

2. National Sample Survey (NSS)

Established By

Government of India

Purpose

Conducts large-scale sample surveys.

Areas Covered

Employment
Unemployment
Consumer expenditure
Health
Education
Industrial activities

Importance

Provides data for economic planning.

Difference Between Primary and Secondary Data

Primary Data	Secondary Data
Original data	Already collected data
First-hand information	Second-hand information
Costly	Economical
Time-consuming	Saves time
More relevant	May be less relevant

Difference Between Census and Sample Survey

Census	Sample Survey
Studies all units	Studies selected units
More costly	Less costly
More time required	Less time required
More accurate	Less accurate but reliable
Suitable for small populations	Suitable for large populations

Difference Between Random and Non-Random Sampling

Random Sampling	Non-Random Sampling
Equal chance of selection	Unequal chance
Unbiased	Biased
Scientific method	Non-scientific
More representative	Less representative

Key Terms

Term	Meaning
Data	Facts and figures
Variable	Characteristic that changes
Observation	Individual value of a variable
Primary Data	First-hand data
Secondary Data	Previously collected data
Survey	Collection of information
Census	Study of every unit
Population	Entire group under study
Sample	Selected part of population
Random Sampling	Equal chance selection
Non-Random Sampling	Unequal chance selection
Sampling Error	Difference between sample and population value
Pilot Survey	Trial survey

Very Short Answer Questions (1 Mark)

1. What is data?

Answer: Data are facts and figures collected for a specific purpose.

2. What is a variable?

Answer: A variable is a characteristic whose value changes from one observation to another.

3. What is an observation?

Answer: Each value of a variable is called an observation.

4. What is primary data?

Answer: Data collected first-hand by the investigator for a specific purpose are called primary data.

5. What is secondary data?

Answer: Data already collected and processed by another person or agency are called secondary data.

6. What is a survey?

Answer: A survey is a method of collecting information from individuals.

7. What is a questionnaire?

Answer: A questionnaire is a list of questions used for collecting data.

8. What is a pilot survey?

Answer: A pilot survey is a trial survey conducted before the main survey.

9. What is Census?

Answer: Census is a method of collecting information from every unit of the population.

10. What is a sample?

Answer: A sample is a part of the population selected for study.

11. What is population?

Answer: Population is the complete group of units under study.

12. What is random sampling?

Answer: A sampling method where every unit has an equal chance of selection.

13. What is non-random sampling?

Answer: A sampling method where selection depends on judgment or convenience.

14. What is sampling error?

Answer: The difference between a sample estimate and the actual population value.

15. What is non-sampling error?

Answer: Errors that occur due to reasons other than sampling.

Short Answer Questions (3 Marks)

1. State any three characteristics of a good questionnaire.

Answer:

Questions should be simple and clear.
Questions should not be ambiguous.
Questions should be arranged logically.

2. Mention any three advantages of primary data.

Answer:

Original in nature.
More reliable.
Relevant to the objective of study.

3. Mention any three advantages of secondary data.

Answer:

Saves time.
Saves money.
Easily available.

4. What are open-ended questions?

Answer:
Open-ended questions allow respondents to answer in their own words without fixed alternatives.

Example:
What is your opinion about online education?

5. What are closed-ended questions?

Answer:
Closed-ended questions provide fixed alternatives for answers.

Example:
Do you use a smartphone?
(a) Yes
(b) No

6. Explain Personal Interview Method.

Answer:
In this method, the investigator meets respondents face-to-face and asks questions directly. It provides accurate information but is costly and time-consuming.

7. Explain Mailing Questionnaire Method.

Answer:
Questionnaires are sent through post, email, or online platforms. It is economical but may have low response rates.

8. Explain Telephone Interview Method.

Answer:
The investigator asks questions over the telephone. It is faster and cheaper than personal interviews but cannot reach people without telephones.

9. What is the importance of Pilot Survey?

Answer:

Tests the questionnaire.
Identifies mistakes.
Estimates cost and time.
Improves survey quality.

10. Why is sample survey preferred over census?

Answer:

Less costly.
Less time-consuming.
Easier supervision.
Suitable for large populations.

Long Answer Questions (5 Marks)

1. Differentiate between Primary Data and Secondary Data.

Primary Data	Secondary Data
Original data	Already collected data
First-hand information	Second-hand information
Costly	Less costly
Time-consuming	Saves time
More relevant	May be less relevant

2. Differentiate between Census and Sample Survey.

Census	Sample Survey
Studies all units	Studies selected units
More expensive	Less expensive
More time required	Less time required
More accurate	Relatively less accurate
Suitable for small populations	Suitable for large populations

3. Differentiate between Random and Non-Random Sampling.

Random Sampling	Non-Random Sampling
Equal chance of selection	Unequal chance
Unbiased	Biased
Scientific	Non-scientific
More representative	Less representative

4. Explain the advantages and disadvantages of Personal Interview.

Advantages

High response rate.
Clarification possible.
Suitable for detailed information.

Disadvantages

Expensive.
Time-consuming.
Interviewer bias may occur.

5. Explain the advantages and disadvantages of Mailed Questionnaire.

Advantages

Economical.
Suitable for large areas.
No interviewer influence.

Disadvantages

Low response rate.
Misunderstanding possible.
Delayed responses.

6. Explain Sampling Errors and Non-Sampling Errors.

Sampling Errors

Difference between sample estimate and population value.
Can be reduced by increasing sample size.

Non-Sampling Errors

Caused by recording mistakes, bias, or non-response.
Difficult to eliminate.

7. Explain the role of Census of India.

Answer:
The Census of India is conducted every ten years. It provides information on:

Population
Literacy
Sex ratio
Migration
Employment

It helps the government in planning and policy formulation.

8. Explain the role of NSS (National Sample Survey).

Answer:
NSS conducts nationwide sample surveys on:

Employment
Education
Health
Consumer expenditure
Industrial activities

The data are used for economic planning and policy making.

HOTS Questions

1. Why are non-sampling errors more serious than sampling errors?

Answer:
Because sampling errors can be reduced by increasing sample size, whereas non-sampling errors may occur even in a Census and are difficult to detect.

2. Why is a pilot survey conducted before the main survey?

Answer:
To identify weaknesses in the questionnaire and improve the quality of the actual survey.

3. Why should leading questions be avoided?

Answer:
Because they influence respondents and may produce biased answers.

Important Exam Questions

Define primary data and secondary data.
Explain the sources of data.
What is a questionnaire?
State the characteristics of a good questionnaire.
Explain personal interview, mailed questionnaire and telephone interview.
What is a pilot survey?
Differentiate between Census and Sample Survey.
Define population and sample with examples.
Explain random and non-random sampling.
Explain sampling and non-sampling errors.
What is the importance of Census of India?
Explain the role of National Sample Survey (NSS).
Why are sample surveys preferred in statistics?
Explain the advantages and disadvantages of different modes of data collection.