Home › Free notes › Class 11 Economics › Collection of Data

Collection of Data – Class 11 Economics notes, important questions and MCQs

NCERT Class 11 Economics, chapter 2. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Data are the raw material of statistics. Data may be primary, collected first-hand by the investigator, or secondary, already collected by someone else. Data are collected through surveys using interviews or questionnaires, either from every unit (census) or from a part of the population (sample). Errors can creep in at every stage and must be minimised.

Primary and secondary data

Primary data are original data collected by the investigator for a specific purpose.
Secondary data are collected from published or unpublished sources such as government reports.
Primary data are more reliable for the purpose but cost more time and money.

Methods of collection

Personal interview: the investigator asks questions face to face; it gives high response but is costly.
Mailing questionnaire: questions are sent by post or email; it is cheap but the response rate may be low.
Telephone interview: quick and cheaper, but people without phones are left out.
A good questionnaire is short, clear, in logical order and avoids leading questions; a pilot survey tests it first.

Census, sample and errors

A census survey covers every unit of the population; the Census of India counts the whole population.
A sample survey covers a representative part; in random sampling every unit has an equal chance of selection.
Sampling error is the difference between the sample estimate and the true value; non-sampling errors arise from measurement, non-response or recording mistakes.
The National Sample Survey Office, now part of the National Statistical Office, conducts large sample surveys in India.

Key terms

Primary data: data collected first-hand by the investigator for a specific purpose
Secondary data: data already collected by someone else and used by the investigator
Population (statistics): the total group of all units about which information is required
Random sampling: a method in which every unit of the population has an equal chance of being selected
Pilot survey: a small trial survey done to test the questionnaire before the main survey

Important questions with answers

Distinguish between primary and secondary data.2 marks

Primary data are original data collected first-hand by the investigator for a specific purpose, for example through a survey. Secondary data are data already collected by another person or agency, such as a government report, and used by the investigator.

What are the qualities of a good questionnaire?3 marks

A good questionnaire is short, with simple and clear questions arranged in a logical order from general to specific. It avoids leading questions, ambiguous words, personal or embarrassing questions and calculations. Questions should be precise, preferably with options, and the questionnaire should be tested through a pilot survey.

Compare the census method and the sample method of collecting data. Why is the sample method more commonly used?5 marks

In the census method, data are collected from every unit of the population, for example the Census of India, which counts every person. It gives complete and accurate information about each unit and is suitable when the population is small or when complete information is needed. However, it is very costly, needs a large staff and takes a long time. In the sample method, data are collected from a representative part of the population, chosen for example by random sampling, in which every unit has an equal chance of selection, and the results are applied to the whole population. It saves time, money and labour, can be conducted more carefully by trained staff, and is the only option when units are destroyed in testing. It has sampling error, but this can be reduced by taking a larger, well-chosen sample. Non-sampling errors such as measurement and non-response errors may occur in both methods and are often fewer in a sample survey. For these reasons, the sample method is more commonly used, for example by the National Statistical Office in India.

Quick revision

Primary = first-hand; secondary = already collected.
Interview, mail questionnaire, telephone.
Census vs sample; random sampling.
Sampling and non-sampling errors.

Exam tips

Make a table of merits and demerits of each method of data collection.
Remember: census = every unit; sample = part of units.

Practice MCQs

Data collected first-hand by the investigator are
1. secondary data
2. published data
3. primary data
4. old data
Show answer
Answer: (c) primary data. They are original.
A survey that covers every unit of the population is a
1. sample survey
2. pilot survey
3. census survey
4. random survey
Show answer
Answer: (c) census survey. The Census of India is an example.
Data taken from a government report are
1. secondary data
2. primary data
3. qualitative only
4. errors
Show answer
Answer: (a) secondary data. Someone else collected them.
In random sampling, every unit of the population has
1. no chance of selection
2. a fixed order
3. an equal chance of selection
4. a higher chance if rich
Show answer
Answer: (c) an equal chance of selection. It avoids bias.
A small trial survey to test a questionnaire is a
1. pilot survey
2. census
3. final survey
4. sampling error
Show answer
Answer: (a) pilot survey. It shows problems in questions.
Which method of collection usually gives the lowest response rate
1. personal interview
2. telephone interview
3. observation
4. mailing questionnaire
Show answer
Answer: (d) mailing questionnaire. Many people do not return forms.
The difference between a sample estimate and the true population value is called
1. non-sampling error
2. response error
3. recording error
4. sampling error
Show answer
Answer: (d) sampling error. It can be reduced by taking a larger sample.
Which is a non-sampling error
1. difference due to small sample size
2. using a census
3. a perfectly random sample
4. mistakes in recording answers
Show answer
Answer: (d) mistakes in recording answers. It can occur even in a census.

All chapters of Class 11 Economics

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.