In this PPT I have explained the collection of data topic for class 11 students. Teachers can use it as a teaching aid.

1. Collection of Data
Statistics
Class - XI

2. Synopsis
1. Key terms
2. Sources of data
3. Surveys
4. Census or complete Enumeration
5. Sample survey
6. Questionnaire
7. Types of questions
8. Open ended Vs Close ended
9. Mode of data collection
10. Pilot survey
11. Methods of sampling
12. Important agencies

3. Key Terms
Variable: The values which change, such as production of food grains
per annum, temperature of a city, etc. They are represented by the
letters X,Y or Z.
Observation: The value of an variable.
Data: Observations corresponding to different variables.
Statistical Investigation: It means search for information conducted by
using statistical methods.

4. Key Terms
Investigators: The person who
conducts statistical investigation.
Enumerators: A person who helps
investigator in the collection of data.
Respondents: The persons from
whom statistical information is
collected.
Statistical Unit: The items on which
measurements are taken. Example;
weight in kgs.

5. Population or the Universe: it
means totality of the items under
study.
Sample: It refers to a group or
section of the population from
which information is to be
obtained.
Good sample: It is smaller than
the population and is capable of
providing accurate information
about the population at lower
cost and lesser time.
Key Terms

6. Sources of Data
1. Primary Data: when the enumerator collect the data by
conducting an enquiry or an investigation. They are based on
first hand information.
For example, you will have to enquire from a large number
of school students, by asking questions from them to collect
the desired information.
2. Secondary Data: When the data have been collected and
processed by some other agency. It is based on second hand
information.
For example, information obtained from publish sources
such as government reports, newspaper.

7. Surveys
Survey is a method of gathering information from
individuals. The surveys are done to describe some
characteristics like price, quality, usefulness and popularity,
etc.
The purpose is to collect data.
On the basis of area covered there are two methods of
survey:
1. Census Survey
2. Sample Survey

8. Census or Complete Enumeration
A survey which includes every element of the population. It
covers every individual unit in the entire population. The
example includes Census of India, which is carried out every ten
years. This surveys are carried for demographic data on birth,
death, literacy.
Advantages Disadvantages
Results are absolutely correct,
accurate and reliable
A lot of time, energy and money is
required to collect data
Less chances of biasness Suitable for certain specific cases
Data related to each element is
collected
Large number of enumerators are
required for collecting data

9. Sample Survey
In this a sample from the population is surveyed. The first step is
selecting a sample to identify the population. Than select
Representative Sample, as it is difficult to study entire
population.
Example: Population, research, etc.
Advantages Disadvantages
Economical as only some units are
studied
Partial investigation of the universe
Not time consuming
Not easy to select a sample which
represent whole population
Less efforts are required as small
portion is studied
It is complicated process and
difficult

10. Questionnaire
The most common type of instrument used in surveys for
collecting primary data is questionnaire.
While preparing the same the following points are kept in mind:
• It should not be too long
• The series of questions should move from general to specific
• The questions should be precise and clear
• The questions should not be ambiguous
• The question should not use double negatives
• The question should not be a leading question
• The question should not indicate alternatives to the answer

11. Types of Questions in Questionnaire
1. Closed ended or structured questions: It could be a
two-way question or a multiple choice question. When
there are only 2 possible answers it is called a two way
question. When there is a possibility of more than 2
answers it is called multiple choice question.
2. Open ended or unstructured questions: It could be
descriptive types. When a person gets a chance to talk
more about any topic.

12. Differentiate Close Ended Versus
Open Ended
Closed Ended Question Open Ended Question
Easier to compare responses Detailed and qualifies responses
Quicker and easier answers Unlimited possible answers
Easy to interpret Difficult to interpret
Easy to score Difficult to score
Easy to codify for analysis Difficult to codify for analysis
Example: Do you smoke?
Example: What is your view about
globalization?

13. Mode of Data Collection
1. Personal Interviews: In this method, The investigator
conducts interviews with the respondents and obtained
required information.
Two types of interview are:
• Direct Personal Interview: Investigator conducts face to
face interview with respondent.
• Indirect Personal Interview: Data is collected by
interviewing third person who are directly or indirectly
concerned with the subject matter of enquiry, they are
witness to the situation.

14. Personal Interviews
Advantages Disadvantages
High degree of originality Costly and time consuming
Information is reliable
Cannot be used where area of study
is large
Easy to administer Highly prone to personal biasness
Elastic method as necessary
adjustments in the set of questions
can be made
It requires that the investigator is
skilled and trained

15. Mode of Data Collection
2. Telephone Interviews: In this method, the investigator asks
questions over the telephone.
Advantages Disadvantages
Cheaper and takes shorter time Obstruct visual reactions.
They allow researcher to assist
respondents by clarifying questions
Excludes the population who are not
having telephone connection.
Helpful where respondents are
reluctant to answer questions in
personal interview.

16. Mode of Data Collection
3. Mailing Questionnaire: In this method, the required data
are collected by mail. The questionnaire is sent to each
respondent by mail with a request to complete and return it
by a given date.
Advantages Disadvantages
Less expensive
Possibility of misunderstanding the
questions
Allows access to researchers in
remote areas.
Produces low response rate
Allows respondents to take sufficient
time to answers
Data are not reliable

17. Mode of Data Collection

18. Pilot Survey/ Pre- Testing
It is a trial survey which helps to test the effectiveness of
the questionnaire on a small group.
Importance:
1. it helps in pre-testing of the questionnaire, so as to
know the shortcomings and drawbacks of the
questions.
2. It also helps in accessing the suitability of questions,
clarity of instructions, performance of enumerators and
cost and time involved.

19. Methods Of Sampling
1. Random Sampling: Method where samples are selected at
random. In this method, every individual unit has an equal
chance of being selected. Methods under random sampling:
a) Lottery Method: In this method all the items in the
populations are assigned a distinct number and these are
written on identical piece of paper and put in a bowl.
Samples are selected on random.
b) Table of Random Numbers: In this random numbers are
arranged in rows and column which are selected on
population size.
c) Exit Polls: it is used to predict election results. In this
technique a random sample of voters, who exit from the
polling booths are asked who they voted for.

20. 2. Non-Random Sampling: In this all the units of the
population do not have an equal chance of being selected.
Methods under this are:
a) Judgement/Purposive/Deliberate Sampling: Here
sample units are selected consciously by the investigator
on the basis of his judgement. This method is subject to
personal bias of investigator.
b) Quota Sampling: Here the investigator is allotted definite
quota and he is required to collect the required data from
a specific numbers of unit of each quota.
c) Convenience Sampling: Here the investigator collects the
sample units on the basis of his convenience.
Methods Of Sampling

21. Sampling and Non Sampling Errors
Error in statistics is used to denote the difference between the
true value and the estimated value. Errors can be classified as:
1. Sampling Errors: the difference between the actual value of
a parameter of the population( which is not known) and its
estimate( known). It is possible to reduce sampling error by
increasing the size of the sample.
2. Non- Sampling Errors: It includes:
• Errors in Data Acquisition: From recording incorrect
response
• Non-Response: It occurs when interviewer is unable to
contact person listed in the sample
• Sampling Bias: It occurs when in a sampling plan some
members of target population could not included

22. Important Agencies of Secondary Data
1.Census of India: It provides the
most important and complete
demographic record of population.
These are conducted every 10
years. The census official collects
information on various aspects of
population such as sex ratio,
literacy, migration, etc.
Which are used to interpret and
analyse to understand many
economic and social issues in India
and accordingly plans and policies
are formulated.

23. 2.National Sample Survey
Organisation: it was
established in 1950 under the
Ministry of Finance to
conduct surveys and collect
data on estimates of literacy,
school enrolments,
maternity, PDS, etc to publish
surveys through reports.
NSSO conducts continuous
surveys on various problems
in successive rounds.
Important Agencies of Secondary Data

24. Thank You!
Lesson by
Anjali Kaur Suri
TGT Maths, PGT Economics
M.A. Economics, M.Com (Finance), PGD Banking & Finance, B.A. Hons (Economics), B.Ed
(Maths & SST), NISM, NSDL and IELTS certified.
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