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Chapter 2
Sources of DataIbrahim Sameer (MBA - Specialized in Finance,
B.Com Specialized in Accounting & Marketing)
www.ibrahimsameer.wordpress.com
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Types of Data
Data may be classified as follows:
Primary
Secondary
Discrete
Continuous
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Types of Data
Primary data are data collected especially for a
specific purpose. Raw data are primary data
which have not been processed at all, and whichare still just a list of numbers.
For Eg: Telephone survey conduct by Dhiraagu to
monitor the effectiveness of the customer service.
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Types of Data
Secondary data are data which have already
been collected elsewhere, for some other
purpose, but which can be used or adapted for thesurvey being conducted.
Eg: Annual Statistics published by Department of
National Planning in the Maldives.
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Types of Data
Discrete data are data which can only taken on a
finite or countable number of values within a
given range. For example goals scored by Arsenal against
Chelsea in the FA cup final: Arsenal could score
0,1,2,3 or even 4 but they cannot score 1 or 2
goals.
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Types of Data
Continuous data are data which can take on any
values.They are measured rather than counted.
For example the heights of all members of yourfamily, as these can take on any value 1.542m,
1.696m, and 1.923m
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Types of Data
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Sources of Data
Data may be obtained from an internal sources or
an externalsources.
Internal data include such as accountinginformation, data relating to employees, much data
will be produced by a production department.
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Sources of Data
External data come in two form that is primary and
secondary data.
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Sources of Data
The main source of secondary data are:
government, banks, newspapers, trade
journals, information bureaux, consultancies,
libraries and information service.
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Sampling
Data are often collected from a samplerather than
from a population. If the whole population is
examined, the survey is called census.
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Sampling method
A probability sampling method is a sampling
method in which there is a known chance of each
memember of the population appearing in the
sample.
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Sampling method
Probability sampling methods include the
following:
Random
Stratified random
Systematic
Multistage
Cluster
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Sampling method
Random sampling
A simple random sample is a sample selected in
such a way that every item in the population hasan equal chance of being included.
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Sampling method
Sampling frames
If random sampling is used then it is necessary to
construct a sampling frame.
A sampling frame is a numbered list of all items
in a population. Sampling frame is required in
Random, Stratified random, Systematic, Multistage
& Cluster sampling.
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Sampling method
Drawback of Random sampling
An adequate sampling frame might not exist.
It might be costlyto obtain the data if the selected
items cover a wide range.
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Sampling method
Stratified random sampling
Stratified random sampling is a method of
sampling which involves dividing the populationinto strata or categories. Random samples are
then taken from each stratum or category.
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Sampling method
Advantages of Stratified random sampling
The samples selected will be representative.
The structure of the sample will reflect that of the
population.
Precisionis increased.
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Sampling method
Disadvantages of Stratified random sampling
Required prior knowledge of each item in the
population.
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Sampling method
Systematic sampling
Systematic sampling is a sampling method which
works by selecting every nth item after a random
start.
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Sampling method
Advantages of Systematic sampling
It is easy to use
It is cheap
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Sampling method
Disadvantages of Systematic sampling
It is possible that a biased sample might be
chosen if there is a regular pattern to the
population which coincides with the sampling
method.
It is not completely random since some items
have a zero chance of being selected.
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Sampling method
Multistage sampling
Multistage sampling is a probability sampling
method which involves dividing the population
into a number of sub-populations and then
selecting a small sample of these sub-population
at random.
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Sampling method
Advantages of Multistage sampling
Fewer investigators are needed.
It is not so costly to obtain a sample.
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Sampling method
Disadvantages of Multistage sampling
Possibility of bias
This method is not truly random.
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Sampling method
Cluster sampling
Cluster sampling is a non random sampling
method that involves selecting one definable
subsection of the population as the sample, the
subsection taken to be representative of the
population in question.
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Sampling method
For eg: the pupils of one school might be taken as
a cluster sample of all children at school in one
country.
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Sampling method
Advantages of Cluster sampling
It is a good alternative to multistage sampling if
a satisfactory sampling frame does not exist.
It is inexpensiveto operate.
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Sampling method
Disadvantages of Cluster sampling
There is potential for considerable bias.
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Sampling method
Non probability sampling method
A non probability sampling method is a sampling
method in which the chance of each member of
the population appearing in the sample is not
known.
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Sampling method
Quota sampling
In quota sampling, randomness is forfeited in the
interest of cheapness and administrative
simplicity. Investigators are told to interview all
the people they meet up to a certain quota.
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Sampling method
Advantages of Quota sampling
It is cheapand administratively easy
A much larger sample can be studied
No sampling frame is necessary
It yield enough accurateinformation
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Sampling method
Disadvantages of Quota sampling
Bias
Sampling error
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Questions & Answers
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Thank You
Ibrahim SameerSeek knowledge from cradle to grave