2. Sampling is the process of selecting observations
(a sample) to provide an adequate description
and inferences of the population.
◾ Sample
⦿ It is a unit that is selected from
population
⦿ Represents the whole population
⦿ Purpose to draw the inference
◾ Why Sample???
◾ Sampling Frame
Listing of population from which
8. ⦿ All subsets of the frame are given an
equal probability.
⦿ Random number generators
9. Advantages:
⦿ Minimal knowledge of
population needed
⦿ Easy to analyze data
Disadvantages:
⦿ Low frequency of use
⦿ Does not use
researchers’ expertise
⦿ Larger risk of random
error
10. ⦿ Population is divided into two or more
groups called strata
⦿ Subsamples are randomly selected from
each strata
11. Advantages:
⦿ Assures representation of all groups
in sample population
⦿ Characteristics of each stratum can
be estimated and comparisons made
Disadvantages:
⦿ Requires accurate information
on proportions of each stratum
⦿ Stratified lists costly to prepare
12. ⦿ The population is divided into subgroups (clusters)
like families.
⦿ A simple random sample is taken from each cluster
13. Advantages:
⦿ Can estimate characteristics of both
cluster and population
Disadvantages:
⦿ The cost to reach an element to sample
is very high
⦿ Each stage in cluster sampling
introduces sampling error—the more
stages there are, the more error there
tends to be
14. ⦿ Order all units in the sampling frame
⦿ Then every nth number on the list is
selected
⦿ N= Sampling Interval
16. ⦿ Carried out in stages
⦿ Using smaller and smaller sampling units at
each
stage
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2
3
4
5
6
7
8
9
1 0
P r i m a r y
C l u s t e r s
1
2
3
4
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6
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8
9
1 0
1 1
1 2
1 3
1 4
1 5
S e c o n d a r y
C l u s t e r s S i m p l e R a n d o m S a m p l i n g w i t h i
n
S e c o n d a
17. Advantages:
⦿ More Accurate
⦿ More Effective
Disadvantages:
⦿ Costly
⦿ Each stage in sampling introduces sampling
error—the more stages there are, the more
error there tends to be
19. ⦿ The probability of each case being selected from
the total population is not known.
⦿ Units of the sample are chosen on the basis
of personal judgment or convenience.
⦿ There are NO statistical techniques for measuring
random sampling error in a non-probability sample.
20. ⦿ A. Convenience Sampling
⦿ B. Quota Sampling
⦿ C. Judgmental Sampling (Purposive
Sampling)
⦿ D. Snowball sampling
⦿ E. Self-selection sampling
21. ⦿ Convenience sampling involves choosing respondents
at the convenience of the researcher.
Advantages
⦿ Very low cost
⦿ Extensively used/understood
Disadvantages
⦿ Variability and bias cannot be measured or
controlled
⦿ Projecting data beyond sample not justified
⦿ Restriction of Generalization.
23. ⦿ The population is first segmented into mutually
exclusive sub-groups, just as in stratified sampling.
Advantages
⦿ Used when research budget is limited
⦿ Very extensively used/understood
⦿ No need for list of population elements
Disadvantages
⦿ Variability and bias cannot be
measured/controlled
⦿ Time Consuming
24. ⦿ Researcher employs his or her own
"expert” judgment about.
Advantages
⦿ There is a assurance of Quality response
⦿ Meet the specific objective.
Disadvantages
⦿ Bias selection of sample may occur
⦿ Time consuming process.
25. ⦿ The research starts with a key person
and introduce the next one to become a
chain
Advantages
⦿ Low cost
⦿ Useful in specific circumstances & for locating rare
populations
Disadvantages
⦿ Not independent
⦿ Projecting data beyond sample not justified
26. ⦿ It occurs when you allow each case usually
individuals, to identify their desire to take part in the
research.
Advantages
⦿ More accurate
⦿ Useful in specific circumstances to serve the
purpose.
Disadvantages
⦿ More costly due to Advertizing
⦿ Mass are left
28. ⦿ The errors which arise due to the use of
sampling surveys are known as the sampling
errors.
Two types of sampling errors
⦿ Biased Errors- Due to selection of
sampling techniques; size of the sample.
⦿ Unbiased Errors / Random sampling
errors- Differences between the members
of the population included or not included.
29. ⦿ Specific problem selection.
⦿ Systematic documentation of related
research.
⦿ Effective enumeration.
⦿ Effective pre testing.
⦿ Controlling methodological bias.
⦿ Selection of appropriate sampling techniques.
30. ⦿ Non-sampling errors refers to biases
and mistakes in selection of sample.
⦿ CAUSES FOR NON-SAMPLING ERRORS
Sampling operations
Inadequate of response
Misunderstanding the concept
Lack of knowledge
Concealment of the truth.
Loaded questions
Processing errors
Sample size
