2. Outlines
Sample definition
Purpose of sampling
Process in the selection of a sample
Types of sampling
Non probability sampling technique
3. Sampling is the process of selecting
observations (a sample) to provide an
adequate description and inferences of the
population.
4. What is Sampling?
Sampling is the act, process or technique of selecting a
suitable sample or a representative part of a population
for the purpose of determining parameters or
characteristics of the whole population
Suitable sample
5. Why Sampling instead of doing
a census?
Economy
Timeliness
Large size of population
Inaccessibility of some
population
Destructiveness of the
observation
Accuracy
10. Sampling criteria
Inclusion criteria- The criteria that specify population
characteristics
Exclusion Criteria- A population is defined in terms
of characteristics that people must
not possess
11. CONCEPTS OF SAMPLING
Target population
The aggregate of cases about which
Researcher would like to generalize
Whom do you wish to
generalize the findings?
Accessible population
The aggregate of cases conform
to designated criteria and that
are accessible
Which Population do
You have access?
Sampling Frame
The List or procedure defining the
Population (from which the sample
will be drawn)
E.g Telephone book ,Voters list
Through what resource
you can access them?
Sample
Subset of population elements
Who is participating
in your Study?
15. All subsets of the frame are given an
equal probability.
Random number generators
16. 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
17. Population is divided into two or more
groups called strata
Subsamples are randomly selected from each
strata
18. 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
19. The population is divided into subgroups (clusters) like
families.
A simple random sample is taken from each cluster
20. 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
21. Order all units in the sampling frame
Then every nth number on the list is selected
N= Sampling Interval
24. Carried out in stages
Using smaller and smaller sampling units at each
stage
Most commonly used sampling design in practice
Involves more than one stage of sampling and/or a
combination of two or more sampling designs
25. 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
26.
27.
28. 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.
30. Convenience sampling involves choosing
respondents
at the convenience of the researcher
.
31. 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.
32. • The population is first segmented into mutually exclusive sub-
groups, just as in stratified sampling.
• Judgment Used To Select Subjects From Each Segment
33.
34.
35. 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
Projecting data beyond sample
not justified
36. Researcher employs his or her own "expert”judgment
about.
Subjects are selected purposely who are judged to be
typical population and knowledgeable about the
issues
under the study
E.g. Home care of Diabetes mellitus, case studies
37. Advantages
There is a assurance of Quality
response
Meet the specific objective.
Disadvantages
Bias selection of sample may
occur
Time consuming process.
38. The research starts with a key person and introduce
the next one to become a chain Network or Chain
sampling
39. Advantages
Low cost
Useful in specific
circumstances & for locating
rare populations
Disadvantages
Not independent
Projecting data beyond sample
not justified
40. It occurs when you allow each case usually
individuals, to identify their desire to take part in the
research.
Select who volunteer for the sample
41. Advantages
More accurate
Useful in specific circumstances
to serve the purpose.
Disadvantages
More costly due to Advertizing
Mass are left
43. Sampling Error
o The Fluctuation of the value of a statistics from
one sample to another drawn from the same population
o The systematic over- representation or under
representation of some segment of the population
in terms of a characteristic relevant to the
research question
44.
45.
46. Specific problem selection.
Systematic documentation of related research.
Effective enumeration.
Effective pre testing.
Controlling methodological bias.
Selection of appropriate sampling techniques.
47.
48.
49. Task- 1
To study the relationship between
Pedometer determined physical activity and
body composition in IT professionals
Quota sampling
50. Task 2
• A study to assess the ut ilization and level of satisfaction of National
Heal th Mission services by the client’s attending community health
centres
• purposive sampling
51. Task 3
• Non-Utilization of antenatal care services among women of
reproductive age in the Niger delta region of Nigeria: Findings from
2595 women
• Multistage sampling
52. Task 4
• Diet Associated Problems and Nutritional Status of Elderly of Selected
Community
• convenience sampling