population and sampling in nursing research

population and sampling in nursing research

1. College of Education
School of Continuing and Distance Education
2014/2015 –2016/2017
NURS 345
NURSING RESEARCH
Session 9 –POPULATION AND SAMPLING
Lecturer: Dr. Florence Naab, University of Ghana School of Nursing
Contact Information: [email protected]

2. Session Overview
•The availability of a population and a sample are important
determinants of the feasibility of any research. This session
will discuss population, sample, and sampling techniques. By
the end of the session, the student will be able to:
1.Differentiate between population and sample.
2.Describe various sampling techniques.
Slide 2

3. Session Outline
The key topics to be covered in the session are as follows:
Topic one: Population and sample
Topic two: Sampling techniques
Slide 3

4. Reading List
Chapter 11 of;
Nieswiadomy, R.M (2008). Foundations of Nursing Research.
5th Ed. Pearson Education, USA.
Slide 4

5. POPULATION AND SAMPLE
Topic One
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6. What is a research population?
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7. Population
Refers to all cases but not limited to only people e.gall
University of Ghana students or all public universities in
Ghana.
It may be impossible to deal with whole populations in
research.
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8. Sample
A sample is a selection
from the population.
Involves decisions about
who/what should be
studied.
There must be a well
defined plan for sampling.
The sample size is the
total number of people or
cases included in a
research.
Selected sample
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9. Differences between population and
sample
Slide 9

10. SAMPLING TECHNIQUE
Topic Two
Slide 10

11. Sampling techniques
There are two main categories of sampling
techniques:
1.Probability sampling: Here the technique used to
select each respondent is known e.gevery 10
th
persons
of level 300 nursing students whose surnames start
with a ‘B’.
2.Non-probability sampling: the technique used to
select each respondent is not known.
1.These are less complicated and used when there is no
need to make any statistical generalization to any
population beyond the sample used.
Slide 11

12. Probability sampling techniques
These techniques give each participant an equal chance
of being selected:
Simple random sampling
Systematic sampling
Stratified random sampling
Cluster sampling
Multistage sampling
Note: Each technique will be elaborated in subsequent
slides.
Slide 12

13. Simple random sampling
Each participant is
chosen at random
List of the whole
population is needed to
produce a simple
random sample. This
gives every individual in
the population an equal
chance of being
selected.
Chosen at random
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14. Systematic sampling
Involves choosing a starting point in the sampling
frame at random, and then choosing every nth
individual e.gall even numbers in the sampling frame
or every 10
th
person in the sampling frame.
The starting point should also be selected at random,
e.gwhether even numbers or every 10
th
person
should be a random selection.
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15. What is stratified random sampling?
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16. Stratified random sampling
Involves dividing the population into groups or strata,
members of the group must have similar
characteristics e.g
level 300 female nursing students –group A
Leve300 male nursing students –group B
There is then random sampling within each group.
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17. Cluster sampling
Involves dividing the population into a number of
units or clusters with a range of characteristics
The clusters themselves are chosen on a random
basis.
Then random sampling within each group is done.
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18. Multistage sampling
Is an extension of cluster sampling.
Involves selecting the sample in stages, basically
taking samples from samples.
Also involves stratification of the sample.
Slide 18

19. Non-probability sampling techniques
Purposive sampling
Quota sampling
Dimensional sampling
Convenience sampling
Snowball sampling
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20. Purposive sampling
The principle of selection is based on the
researcher’s judgment to achieve a particular
interest or purpose.
A sample is built up that allows the researcher to
satisfy specific needs in the research.
Slide 20

21. Quota sampling
This technique obtains representatives of various
elements of a population e.ga quota each from
levels 100, 200, 300, and 400 nursing students.
Then a convenience sampling is used within each
category.
A quota of each category will be interviewed, e.gby
convenience, 5 students will be interviewed within
each level of nursing students.
Slide 21

22. Dimensional sampling
Is an extension of quota sampling in which various
important dimensions are represented, e.g2 females
and 2 males (aged between 18 to 25 years) of levels
100, 200, 300, and 400 nursing students will be
sampled by convenience.
In the above example, age is the dimension within
each level.
Slide 22

23. Convenience sampling
Involves choosing the most convenient and available
people as participants.
The process is continued until the required sample
size is achieved.
It is the most widely used but less satisfactory in
research because it lacks representativeness of the
population.
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24. Snowball sampling
Only one or more individuals are identified by the
researcher from the population of interest.
The identified participants are used as informants to
identify other members of the population, after they
have been interviewed.
Snowball sampling is useful when it is difficult to
identify members of a population of interest.
Slide 24

25. Summary and conclusion
This session has discussed research population,
sample, and various sampling techniques used in
nursing research.
The next session will discuss data collection methods
Slide 25

26. References
Creswell, J. W. (2003). Research Design: Qualitative,
quantitative, Mixed Methods Approaches.2
nd
Ed. Sage
Publications
Nieswiadomy, R.M (2008). Foundations of Nursing Research.
5th Ed. Pearson Education, USA.
Polit, D. F. and Beck, C.T (2008). Nursing Research: Generating
and Assessing Evidence for Nursing Practice. 8th Ed.
Lippincott Williams & Wilkins, USA.
Robsin, C. (2002). Real World Research: A Resource for Social
Scientist and Practitioner-Researchers. 2nd Ed. ISBN,
USA.
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