A sample is a subset of individuals from a larger population. Sampling means selecting the group that you will actually collect data from in your research.

1. PRESENTED BY
MR.KALYAN KUMAR MSC(N)
Sampling techniques

2.  Sampling is process of selecting representative
units from entire population of a study. In research
studies , it is not always possible to study an entire
population therefore the researcher draws a
representative part of population through sampling
process.

3. Types of sampling techniques
Probability sampling
I. Simple random
sampling
II. Stratified random
sampling
III. Systematic random
sampling
IV. Cluster sampling
V. Sequential sampling
Non probability
sampling
I. Purposive sampling
II. Convenient sampling
III. Consecutive sampling
IV. Quota sampling
V. Snow ball sampling

4.  Probability sampling:
It involves random selection of elements. Every
subject in population has equal chance to be selected
as study sample.

5. I. Simple random sampling
 Every population member has a equal chance of
being selected as a subject.
Prerequisites and uses:
 Population should be homogenous
 Must have list of elements/members of accessible
population
 Random selection either by lottery, random table
or computer

6. Advantages
 Most reliable and unbiased method
 Requires minimum knowledge of study population
 Free from sampling errors/bias.
Disadvantages
 Expensive and time consuming.

7. II. Stratified random sampling
 Dividing heterogeneous population in strata based
on selected traits such as age, gender, habitat and
then Random selection of sample from each Strata.
Prerequisites and uses:
 Used for heterogeneous population
Advantages:
 Ensures representative sample in heterogeneous
population
 Comparison is possible in two groups.

8. Disadvantages:
 Requires complete information of population
 Large population is required
 Chances of faulty classification of strata.

9. III. Systematic random sampling
 Selecting of every Kth case from the group ,such as
every 10th person on a patient list or every 100th
person.
Prerequisites and uses
 List of target population must be available
 Random distribution subjects rather than
segregation.

10. Advantages
 Convenient and simple to carry out
 Distribution of sample over entire population.
Disadvantages
 Less representative sample if subjects are non randomly
distributed.

11. IV. Cluster sampling
 When simple random sampling is not possible due to
the size of the population, cluster random sampling
is carried out. Cluster sampling means random
selection of sampling unit consisting of population
elements.
Prerequisites and uses
 When population is a very large
 Random selection of subjects from selected clusters
Advantages
 Cheap,quick and easy for a large population.

12. Disadvantages
 Possibility of high sampling error
 If a small homogenous population is under study,
this technique is not at all useful.

13. V. Sequential sampling
 This method of sample selection is slightly different from
other methods. Here the sample size is not fixed. The
investigator initially selects small sample and tries out to
make inferences; if not able to draw results, he or she
then adds more subjects until clear-cut inferences can be
drawn.

14. Advantages
 Facilitate the references for study on best possible
smallest sample.
Disadvantages
 Not possible to study a phenomenon, which needs to be
studied one point of time.
 Requires the repeated entry into the field to collect the
sample.

15.  Non probability sampling technique wherein
the samples are gathered in a process that does not
give all individuals in the population with equal
chances of being selected in the sample. Elements
are chosen by choice not by a chance.

16. I. Purposive sampling
 Subjects are chosen to be part of the sample with
specific purpose in mind. It is also known as
‘Judgmental’ or ‘Authoritative’ sampling. Samples are
chosen by choice not by chance.
Prerequisites and uses
 Requires in-depth knowledge about the accessible
population
 Used when a limited number of individuals a possess
the trait of interest.

17. Advantages
 Simple to draw a sample
 Saves resources as it requires less field work .
Disadvantages
 Requires considerable knowledge about the population
under study
 It is not always reliable sample.

18. II. Convenience sampling
 Subjects are selected because of their convenient
accessibility and proximity to the researcher.
 The subjects are choose just because of the fact that
there are very easy to recruit for the study. Sometimes, it
is also known as an ‘accidental sampling’.

19. Advantages
 Easiest, cheapest and least time consuming
 Helps in saving time, money and resources.
Disadvantages
 Chances of Sampling bias
 Findings can’t be generalized.

20. III. Consecutive sampling
 It is very similar to convenience sampling, except
that it seeks to include all accessible subjects as a
part of the sample. This non probability sampling
technique can be considered as the best of all non
probability samples because it includes all the
subjects that are available. It is also known as ‘total
enumerative’ sampling.

21. Advantages
 Ensures most representative sample
 Convenient and less time consuming .
Disadvantages
 The researcher has no set plans about sample size
and sampling schedule.

22. IV. Quota sampling
 Equal or proportionate representation of subjects
from each quota. The bases of the quota are usually
age, gender, education, race, religion and social
economic status.

23. Advantages
 Economically cheap economic
 Suitable for studies where fieldwork has to be
carried out.
Disadvantages
 Always does not guarantee representative sample
 Chances of Sampling bias.

24. V. Snowball sampling
 It is used by researchers to identify potential subjects
in studies where subjects are hard to locate. such as
commercial sex workers, drug abusers etc.
 This type of Sampling technique work like chain
referral. Therefore it is also known as ‘chain
referral’ sampling. The researcher asks for
assistance from the subject to identify people with
similar trait of interest after observing the initial
subject .
 Asking subjects to nominate another person with the
same trait.

25. Types of snowball sampling
1. Linear snowball sampling
2. Exponential non discriminative snowball sampling
3. Exponential discriminative snowball sampling.

26. Advantages
 The process is simple , cheap and cost effective
 The sampling technique requires a lesser workforce.
Disadvantages
 Little control of researcher over the sampling
method
 Representativeness of the sample is not guaranteed
 Chances of poor coverage of entire population.

27.  Summary
 Conclusion