Sampling Technique

2. By:By:
Community Medicine Deptt:Community Medicine Deptt: BILAWAL MEDICAL COLLEGEBILAWAL MEDICAL COLLEGE
(LUMHS)(LUMHS) Jamshoro, Sind,Jamshoro, Sind, PakistanPakistan
e maile mail mnajeeb80@gmail.commnajeeb80@gmail.com
LIAQUAT
MEDICAL
UNIVERSITY

7. POPULATIONPOPULATION
 The whole group of the individuals
on which the results of the study are
to be generalized is known as
Population. A
SAMPLE
 small group of individuals chosen for the
study is known as Sample.
The entire group of people of interest from whom
the researcher needs to obtain information.
The selection of a subset of the population

8. A Population of 100A Population of 100

9. Sampling FrameSampling Frame
 Listing of all the members of the universe
from which the sample is to be taken , is
known as Sampling Frame.
 Sampling frame should be carefully
developed as it affects the results drawn.
Listing of population from which a sample is chosen

10. WHY SAMPLING ISWHY SAMPLING IS
NECESSARY?NECESSARY?
 Convenient.
 Economic.
 Time saving.
 Less resources are required.
 Easy to interpret the data.

11. TYPES OF SAMPLINGTYPES OF SAMPLING
• A. Probability Sampling MethodsProbability Sampling Methods
• (All having equal chance)(All having equal chance)
• B. Non Probability Sampling MethodsB. Non Probability Sampling Methods
• (Not all having equal chance)(Not all having equal chance)

12. 14-12
SAMPLES TECHNIQUESSAMPLES TECHNIQUES
A.A. Probability Sampling MethodsProbability Sampling Methods
Simple RandomSimple RandomSimple RandomSimple Random
systemic samplingsystemic samplingsystemic samplingsystemic sampling
StratifiedStratifiedStratifiedStratified
ClusterClusterClusterCluster
MultistageMultistageMultistageMultistage

13. 14-13
B. Non probabilityB. Non probability
Sampling MethodsSampling Methods
ConvenienceConvenienceConvenienceConvenience
JudgmentJudgmentJudgmentJudgment
QuotaQuotaQuotaQuota
SnowballSnowballSnowballSnowball

14.  Each element in the population will have
an equal chance of being included in the
sample.
1 - 14
1. Simple Random sampling1. Simple Random sampling1. Simple Random sampling1. Simple Random sampling
No: is given to each of units (Persons/ houses)
Table of random Nos: is used
Samples selected haphazardly
(Each has equal chance of being selected)
N = 100 population size, n = 8 sample size
OR Lottery Method
E.g:- In Electro roll / Census

15. Simple random sampling

16. A Simple Random SampleA Simple Random Sample

17.  Selecting unit/ personSelecting unit/ person after a regularafter a regular
intervalinterval
1 - 17
2.2. systemic samplingsystemic sampling2.2. systemic samplingsystemic sampling

18. Systematic sampling

19. 3. Stratified3. Stratified3. Stratified3. Stratified
It involves division of
population in to smaller
groups (homogenous subgroups)
known as “Strata”
•Then Simple random
sampling OR systematic
sampling is applied with
each stratum.
Example 2 Population is
divided on the basis of
characteristic of interest in the
population E.g. male & female
may have different
consumption patterns.

20. 1 - 20

21. A Stratified, Systematic SampleA Stratified, Systematic Sample
with a Random Startwith a Random Start

22.  Here we select a simple random sample of
groups such as a certain number of city
blocks & then select a person each from
each block.
 This technique is more economical than the random selection of
persons through out the city.
4. Cluster4. Cluster4. Cluster4. Cluster

23. Cluster samplingCluster sampling
Section 4
Section 5
Section 3
Section 2Section 1

24. • Sampling at different stages/ Levels
• 1. National level
• 2. Provincial level
• 3. District level
5. Multistage5. Multistage5. Multistage5. Multistage
 A sample selected in stages, beginning with the most
unspecific level (such as regions) and ending with the
most specific (such as houses on selected city blocks).

25. Non probability MethodsNon probability Methods

26. NON PROBABILITYNON PROBABILITY
SAMPLINGSAMPLING
• Convenient
• Economic
BUT
RESULTS CAN NOT BE GENERALIZED
THEREFORE
Some probability factor is needed to be
imposed to ensure a degree of
representation in the sample.

27.  A convenience sample is a sample where the
patients are selected, in part or in whole,
at the convenience of the researcher.
Example:
 Male on street interviews
 Teacher uses students
1. Convenience /Accidental/Incidental sampling1. Convenience /Accidental/Incidental sampling1. Convenience /Accidental/Incidental sampling1. Convenience /Accidental/Incidental sampling
 Involves the use of the most convenient &
readily available subjects for sample.
A convenience sample is made up of people who are easy to reach

29.  The researcher chooses the sample based on
who they think would be appropriate for the study.
2. Judgment /Purposive2. Judgment /Purposive2. Judgment /Purposive2. Judgment /Purposive

31. 3. Quota3. Quota3. Quota3. Quota
if you are a researcher conducting a national quota sample, you
might need to know what proportion of the population is
male(40) and what proportion is female (60) as well as what
proportions of each gender fall into different age categories, race
or ethnic categories, educational categories, etc.
Researcher selects people according to some fixed quota.
Male 40
Female 60
Total (Fixed quota) 100

32. Researcher collects data on the few members of the
target population he or she can locate,
then asks those individuals to provide information
needed to locate other members of that population
whom they know.
4. Snowball4. Snowball4. Snowball4. Snowball
Get sampled people to nominate others

34. Sampling ErrorsSampling Errors
A. Size: sample size should be large as possible
depends upon feasibility (time, person, importance of data)
B. subject variation: Sometimes observation may be changed on
different times (B.P at different times of a day)
C. Observer Variation: When 2 or more persons observe same data
(No same value) E.g:- Taking Blood Pressure reading
D. Technical Fault: By Instrument
E. Incomplete Coverage: If 10 out of 100 are non cooperative (i,e 90
or 10 Non co operative)

35. THANKYOU