Sampling techniques

1. SAMPLING TECHNIQUESSAMPLING TECHNIQUES
Mukut HazarikaMukut Hazarika
ProfessorProfessor
Department of EducationDepartment of Education
Dibrugarh UniversityDibrugarh University

2. Population and SamplePopulation and Sample
•PopulationPopulation: A population refers to any : A population refers to any
collection of specified group of human collection of specified group of human
beings or of non-human entities such as beings or of non-human entities such as
objects, educational institutions, time objects, educational institutions, time
units, geographical areas, prices of wheat units, geographical areas, prices of wheat
or salaries drawn by individuals.or salaries drawn by individuals.
•SampleSample: The representative proportion of : The representative proportion of
the population is called a sample.the population is called a sample.

3. SOME OTHER RELATED SOME OTHER RELATED
TERMSTERMS
•Sampling ElementSampling Element : Each entity (person, family, : Each entity (person, family,
group, organization) from the population about group, organization) from the population about
which information is collected is called a which information is collected is called a
sampling element.sampling element.
•Sampling UnitSampling Unit : This is either a single member : This is either a single member
(element) or a collection of members (elements) (element) or a collection of members (elements)
subject to data analysis (and selection) in the subject to data analysis (and selection) in the
sample.sample.
•Sampling FrameSampling Frame : It refers to the complete list of : It refers to the complete list of
all units / elements from which the sample is all units / elements from which the sample is
drawn.drawn.

4. Steps Involved in the process of Steps Involved in the process of
Sampling:Sampling:
•Defining the populationDefining the population
•Listing the population Listing the population
•Selecting a representative sampleSelecting a representative sample
•Obtaining an adequate sampleObtaining an adequate sample

5. Purposes of SamplingPurposes of Sampling
•Population in many cases may be so large and Population in many cases may be so large and
scattered that a complete coverage may be not scattered that a complete coverage may be not
possible.possible.
•In a short period of time valid and comparable In a short period of time valid and comparable
results can be obtained.results can be obtained.
•Sampling is economical since it contains fewer Sampling is economical since it contains fewer
units.units.
•Research projects sometimes may require the Research projects sometimes may require the
destruction of the units being tested. So it saves destruction of the units being tested. So it saves
destruction of units.destruction of units.

6. Principles of SamplingPrinciples of Sampling
The main principle of sampling is that the researcher The main principle of sampling is that the researcher
seeks knowledge about the population by observing a seeks knowledge about the population by observing a
fewer units and extend the inference about the sample to fewer units and extend the inference about the sample to
the entire population. the entire population.
The principles of sampling are :The principles of sampling are :
•Sample units must be chosen in a systematic and Sample units must be chosen in a systematic and
objective manner.objective manner.
•Sample units must be clearly defined and easily Sample units must be clearly defined and easily
identifiable.identifiable.
•Sample units must be independent of each other.Sample units must be independent of each other.

7. Types of SamplingTypes of Sampling
•Probability Sampling Probability Sampling
•Non-Probability SamplingNon-Probability Sampling

8. Probability SamplingProbability Sampling
Probability Sampling is one in which every Probability Sampling is one in which every
unit of a population has a fixed probability of unit of a population has a fixed probability of
being included in the samplebeing included in the sample..
Conditions to be satisfied for Probability sampling :Conditions to be satisfied for Probability sampling :
•Complete list of units to be studied is available.Complete list of units to be studied is available.
•Size of the population must be known.Size of the population must be known.
•Each element must have an equal chance of Each element must have an equal chance of
being selected.being selected.
•The form of the distribution of the trait in the The form of the distribution of the trait in the
population can be reasonably be assumed to be population can be reasonably be assumed to be
normal.normal.

9. •Same units of sample should be used throughout Same units of sample should be used throughout
the study.the study.
•The selection process should be based on some The selection process should be based on some
sound criteria and should avoid errors, bias and sound criteria and should avoid errors, bias and
distortions.distortions.

10. Types of Probability SamplingTypes of Probability Sampling
•Simple or Unrestricted Random samplingSimple or Unrestricted Random sampling
•Stratified Random SamplingStratified Random Sampling
•Area or Cluster SamplingArea or Cluster Sampling
•Multi-stage SamplingMulti-stage Sampling
•Multi-phase SamplingMulti-phase Sampling

11. Simple or Unrestricted Random SamplingSimple or Unrestricted Random Sampling
This technique is applied in a homogeneous This technique is applied in a homogeneous
population. Each unit of the population has an population. Each unit of the population has an
equal chance of being selected for the sample.equal chance of being selected for the sample.
Methods Adopted :Methods Adopted :
•LotteryLottery : :
–Step 1 : Constructing the Sampling FrameStep 1 : Constructing the Sampling Frame
–Step 2 : Writing numbers listed in the sampling Step 2 : Writing numbers listed in the sampling
frame on frame on
small pieces of papers and placing them in small pieces of papers and placing them in
some some
vessel.vessel.
–Step 3 : Mixing all papers well and drawing out one Step 3 : Mixing all papers well and drawing out one
piece piece
of paper at a time from the vessel.of paper at a time from the vessel.
•Using Random Number tableUsing Random Number table..
•Using Electronic DevicesUsing Electronic Devices..

12. Stratified Random SamplingStratified Random Sampling
This technique is applied in a This technique is applied in a
heterogeneous population.heterogeneous population.
•Step I : The population is divided into a number Step I : The population is divided into a number
of homogeneous strata or sub-groups of homogeneous strata or sub-groups
based on one or more criteria.based on one or more criteria.
•Step II : A sample is drawn from each stratum Step II : A sample is drawn from each stratum
using simple random technique.using simple random technique.
Types of Stratified Random Sampling :Types of Stratified Random Sampling :
–Proportionate Stratified Random SamplingProportionate Stratified Random Sampling
–Dis-proportionate Sratified Random SamplingDis-proportionate Sratified Random Sampling

13. Proportionate Stratified SamplingProportionate Stratified Sampling
Class X
Students
(1000)
Urban
(400)
Rural
(600)
Boys
(250)
Girls
(150)
Boys
(400)
Girls
(200)
25( 10%)
15(10%)40(10%) 20(10%)

14. Disproportionate Stratified SamplingDisproportionate Stratified Sampling
Class X
Students
(1000)
Urban
(400)
Rural
(600)
Boys
(250)
Girls
(150)
Boys
(400)
Girls
(200)
50( 20%)
50(33.3%) 50(12.5%) 50(25%)

15. Area or ClusterArea or Cluster
•Step-I : The population is divided into a number Step-I : The population is divided into a number
of clusters each having a number of units.of clusters each having a number of units.
•Step-II : Instead of drawing a single unit clusters Step-II : Instead of drawing a single unit clusters
of units are drawn using simple random of units are drawn using simple random
technique.technique.
•Step-III : Usually clusters are drawn in multi-Step-III : Usually clusters are drawn in multi-
stages.stages.
•Step-IV : Usually all the units of the clusters Step-IV : Usually all the units of the clusters
drawn are used as the sample.drawn are used as the sample.

16. Multi-stage Random SamplingMulti-stage Random Sampling
In this method, sampling is done in various In this method, sampling is done in various
stages, but only the sample of the last units is stages, but only the sample of the last units is
studiedstudied
•Step-I : The population is divided into a number of areas Step-I : The population is divided into a number of areas
or clusters.or clusters.
•Step-II : A sample of clusters is drawn (1Step-II : A sample of clusters is drawn (1
stst
Stage) Stage)
•Step-III : Each selected cluster is divided into more sub-Step-III : Each selected cluster is divided into more sub-
groups ( clusters).groups ( clusters).
•Step-IV : A sample of sub-groups is drawn randomlyStep-IV : A sample of sub-groups is drawn randomly
(2(2
ndnd
stage). stage).
•Step-V : Sample of units are drawn randomly from the Step-V : Sample of units are drawn randomly from the
selected sub-groups (3selected sub-groups (3
rdrd
stage) stage)

17. Multi-phase Random SamplingMulti-phase Random Sampling
The process in this type of sampling is The process in this type of sampling is
same as in Multi-stage sampling; however, same as in Multi-stage sampling; however,
in a Multi-phase sampling, each sample is in a Multi-phase sampling, each sample is
adequately studied before another sample adequately studied before another sample
is drawn from it.is drawn from it.

18. Types of Non-probability SamplingTypes of Non-probability Sampling
•Purposive Sampling or Judgmental Purposive Sampling or Judgmental
SamplingSampling
•Accidental/Incidental SamplingAccidental/Incidental Sampling
•Volunteer SamplingVolunteer Sampling
•Quota SamplingQuota Sampling
•Systematic SamplingSystematic Sampling
•Snow Ball SamplingSnow Ball Sampling

19. Non-Probability SamplingNon-Probability Sampling
Units do not have a fixed probability of being Units do not have a fixed probability of being
included in the sample. This is usually included in the sample. This is usually
used when sampling frame is not used when sampling frame is not
available.available.

20. Purposive or Judgmental SamplingPurposive or Judgmental Sampling
The researcher purposively selects those individuals who are The researcher purposively selects those individuals who are
representative of the population. It is also known as judgmental representative of the population. It is also known as judgmental
sample because the investigator selects the sample on the basis of sample because the investigator selects the sample on the basis of
his/her own judgment.his/her own judgment.
Advantages:Advantages:
(i) It is less costly and more readily accessible to the (i) It is less costly and more readily accessible to the
researcher.researcher.
(ii) Purposive sampling guarantees that those individuals will be (ii) Purposive sampling guarantees that those individuals will be
included in the sample that are representative of the population.included in the sample that are representative of the population.
Disadvantages:Disadvantages:
(i) Purposive sampling introduces subjectivity in the sampling (i) Purposive sampling introduces subjectivity in the sampling
because too much emphasis is given on the ability of the investigator because too much emphasis is given on the ability of the investigator
to assess which element is typical of the population.to assess which element is typical of the population.
(ii) In the case of purposive sampling the inferential statistics (ii) In the case of purposive sampling the inferential statistics
can’t be used legitimately, because, under all inferential statistical can’t be used legitimately, because, under all inferential statistical
techniques, there is an assumption of randomness.techniques, there is an assumption of randomness.

21. Accidental / Incidental SamplingAccidental / Incidental Sampling
It refers to a sampling procedure in It refers to a sampling procedure in
which the investigator selects the persons which the investigator selects the persons
who are most conveniently available or who are most conveniently available or
who accidentally come in contact during a who accidentally come in contact during a
certain period of time in the research. certain period of time in the research.

22. Quota SamplingQuota Sampling
Steps followedSteps followed::
(i) The population is divided into different (i) The population is divided into different
strata.strata.
(ii) From each stratum a quota is selected.(ii) From each stratum a quota is selected.
Advantages:Advantages:
(i) Quota samples are the most satisfactory (i) Quota samples are the most satisfactory
means when quick and crude results are means when quick and crude results are
desired.desired.
(ii) It can guarantee the inclusion of (ii) It can guarantee the inclusion of
individuals from different strata of population.individuals from different strata of population.
(iii) It is less costly. (iii) It is less costly.

23. Disadvantages:Disadvantages:
(i) The selected sample is not (i) The selected sample is not
representative of the population because representative of the population because
there is no means of establishing there is no means of establishing
randomness.randomness.
(ii) In quota sampling, the investigator (ii) In quota sampling, the investigator
selects the most accessible units/ individuals selects the most accessible units/ individuals
which may not be typical of the population.which may not be typical of the population.

24. Systematic SamplingSystematic Sampling
This sampling is done by selecting or This sampling is done by selecting or
drawing every nth person from a predetermined drawing every nth person from a predetermined
list of elements or individuals.list of elements or individuals.
Advantages:Advantages:
(i) Systematic sampling is relatively a quick (i) Systematic sampling is relatively a quick
method of obtaining a sample of elements.method of obtaining a sample of elements.
(ii) Systematic sampling makes it very easy (ii) Systematic sampling makes it very easy
to check whether every nth person has been to check whether every nth person has been
selected.selected.

25. Disadvantages:Disadvantages:
(i) Systematic sampling ignores all (i) Systematic sampling ignores all
persons between every nth element persons between every nth element
chosen.chosen.
(ii) In systematic sampling, the (ii) In systematic sampling, the
sampling error increases if the list is sampling error increases if the list is
arranged in a particular order, say, the list arranged in a particular order, say, the list
increases or decreases with respect to increases or decreases with respect to
some trait such as age, education, some trait such as age, education,
income, caste, etc.income, caste, etc.

26. Snowball SamplingSnowball Sampling
Some selected behaviour is usually used as the Some selected behaviour is usually used as the
basis of contact and/or association in this type of basis of contact and/or association in this type of
sampling. Snowball sampling is used for obtaining an sampling. Snowball sampling is used for obtaining an
impression of informal social relations among individuals.impression of informal social relations among individuals.
Steps followed:Steps followed:
(i) At first few respondents are selected who (i) At first few respondents are selected who
are known and available to the researcher.are known and available to the researcher.
(ii) These respondents give other names who (ii) These respondents give other names who
meet the criteria of research.meet the criteria of research.
(iii) This process is continued until adequate (iii) This process is continued until adequate
number of persons are interviewed or a constellation of number of persons are interviewed or a constellation of
friendships converges into some type of a definite social friendships converges into some type of a definite social
pattern.pattern.

27. Advantages:Advantages:
(i)(i)Snowball sampling is important and Snowball sampling is important and
helpful in studying small social group helpful in studying small social group
and its impact upon formal and its impact upon formal
organizational structure.organizational structure.
(ii)(ii) This method is employed when the This method is employed when the
target population is unknown or when it target population is unknown or when it
is difficult to approach the respondents is difficult to approach the respondents
in any other way.in any other way.

28. Disadvantages:Disadvantages:
(i)(i)Snowball sampling becomes Snowball sampling becomes
cumbersome and difficult when N is cumbersome and difficult when N is
large.large.
(ii)(ii)The elements included in sample are The elements included in sample are
dependent on the subjective choices of dependent on the subjective choices of
the originally selected respondents and the originally selected respondents and
thereby introduces some bias in the thereby introduces some bias in the
sampling.sampling.

29. Volunteer SamplingVolunteer Sampling
It refers to those sampling in which the It refers to those sampling in which the
respondent himself/herself volunteers to respondent himself/herself volunteers to
give information.give information.

30. SOME RESEARCH PROBLEMS:SOME RESEARCH PROBLEMS:
•Mathematical creativity and some socio-Mathematical creativity and some socio-
psychological factors of Hindus and Muslims.psychological factors of Hindus and Muslims.
•Construction and Standardization of a Multiple-Construction and Standardization of a Multiple-
choice Reading Comprehension test.choice Reading Comprehension test.
•Achievement Level of Primary School Students Achievement Level of Primary School Students
at the end of Class IV.at the end of Class IV.
•Effects of intervention training on some cognitive Effects of intervention training on some cognitive
abilities.abilities.
•A study to determine the effects of exposure to A study to determine the effects of exposure to
pre-school education on cognitive abilities.pre-school education on cognitive abilities.

31. Data-Gathering ToolsData-Gathering Tools
The major data-gathering tools of research The major data-gathering tools of research
are:are:
•Psychological TestsPsychological Tests
•Inquiry FormsInquiry Forms
•ObservationObservation
•InterviewInterview
•Sociometric TechniqueSociometric Technique

32. Psychological TestsPsychological Tests
Psychological tests are devised to evaluate or Psychological tests are devised to evaluate or
measure behaviour in a standardized way for the measure behaviour in a standardized way for the
purpose of selection, classification, prediction purpose of selection, classification, prediction
and guidance as well as for the evaluation of and guidance as well as for the evaluation of
educational programmes. They are designed to educational programmes. They are designed to
measure general mental ability or intelligence, measure general mental ability or intelligence,
special abilities or aptitudes, creativity, special abilities or aptitudes, creativity,
achievement, personality traits and adjustment, achievement, personality traits and adjustment,
interests and values.interests and values.

33. What are tests ?What are tests ?
•Tests consist of a series of tasks which Tests consist of a series of tasks which
the subject is required to perform.the subject is required to perform.
•Cronbach (1964) defines a test as a Cronbach (1964) defines a test as a
systematic procedure for comparing the systematic procedure for comparing the
behaviour of two or more persons at a behaviour of two or more persons at a
particular time ; or one or more persons at particular time ; or one or more persons at
different time.different time.

34. Standardized Test:Standardized Test:
A standardized test is one that has specific A standardized test is one that has specific
directions for administration and scoring, a directions for administration and scoring, a
fixed set of test items, and has been fixed set of test items, and has been
administered to representative samples administered to representative samples
taken from the population for whom the taken from the population for whom the
test is intended for the purpose of test is intended for the purpose of
establishing norms (Koul, 1997). establishing norms (Koul, 1997).

35. Classification of TestsClassification of Tests
•On the basis of Time limit in producing the On the basis of Time limit in producing the
response:response:
a) Power Testa) Power Test
b) Speed Testb) Speed Test
•On the basis of Administrative conditions:On the basis of Administrative conditions:
a) Group testa) Group test
b) Individual testb) Individual test

36. •On the basis of Purposes:On the basis of Purposes:
a) The Tests of General mental ability a) The Tests of General mental ability
or Intelligenceor Intelligence
b) The Tests of Special ability or b) The Tests of Special ability or
AptitudesAptitudes
c) The Tests of Creativityc) The Tests of Creativity
d) The Tests of Attainment or d) The Tests of Attainment or
AchievementAchievement
e) The Personality measurese) The Personality measures

37. •On the basis of Standardization:On the basis of Standardization:
a) Standardized Testsa) Standardized Tests
b) Non-Standardized Teacher made b) Non-Standardized Teacher made
teststests
•On the basis of Nature of Items:On the basis of Nature of Items:
a) Verbal Testa) Verbal Test
b) Nonverbal Testb) Nonverbal Test
c) Performance testc) Performance test

38. •On the basis of Scoring:On the basis of Scoring:
a) Objective Type Testa) Objective Type Test
b) Essay Type Testb) Essay Type Test

39. •Power Test:Power Test:
A power test is one which has a generous A power test is one which has a generous
time limit so that most examinees are able time limit so that most examinees are able
to attempt every item.to attempt every item.
•Speed Test:Speed Test:
A speed test is one which has severe time A speed test is one which has severe time
limit so that no examinees are able to limit so that no examinees are able to
attempt all items. Speed test measures attempt all items. Speed test measures
how rapidly or with what speed the how rapidly or with what speed the
examinees can respond within a given examinees can respond within a given
time limit.time limit.

40. Characteristics of TestsCharacteristics of Tests
•ValidityValidity
•ReliabilityReliability
•UsabilityUsability
a) Objectivitya) Objectivity
b) Economy of Timeb) Economy of Time
c) Costc) Cost
d) Ease of Administrationd) Ease of Administration
e) Ease of Scoringe) Ease of Scoring
f) Ease of Interpretation f) Ease of Interpretation

41. ValidityValidity
Meaning: The term ‘Validity’ means Meaning: The term ‘Validity’ means
truthfulness or fidelity.truthfulness or fidelity.
Definition:Definition:
•Validity refers to the degree to which a test Validity refers to the degree to which a test
measures what it claims to measure.measures what it claims to measure.
•The validity of a test concerns what the The validity of a test concerns what the
test measures and how well it does so test measures and how well it does so
(Anastasi, 1988)(Anastasi, 1988)

42. •Validity of a test is defined as the accuracy Validity of a test is defined as the accuracy
with which it measures that which is with which it measures that which is
intended to measure or as the degree to intended to measure or as the degree to
which it approaches infallibility in which it approaches infallibility in
measuring what it purports to measure measuring what it purports to measure
(Lindquist, 1951)(Lindquist, 1951)

43. Types of Validity:Types of Validity:
•Content ValidityContent Validity
•Criterion-Related ValidityCriterion-Related Validity
a) Concurrent Validitya) Concurrent Validity
b) Predictive Validityb) Predictive Validity
•Construct ValidityConstruct Validity

44. Content validity:Content validity:
Content validity is the representativeness Content validity is the representativeness
or sampling adequacy of the content – the or sampling adequacy of the content – the
substance, the matter, the topics – of a substance, the matter, the topics – of a
measuring instrument. It is estimated by measuring instrument. It is estimated by
evaluating the relevance of the test items, evaluating the relevance of the test items,
in relation to instructional objectives and in relation to instructional objectives and
actual subject matter studied.actual subject matter studied.

45. Criterion-Related Validity:Criterion-Related Validity:
Criterion related validity is one which is Criterion related validity is one which is
obtained by comparing (or correlating) the obtained by comparing (or correlating) the
test scores with scores obtained on a test scores with scores obtained on a
criterion available at present or to be criterion available at present or to be
available in the future.available in the future.
a) Concurrent Validitya) Concurrent Validity::
The degree to which a test is The degree to which a test is
correlated with a criterion which is correlated with a criterion which is
available at the present time.available at the present time.

46. b) Predictive Validity:b) Predictive Validity:
The degree to which a test is The degree to which a test is
correlated with a criterion which will be correlated with a criterion which will be
available in the future. It refers to the available in the future. It refers to the
association between present results as association between present results as
indicated by a test and future behaviour.indicated by a test and future behaviour.

47. Construct ValidityConstruct Validity::
The degree to which certain psychological traits The degree to which certain psychological traits
or constructs are actually represented by test or constructs are actually represented by test
performance. Construct validation is an analysis performance. Construct validation is an analysis
of the meaning of test scores in terms of of the meaning of test scores in terms of
psychological constructs (Cronbach and Meehl , psychological constructs (Cronbach and Meehl ,
1955).1955).
Example: If a test is designed to measure Example: If a test is designed to measure
emotional stability, what kinds of evidence are emotional stability, what kinds of evidence are
necessary before we can have confidence that necessary before we can have confidence that
the information provided by the test reflects this the information provided by the test reflects this
factor ?factor ?