2. Population and SamplePopulation and Sample
• PopulationPopulation: A population refers to any: A population refers to any
collection of specified group of humancollection of specified group of human
beings or of non-human entities such asbeings or of non-human entities such as
objects, educational institutions, timeobjects, educational institutions, time
units, geographical areas, prices of wheatunits, 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 RELATEDSOME OTHER RELATED
TERMSTERMS
• Sampling ElementSampling Element : Each entity (person, family,: Each entity (person, family,
group, organization) from the population aboutgroup, organization) from the population about
which information is collected is called awhich 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 thesubject 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 isall units / elements from which the sample is
drawn.drawn.
4. Steps Involved in the process ofSteps Involved in the process of
Sampling:Sampling:
• Defining the populationDefining the population
• Listing the populationListing 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 andPopulation in many cases may be so large and
scattered that a complete coverage may be notscattered that a complete coverage may be not
possible.possible.
• In a short period of time valid and comparableIn a short period of time valid and comparable
results can be obtained.results can be obtained.
• Sampling is economical since it contains fewerSampling is economical since it contains fewer
units.units.
• Research projects sometimes may require theResearch projects sometimes may require the
destruction of the units being tested. So it savesdestruction 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 researcherThe main principle of sampling is that the researcher
seeks knowledge about the population by observing aseeks knowledge about the population by observing a
fewer units and extend the inference about the sample tofewer 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 andSample units must be chosen in a systematic and
objective manner.objective manner.
• Sample units must be clearly defined and easilySample 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 SamplingProbability Sampling
• Non-Probability SamplingNon-Probability Sampling
8. Probability SamplingProbability Sampling
Probability Sampling is one in which everyProbability Sampling is one in which every
unit of a population has a fixed probability ofunit 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 ofEach element must have an equal chance of
being selected.being selected.
• The form of the distribution of the trait in theThe form of the distribution of the trait in the
population can be reasonably be assumed to bepopulation can be reasonably be assumed to be
normal.normal.
9. • Same units of sample should be used throughoutSame units of sample should be used throughout
the study.the study.
• The selection process should be based on someThe selection process should be based on some
sound criteria and should avoid errors, bias andsound 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 homogeneousThis technique is applied in a homogeneous
population. Each unit of the population has anpopulation. 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 samplingStep 2 : Writing numbers listed in the sampling
frame onframe on
small pieces of papers and placing them insmall pieces of papers and placing them in
somesome
vessel.vessel.
– Step 3 : Mixing all papers well and drawing out oneStep 3 : Mixing all papers well and drawing out one
piecepiece
of paper at a time from the vessel.of paper at a time from the vessel.
• Using Random Number tableUsing Random Number table..
12. Stratified Random SamplingStratified Random Sampling
This technique is applied in aThis technique is applied in a
heterogeneous population.heterogeneous population.
• Step I : The population is divided into a numberStep I : The population is divided into a number
of homogeneous strata or sub-groupsof 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 stratumStep 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%)
15. Area or ClusterArea or Cluster
• Step-I : The population is divided into a numberStep-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 clustersStep-II : Instead of drawing a single unit clusters
of units are drawn using simple randomof 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 clustersStep-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 variousIn this method, sampling is done in various
stages, but only the sample of the last units isstages, but only the sample of the last units is
studiedstudied
• Step-I : The population is divided into a number of areasStep-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 (1stst
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(2ndnd
stage).stage).
• Step-V : Sample of units are drawn randomly from theStep-V : Sample of units are drawn randomly from the
selected sub-groups (3selected sub-groups (3rdrd
stage)stage)
17. Multi-phase Random SamplingMulti-phase Random Sampling
The process in this type of sampling isThe 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 isin a Multi-phase sampling, each sample is
adequately studied before another sampleadequately 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 JudgmentalPurposive 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 beingUnits do not have a fixed probability of being
included in the sample. This is usuallyincluded in the sample. This is usually
used when sampling frame is notused when sampling frame is not
available.available.
20. Purposive or Judgmental SamplingPurposive or Judgmental Sampling
The researcher purposively selects those individuals who areThe researcher purposively selects those individuals who are
representative of the population. It is also known as judgmentalrepresentative of the population. It is also known as judgmental
sample because the investigator selects the sample on the basis ofsample 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 investigatorbecause 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 statisticalcan’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 inIt refers to a sampling procedure in
which the investigator selects the personswhich the investigator selects the persons
who are most conveniently available orwho are most conveniently available or
who accidentally come in contact during awho 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 aremeans 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 becauserepresentative of the population because
there is no means of establishingthere is no means of establishing
randomness.randomness.
(ii) In quota sampling, the investigator(ii) In quota sampling, the investigator
selects the most accessible units/ individualsselects 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 orThis sampling is done by selecting or
drawing every nth person from a predetermineddrawing 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 beento 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 elementpersons between every nth element
chosen.chosen.
(ii) In systematic sampling, the(ii) In systematic sampling, the
sampling error increases if the list issampling error increases if the list is
arranged in a particular order, say, the listarranged in a particular order, say, the list
increases or decreases with respect toincreases 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 theSome selected behaviour is usually used as the
basis of contact and/or association in this type ofbasis of contact and/or association in this type of
sampling. Snowball sampling is used for obtaining ansampling. 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 ofnumber of persons are interviewed or a constellation of
friendships converges into some type of a definite socialfriendships converges into some type of a definite social
pattern.pattern.
27. Advantages:Advantages:
(i)(i) Snowball sampling is important andSnowball sampling is important and
helpful in studying small social grouphelpful in studying small social group
and its impact upon formaland its impact upon formal
organizational structure.organizational structure.
(ii)(ii) This method is employed when theThis method is employed when the
target population is unknown or when ittarget population is unknown or when it
is difficult to approach the respondentsis difficult to approach the respondents
in any other way.in any other way.
28. Disadvantages:Disadvantages:
(i)(i) Snowball sampling becomesSnowball sampling becomes
cumbersome and difficult when N iscumbersome and difficult when N is
large.large.
(ii)(ii) The elements included in sample areThe elements included in sample are
dependent on the subjective choices ofdependent on the subjective choices of
the originally selected respondents andthe originally selected respondents and
thereby introduces some bias in thethereby introduces some bias in the
sampling.sampling.
29. Volunteer SamplingVolunteer Sampling
It refers to those sampling in which theIt refers to those sampling in which the
respondent himself/herself volunteers torespondent 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 StudentsAchievement Level of Primary School Students
at the end of Class IV.at the end of Class IV.
• Effects of intervention training on some cognitiveEffects of intervention training on some cognitive
abilities.abilities.
• A study to determine the effects of exposure toA 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 researchThe 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 orPsychological tests are devised to evaluate or
measure behaviour in a standardized way for themeasure behaviour in a standardized way for the
purpose of selection, classification, predictionpurpose of selection, classification, prediction
and guidance as well as for the evaluation ofand guidance as well as for the evaluation of
educational programmes. They are designed toeducational 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 whichTests 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 aCronbach (1964) defines a test as a
systematic procedure for comparing thesystematic procedure for comparing the
behaviour of two or more persons at abehaviour of two or more persons at a
particular time ; or one or more persons atparticular time ; or one or more persons at
different time.different time.
34. Standardized Test:Standardized Test:
A standardized test is one that has specificA standardized test is one that has specific
directions for administration and scoring, adirections for administration and scoring, a
fixed set of test items, and has beenfixed set of test items, and has been
administered to representative samplesadministered to representative samples
taken from the population for whom thetaken from the population for whom the
test is intended for the purpose oftest 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 theOn 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 abilitya) The Tests of General mental ability
or Intelligenceor Intelligence
b) The Tests of Special ability orb) The Tests of Special ability or
AptitudesAptitudes
c) The Tests of Creativityc) The Tests of Creativity
d) The Tests of Attainment ord) 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 madeb) 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 generousA power test is one which has a generous
time limit so that most examinees are abletime 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 timeA speed test is one which has severe time
limit so that no examinees are able tolimit so that no examinees are able to
attempt all items. Speed test measuresattempt all items. Speed test measures
how rapidly or with what speed thehow rapidly or with what speed the
examinees can respond within a givenexaminees 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 Interpretationf) Ease of Interpretation
41. ValidityValidity
Meaning: The term ‘Validity’ meansMeaning: The term ‘Validity’ means
truthfulness or fidelity.truthfulness or fidelity.
Definition:Definition:
• Validity refers to the degree to which a testValidity 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 theThe validity of a test concerns what the
test measures and how well it does sotest measures and how well it does so
(Anastasi, 1988)(Anastasi, 1988)
42. • Validity of a test is defined as the accuracyValidity of a test is defined as the accuracy
with which it measures that which iswith which it measures that which is
intended to measure or as the degree tointended to measure or as the degree to
which it approaches infallibility inwhich it approaches infallibility in
measuring what it purports to measuremeasuring 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 representativenessContent validity is the representativeness
or sampling adequacy of the content – theor sampling adequacy of the content – the
substance, the matter, the topics – of asubstance, the matter, the topics – of a
measuring instrument. It is estimated bymeasuring instrument. It is estimated by
evaluating the relevance of the test items,evaluating the relevance of the test items,
in relation to instructional objectives andin 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 isCriterion related validity is one which is
obtained by comparing (or correlating) theobtained by comparing (or correlating) the
test scores with scores obtained on atest scores with scores obtained on a
criterion available at present or to becriterion 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 isThe degree to which a test is
correlated with a criterion which iscorrelated 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 isThe degree to which a test is
correlated with a criterion which will becorrelated with a criterion which will be
available in the future. It refers to theavailable in the future. It refers to the
association between present results asassociation 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 traitsThe degree to which certain psychological traits
or constructs are actually represented by testor constructs are actually represented by test
performance. Construct validation is an analysisperformance. Construct validation is an analysis
of the meaning of test scores in terms ofof 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 measureExample: If a test is designed to measure
emotional stability, what kinds of evidence areemotional stability, what kinds of evidence are
necessary before we can have confidence thatnecessary before we can have confidence that
the information provided by the test reflects thisthe information provided by the test reflects this
factor ?factor ?
