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7/28/2019 2 Introduction to Sampling and Survey Design
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Applied Marketing
(Market Research Methods)
Topic 2:
Introduction to samplingand survey design
Dr James Abdey
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Overview
Aim:
To establish a common language and understandingof setting up a commercial market research / samplesurvey
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stages of market research
1. Research brief
2. Research proposal
3. Data collection
4. Data analysis and evaluation
5. Preparation and presentation of research report
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stage 1: Research brief
Define the marketing problem
Exploratory research
Consultation
Informal discussions
Developing survey objectives
Target population
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stage 2: Research proposal
Nature of the problem
Population involved
Methodology to be adopted
Estimate time and costs
Example: New packaging of a product
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stage 3: Data collection
Survey design (sampling scheme) Questionnaire design
Mode of data collection
Sample size
Sources of error Sampling error Measurement errors
Aim: To produce meaningful numbers relating to the
population studied
Bad data will produce bad and useless results!
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stage 4: Data analysis and
evaluation
Descriptive statistics (means, proportions, variances,
ratios, etc.)
Plots and graphs
Cross-tabulations
Statistical modelling (regression analysis)
Multivariate analysis
Time series analysis
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Stage 5: Presentation of results
Tables
Graphs
Report
Output from statistical analysis should be clearly and
appropriately discussed
Results discussed must answer the main research
questions set in Stage 1
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Glossary
Population: Group of people or objects that we
would like to study in a particular survey
Target population
Survey population
Census: Total enumeration / study of the population
Sample: A number of sampling units selected from a
population and studied
Elementary sampling unit: The element being
sampled from a population (individuals, supermarket,
hospitals, etc.)
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Sample surveys
Surveys involve collecting new data about a
population
They are based on samples rather than censuses
Surveys are conducted in the real world under
circumstances that cannot be fully controlled
The procedures of sampling are explicit,
systematic and standardised
The sample sizes can be large
They require much planning and teamwork
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Examples of sample surveys
Demography: study of births, deaths, family
formation, etc.
Social psychology: study of perceptions, attitudes,
individual and group behaviour
Political science: study of voting
Market research: study of customer perceptions,
choice of products and services, use of services, etc.
Government: employment, education, health,
income, housing, crime, etc.
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Introduction tosampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Something to think about
The manager of a multiplex cinema is anxious to
know how it is perceived, i.e. the image people have
of the cinema
Identify three possible populations that may be
surveyed to obtain this information
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Definitions
The aim of sampling is to select a representative
sample from a population
It is important to understand the mechanisms,
limitations and advantages of sampling
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Survey objective 1: Fairness
It would be difficult to justify a method that was
biased
For this reason sampling survey methodology places
a great emphasis on unbiased surveys and
unbiased estimators
Bias can arise from
Sample selection The use of the wrong sampling frame Non-response Other
I d i
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Selection bias
Selection bias is avoided with the use of random, or
probability, sample designs
The basic method of simple random sampling
(SRS) is used to justify fairness
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Introduction toS bj i 3 C
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Survey objective 3: Cost
A widely used method for reducing cost is cluster
sampling
Once again this uses SRS to ensure fairness but the
survey is conducted in such a way to reduce
sampling costs due to travel and time
Introduction toS li f
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Sampling frame
A sampling frame is a list of all population elements(for example, register of electors, postcode
addresses, etc.)
Issues to consider
Adequacy Completeness (missing units) No duplication Accuracy (dynamic populations) Convenience (accessibility)
Introduction toS f ti l li f
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Sources of national sampling frames
in UK
Registor of electors
Compiled in October, published in February 7% of eligible voters are not on the register Names in alphabetical order, not by address No age information
Postcode Address File (PAF)
Used in Family Expenditure Survey General Household Survey Labour Force Survey National Food Survey
Introduction toPostcode Address File (PAF)
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Postcode Address File (PAF)
Postcode Address File (PAF)
UK
120 Areas
2700 Districts
8900 Sectors
1.5 million post codes
(22 million addresses)
1.3 million small users1700000 large users
Introduction toSomething for you to think about
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Introduction tosampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Something for you to think about
The chamber of commerce in a large town wishes to
conduct a random sample of retail outlets in the town
It is proposing to use a local commercial directory as
a sampling frame
To what extent could this sampling frame lead to
bias?
How might such bias be minimised?
Introduction toStatistic/estimator and parameter
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sampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Statistic/estimator and parameter
Statistic or estimator: any quantity calculated from
a sample to estimate a population parameter (for
example, sample mean, sample variance, sample
proportion, sample percentage)
Parameter: The value of an attribute calculated in
the population (for example, population mean,
population variance, population proportion,
population percentage)
Introduction toSampling variability and error
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sampling andsurvey design
Dr James Abdey
OverviewStages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Sampling variability and error
Different samples drawn from a fixed population have
different statistics
In contrast, population parameters are fixed
(constant)
Hence we typically experience sampling variability
Sampling error refers to the difference between a
sample estimate (such as the sample mean, x) and
the value of the population parameter (such as thepopulation mean, )
x
Introduction toSampling distribution of a sample
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Sampling distribution of a sample
statistic
Estimator bias is the difference between the mean
(expected) value of the sampling distribution and the
true parameter value
E(X)
Sample variance is the spread of the sampling
distribution, denoted
Variance(X) = Var(X)
Introduction toli dStatistics and parameters
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Statistics and parameters
Sample statistics (calculated using sample data)
Sample mean: X Sample variance: S2
Sample standard deviation: S
Population parameters (to be estimated using
sample statistics)
Population mean: Population variance: 2
Population standard deviation:
Introduction toli dDesirable properties for the
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Desirable properties for the
estimators
Unbiasedness for example, E(X) =
Efficiency small standard errors
Consistency sample statistic approaches the
population parameter that is to be estimated as the
sample size increases
Introduction tosampling andProbability (or random) sampling
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Probability (or random) sampling
In population (or random) sampling, every
population element has a known, non-zeroprobability of being selected in the sample
Expensive and time consuming
Needs a sampling frame
Aims:
To minimise random sampling error
To minimise systematic sampling bias
Introduction tosampling andProbability sampling designs
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Probability sampling designs
Simple random sampling
Systematic sampling
Stratified sampling
Cluster sampling
Multistage sampling
Introduction tosampling andSimple random sampling (SRS)
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Simple random sampling (SRS)
Definition: every population element, as well as sets
of elements, has the same probability of being
selected in the sample
Selection is done using a random device, such as a
pseudo-random number generator
Introduction tosampling andSimple random sampling (SRS)
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sampling andsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Simple random sampling (SRS)
Example
Suppose a population consists of 4 individuals:
Anna, Ben, Claire and David There are 6 possible samples of size n= 2 from a
population of size N= 4
Samples Probability
AB 1/6AC 1/6
AD 1/6
BC 1/6
BD 1/6
CD 1/6
The probability of each element (at the first draw) is
P(A) = P(B) = P(C) = P(D) = 1/4
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Introduction tosampling andFormulae for SRS
-
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p gsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Sample mean:
X=
n
i=1 Xi
n
Sample variance:
S2 =
n
i=1(Xi X)2n
1
Standard error of X:
S.E.(X) =n
Estimated standard error of X: ( unknown)
E.S.E.(X) =Sn
Introduction tosampling andSample size calculation
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p gsurvey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
p
Select the sample size such that the standard error
of a variable is less than or equal to some value k
n k n
k
2
Introduction tosampling andExample: Sample size how many
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
p p y
elements to select?
Population Size, N, Sample size, n
China > 1 billion ?UK 65 million ?City 4 million ?
Town 50,000 ?
Introduction tosampling andStratified random sampling
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
p g
This technique achieves greater accuracy by taking
advantage of known natural groupings of the
population
These are called strata and they should be chosenso that units are homogeneous (similar) within strata,
but heterogeneous (different) between strata
It makes use of SRS to sample units within strata
thus giving unbiased estimators
Introduction tosampling and
d iStratified random sampling
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Population elements are divided into strata (groups)
based on stratification factors (related to the
survey objectives)
Stratification factors should be relevant to the survey
(for example age, gender or social group)
Groups are homogeneous within and heterogeneousbetween groups
A number of elements ni is randomly selected from
each of the L strata, i = 1, . . . , L
Final sample size is
n= n1 + n2 + . . . + nL
where n1 is the number of elements selected from
stratum 1, etc.
Introduction tosampling andsurvey design
Example stratification factor: Age
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Population:Students of Market Research
Methods
N= N1 + N2 + N3
Stratum 1Age group
18-22N1
n1
Stratum 2Age group
22-26N2
n2
Stratum 3Age group
26+N3
n3
Introduction tosampling andsurvey design
Stratification sampling allocation
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Stratum Stratum Equal Weight Proportional
size allocation allocation
1 N1 = n1 = 250N1N
= 12 n1 = 500100,000
2 N2 = n2 = 250N2N
= 14 n2 = 250
50,0003 N3 = n3 = 250
N3N
= 18 n3 = 12525,000
4 N4 = n4 = 250N4N
= 18 n4 = 12525,000
N= n=1,000 n=1,000200,000
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Introduction tosampling andsurvey design
Stratified random sampling
-
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (ornon-random) sampling
Advantages:
Most precise and efficient random design (smallersampling errors)
Most representative, significant characteristics of thepopulation are represented adequately in the
different strata
Disadvantages:
Most expensive
Stratification information
Most difficult to administer
Introduction tosampling andsurvey design
Cluster sampling
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survey design
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Cluster sampling is aimed at economy (cost saving)
when the population is widely dispersed
The population is again subdivided, but this time into
clusters
Ideally the clusters are such that each is as variableas the main population and represents it well
Only a certain number of the clusters are sampled
using SRS sampling only a proportion of the
clusters is expected to result in economy
Within these randomly selected areas of clusters,
every unit is sampled
Introduction tosampling andsurvey design
Cluster sampling
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y g
Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Clusters should be heterogeneous
Suitable when sampling frame does not exist for the
whole population
Least efficient random design
When a subsample is taken from a selected cluster it
is called a multistage design
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Introduction tosampling andsurvey design
Systematic sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Systematic sampling is used when the units of the
population are ordered in some meaningful way
either in position or time
Units are sampled at equal distances throughout
the population and the first unit is sampled randomly
to give unbiasedness
This method can result in greater economy and
accuracy than other methods based on the same
sample size
Uses a sampling interval for selection, for example
elements 4, 44, 84, . . . , using sampling interval of 40
It is important to check how the list has been
compiled for any cyclicality
Introduction tosampling andsurvey design
Multistage sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
In multistage sampling, sample selection at two or
more successive stages
This technique is often adopted in large surveys
At the first stage, large compound units are sampled(primary units)
At the second stage, smaller units are sampled from
these (secondary units), and several samplingstages of this type may be performed until we at last
sample the basic units
Introduction tosampling andsurvey design
Multistage sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
This technique is commonly used in cluster sampling
so that we are at first sampling main clusters, and
then clusters within clusters, etc.
We can also use multistage sampling with mixed
techniques; i.e. cluster sampling at Stage 1, then
stratified sampling at Stage 2, etc.
Example: National survey of salesmen in a
company, sales areas could be identified
A random selection is taken of these, then instead ofinterviewing every person in the cluster, onlyrandomly selected people within the cluster will beinterviewed
Introduction tosampling andsurvey design
Non-probability (or non-random)
sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
sampling
Non-probability (or non-random) sampling
involves judgement or purposive sampling or expert
choice
Some units in the population do not have a chance of
selection
Individual units in the population do not have a
known chance of being selected
Introduction tosampling andsurvey design
Quota sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Quota sampling means selection is controlled to
some extent by stratification, weighting and the
settings of quotas for each stratum
Quotas are set by researchers
Selection of the respondents is the responsibility ofthe interviewers
Hence quota sampling is a type of stratified sampling
in which the selection of sampling units within strata(such as age, gender or social group) is done by
interviewers on a non-random basis, controlled by
quotas allocated to different strata
Introduction tosampling andsurvey design
Quota sampling
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
With quota sampling it is not possible to estimate the
sampling error
It is fast, cheap, and has administrative simplicity
The efficiency of the design depends on howrepresentative the sample is
Identify stratification factors that are important to thesubject of the survey
Proportions of factors within the sample shouldreflect their actual distribution in the population
Introduction tosampling andsurvey design
Quota sampling: example
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Control Population Sample
characteristic: composition composition Number
SexMale 48% 48% 480
Female 52% 52% 520
Total 100% 100% 1000
Introduction tosampling andsurvey design
Types of quota sampling
http://find/ -
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Independent quota sample results in biased
selection, hence is unreliable
The interviewer could fulfil the quota entirely fromone age group or social class
Interrelated quota sample controls the types of
respondents to be interviewed, hence is more
reliable
The interviewer has a more difficult job
Introduction tosampling andsurvey design
Types of quota sampling
http://find/ -
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
Random route or random walk
Start at specified points and call on households atspecified intervals expensive and inaccurate
Grid sampling
District selection based on ACORN classification http://acorn.caci.co.uk/
Region, television area, neighbourhood types
Introduction tosampling andsurvey design
Probability vs. non-probability
sampling designs
http://find/ -
7/28/2019 2 Introduction to Sampling and Survey Design
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Dr James Abdey
Overview
Stages of market research
Glossary
Sample surveys
Definitions
Survey objectives
Sampling frame
Statistics
Probability (or random)
sampling
Non-probability (or
non-random) sampling
sampling designs
Probability sampling makes it possible to estimate
the margins of sampling error
All statistical techniques can be applied
Non-probability sampling is sometimes more
convenient, cheaper and faster
http://find/ -
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