HBM221N Sampling

7/28/2019 HBM221N Sampling

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Sampling Fundamentals


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Steps intheSamplingProcess


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Sample or Census

Population

(Census)

Sample

An aggregate of all the elementsthat share some common set of

characteristics and that comprisethe universe for the purpose of the

marketing research problem.

A subgroup of the populationselected for

participation inthe study .


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Sampling Terms

Census - count of the populationSample - subset of the population

Sample Unit/Element - basic level of investigation i.e.:

Household, Person, BusinessSampling Frame - a master list of the all sample unitswithin the population

i.e.: Telephone Book, List of registered businesses within anindustry


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Sample or CensusWhen is a censusappropriate?

population is small

information required from

everyone in populationcost of incorrect decisionis high

sampling errors are high

When is a sampleappropriate?

population is large

quick decision is needed

cost is an issue

improved quality

homogeneous population

census is not possible


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A precise statement of who should and should not beincluded in the sample

Do we only want to interview those that participate in sportat the professional level? Should we ignore amateur sportspeople?

Elements

An element about which or from which the information is desired.

eg. Respondent - male, female, over 18, main grocery buyer,decision maker for a new product

The Target Population


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Selecting a Sampling Procedure

Probability sample All population members have a knownprobability of being selected in thesample

Nonprobability sampleProbability is unknown, based on

convenience/judgement


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Probability Sampling

Simple random sampling

Systematic sampling

Stratified samplingCluster sampling


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Simple Random Sampling

Researcher uses:Random number tables

Random digit dialing

Some other randomselection procedure

Guarantees that eachmember of the populationhas an equal chance of selection


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Table of random numbers


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Systematic Sampling

Researcher selects astarting point (usually bySRS)

Then a constant skip intervalis used to select every other member

The skip interval used mustcover the entire pop

regardless of starting pointIs more efficient than SRS


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Tennis magazine conducted a mail survey of its subscribers to gain a better understanding of its market. Systematic sampling was employed to select asample of 1,472 subscribers from the publication's domestic circulation list.If we assume that the subscriber list had 1,472,000 names, the samplinginterval would be 1,000 (1,472,000/1,472). A number from 1 to 1,000 wasdrawn at random. Beginning with that number, every 1,000th subscriber wasselected.

A brand-new dollar bill was included with the questionnaire as an incentive to

respondents. An alert postcard was mailed one week before the survey. Asecond, follow-up, questionnaire was sent to the whole sample ten days after the initial questionnaire. There were 76 post office returns, so the neteffective mailing was 1,396. Six weeks after the first mailing, 778 completedquestionnaires were returned, yielding a response rate of 56%.

Tennis's Systematic SamplingReturns a Smash


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Stratified Sampling

Proportionate stratified samplingnumber selected from each strata is proportional tonumber in total population

Disproportionate stratified samplingsample size in each group is proportional to therespective strata size


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Random samplefrom each stratum

Not necessary todraw the samenumber from eachstratum


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Non-probability Sampling

Judgemental sampling judgement used to identify representative samples

Snowball samplingform of judgement sampling

appropriate for small specialised population

each respondent is asked to identify others in group


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Non-probability SamplingConvenience sampling

respondents selected conveniently

inexpensive

quick

Quota samplingminimum number from each specified subgroup in thepopulation

often based on demographics


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Sample Sizes Used in Marketing Research Studies

Type of Study Minimum Size Typical Range

Problem identification research(e.g. market potential)

500 1,000-2,500

Problem-solving research (e.g.

pricing)

200 300-500

Product tests 200 300-500

Test marketing studies 200 300-500

TV, radio, or print advertising (percommercial or ad tested)

150 200-300

Test-market audits 10 stores 10-20 stores

Focus groups 2 groups 4-12 groups


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Qualitative factors: Determining the Sample Size

Importance of the decision

Number of variables

Nature of the analysis

Sample size used in similar studies

Incidence rates

Completion rates

Resource constraints

Anticipated refusals


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Sampling and non sampling errors

Error can occur from the sampling processsampling error

and from other issues that are not associated with thesampling for the survey

non sampling errors.

response and non-response errors. non-sampling error largely occurs during the process of collecting the data.


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Non-response Problems

Due torefusal to respond

inability to respond

not at home/inaccessibleReduced by

improving the researchdesign

call-backs

Every effort should be madeto reduce these kinds of errorsas they are the easiest tominimise

The researcher and theinterviewer need to beprofessional and familiar withthe processes


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A sample is almost always more desirable than a censusbecause:

Cost - populations are often very large and taking acensus is expensive

Time - because of the numbers in a population it can takea very long time to access each sample unit

Analysis - typically researchers and research firms cannotprocess the huge amounts of data generated by a census

Non-sampling Error - Census can have very high non-

sampling errors when compared to sampling error, thusaccuracy can be better in a sample

Secrecy - often marketing research is done for competitiveadvantage


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Summarydistinguish between a census and a sample

describe the steps in the sampling process

define the appropriate target population for a given researchproblem

identify and evaluate alternative sampling frames for atarget population

differentiate between probability and non-probabilitysampling techniques

assess non-response problems in sampling


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For you to answer

True or false.If a researcher wanted a sample of 100

people based on a sampling frame of 10,000 people whoare subscribers to a magazine, they should sample every200th person on the list.

Sampling error is:

a) The difference between the population parameter and thesample parameter as a result of sampling

b) Error that occurs when the researcher incorrectly definesthe constructs of the study

c) Error that occurs as a result of incorrectly defining theresearch objectives

d) All of the above


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And more Which of the following best describes the sample for a shoppingmall intercept:

a) A random sampleb) A probability samplec) A non probability sample

d) None of the above

Which of the following sets of sampling techniques contains onlyprobability sampling techniques?

a) systematic sampling, quota sampling, snowball samplingb) cluster sampling, quota sampling, snowball samplingc) proportionate stratified sampling, quota sampling, snowball

sampling

d) None of the above

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HBM221N Sampling