Marketing Research

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Marketing Research

• Aaker, Kumar, Day
• Seventh Edition
• Instructors Presentation Slides

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Chapter Fourteen

• Sampling Fundamentals

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Sampling Fundamentals

• When Is Census Appropriate?
• Population size itself is quite small
• Information is needed from every individual in
  the population
• Cost of making an incorrect decision is high
• Sampling errors are high

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Sampling Fundamentals (Contd.)

• When Is Sample Appropriate?
• Sample size is large
• Both cost and time associated with obtaining
  information from the population is high
• Quick decision is needed
• In a given time period, more time can be spent on
  each interview, thereby increasing response
  quality

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Sampling Fundamentals (Contd.)

• When Is Sample Appropriate? (Cont.)
• Easier to manage surveys of smaller samples and
  also exercise quality control in the interview
  process
• Population being dealt with is homogeneous
• Used if census is impossible

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Error in Sampling

• Total Error
• Difference between the true value and the
  observed value of a variable
• Sampling Error
• Error is due to sampling
• Non-sampling Error
• Error is observed in both census and sample
• Measurement Error
• Data Recording Error
• Data Analysis Error
• Non-response Error

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Sampling Process

• Determining Target Population
• Well thought out research objectives
• Consider all alternatives
• Know your market
• Consider the appropriate sampling unit
• Specify clearly what is excluded
• Should be reproducible
• Convenience

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Sampling Process (Contd.)

• Determining Sampling Frame
• Creating lists
• Selection A Sampling Procedure
• Choose between Bayesian and traditional sampling
  procedure
• Decide whether to sample with or without
  replacement

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Identifying the Target Population
Reconciling the Population, Sampling Frame
Differences
Determining the Sampling Frame
Selecting a Sampling Frame
Probability Sampling
Non-Probability Sampling
The Sampling Process
Determining the Relevant Sample Size
Execute Sampling
Data Collection From Respondents
Handling the Non-Response Problem
Information for Decision-Making
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Sampling Techniques

• Probability Sampling
• All population members have a known probability
  of being in the sample
• Simple Random Sampling
• Each population member, and each possible sample,
  has equal probability of being selected
• Stratified Sampling
• The chosen sample is forced to contain units from
  each of the segments or strata of the population

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Sampling Techniques (Contd.)

• Types of Stratified Sampling
• Proportionate Stratified Sampling
• Number of objects/sampling units chosen from each
  group is proportional to number in population
• Can be classified as directly proportional or
  indirectly proportional stratified sampling
• Disproportionate Stratified Sampling
• Sample size in each group is not proportional to
  the respective group sizes
• Used when multiple groups are compared and
  respective group sizes are small

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Sampling Techniques (Contd.)

• Cluster Sampling
• Involves dividing population into subgroups
• Random sample of subgroups/clusters is selected
  and all members of subgroups are interviewed
• Very cost effective
• Useful when subgroups can be identified that are
  representative of entire population

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Sampling Techniques (Contd.)

• Systematic Sampling
• Involves systematically spreading the sample
  through the list of population members
• Commonly used in telephone surveys
• Non Probability Sampling
• Costs and trouble of developing sampling frame
  are eliminated
• Results can contain hidden biases and
  uncertainties

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Sampling Techniques (Contd.)

• Types of Non Probability Sampling
• Judgmental
• "Expert" uses judgement to identify
  representative samples
• Snowball
• Form of judgmental sampling
• Appropriate when reaching small, specialized
  populations
• Each respondent, after being interviewed, is
  asked to identify one or more others in the
  appropriate group

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Sampling Techniques (Contd.)

• Convenience
• Used to obtain information quickly and
  inexpensively
• Quota
• Minimum number from each specified subgroup in
  the population
• Often based on demographic data

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Non Response Problems

• Respondents may
• Refuse to respond
• Lack the ability to respond
• Be inaccessible

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Non Response Problems (Contd.)

• Sample size has to be large enough to allow for
  non response
• Those who respond may differ from non respondents
  in a meaningful way, creating biases
• Seriousness of nonresponse bias depends on extent
  of non response

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Solutions to Nonresponse Problem

• Improve research design to reduce the number of
  nonresponses
• Repeat the contact one or more times (call back)
  to try to reduce nonresponses
• Attempt to estimate the nonresponse bias

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Shopping Center Sampling

• 20 of all questionnaires completed or interviews
  granted are store-intercept interviews
• Bias is introduced by methods used to select

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Shopping Center Sampling (Contd.)

• Source of Bias
• Selection of shopping center
• Point of shipping center from which respondents
  are drawn
• Time of day
• More frequent shoppers will be more likely to be
  selected

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Shopping Center Sampling (Contd.)

• Solutions to Bias
• Shopping Center Bias
• Use several shopping centers in different
  neighborhoods
• Use several diverse cities
• Sample Locations Within a Center
• Stratify by entrance location
• Take separate sample from each entrance
• To obtain overall average, strata averages should
  be combined by weighing them to reflect traffic
  that is associated with each entrance

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Time Sampling

• Stratify by time segments
• Interview during each segment
• Final counts should be weighed according to
  traffic counts

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Sampling in an International Context

• Major Problems
• Absence of information on sample frames in other
  countries
• Sampling equivalence

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Sampling Procedure

• Decide whether research will be conducted in all
  countries or is generalizable from one country to
  another
• Non-probability sampling is more frequently used
  than probability sampling because of lack of
  information
• Snowball sampling technique is very popular

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Sampling Procedure (Cont.)

• Two phase sampling is used to reduce costs
• Researcher must decide whether to use the same
  sampling procedure across all countries
• Consider relative cost, reliability and accuracy
• In determining sample size, researcher must
  consider cost and availability of population data