Marketing Research Aaker, Kumar, Day Seventh Edition Instructor’s Presentation Slides

Chapter Fourteen Sampling Fundamentals

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day Identifying the Target Population Determining the Sampling Frame Selecting a Sampling Frame Probability Sampling Non-Probability Sampling Determining the Relevant Sample Size Execute Sampling Data Collection From Respondents Information for Decision-Making Reconciling the Population, Sampling Frame Differences Handling the Non- Response Problem The Sampling Process

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day Non Response Problems Respondents may: Refuse to respond Lack the ability to respond Be inaccessible

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day Shopping Center Sampling 20% of all questionnaires completed or interviews granted are store-intercept interviews Bias is introduced by methods used to select

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day Time Sampling Stratify by time segments Interview during each segment Final counts should be weighed according to traffic counts

© Marketing Research 7th EditionAaker, Kumar, Day Sampling in an International Context Major Problems: Absence of information on sample frames in other countries Sampling equivalence

© Marketing Research 7th EditionAaker, Kumar, Day 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

© Marketing Research 7th EditionAaker, Kumar, Day 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