Marketing Research MAR4613 Test 2 Review Chapter 11 Sampling Design and Procedures Ch 14 Sample or Census o Population the aggregate of all the elements that shares some set of characteristics and that comprise the universe for the purposes of the marketing research problem population parameters are usually numbers Population parameters can be calculated directly in a straightforward way after the census is Information about population parameters may be obtained by a census sample involves a complete enumeration of the elements of a population o Census enumerated o Sample a subgroup of the population selected for participation in the study Sample characteristics aka statistics are then used to make inferences about the population parameters Inferences linking sample characteristics and population parameters are estimation procedures and tests of hypotheses o Conditions Favoring the use of Sample vs Census 1 Budget 2 Time available 3 Population size 4 Variance in the characteristic 5 Cost of sampling errors 6 Cost of nonsampling errors 7 Nature of measurement 8 Attention to individual cases Small Short Large Small Low High Destructive Yes Large Long Small Large High Low Nondestructive No Census is both costly time consuming to conduct unrealistic if the population s large most consumer products vs industrial products which are small if cost of sampling error s high census is preferred eliminates those errors can greatly increase nonsampling error to the point that they exceed sampling errors of a sample Sampling s preferred when the cost of nonsampling error s high in most cases accuracy considerations favor samples over census may be preferred if the measurement process results in the destruction contamination of elements sampled may also be necessary to focus attention on individual cases other pragmatic considerations like keeping the study secret may favor a sample Nonsampling errors are found to be the major contributor to total error whereas random sampling errors have been relatively small in magnitude The Sampling Design Process includes 5 steps which are closely interrelated relevant to all aspects of the marketing research process sample design decisions should be integrated with all other decisions in a research process 1 Define the target population 2 determine the sampling frame 3 select a sampling technique s 4 determine the sample size 5 execute the sampling process o 1 Define the Target Population the collection of elements or objects that possesses the information sought by the researcher and about which inferences are to be made Must be precisely defined imprecise definition will lead to ineffective misleading research Involves translating the problem definition into a precise statement of who should and shouldn t be included in the sample Should be defined in terms of elements sampling units extent and time Element an object that possesses the information sought by the researcher the basic unit containing the elements of the population to be sampled Sampling unit 1 Extent the geographical boundaries Time time period under consideration o Determine the Sampling Frame a representation of the elements of the target population consists of a list or set of directions for identifying the target population Ex telephone book association directory listing of firms in an industry mailing list bought from a commercial organization city directory or a map if a list cant be compiled then at least some directions for identifying the target population should be specified It s often possible to compile obtain a list of population elements but it may omit some elements of the population or include others that don t belong therefore use of a list will lead to sampling frame error Discrepancy between population and sampling frame may be small in some cases but in most cases researcher should recognize treat sampling frame error can be done in 1 of 3 ways 1 Can redefine population in terms of the sampling frame this approach s simplistic but prevents the researcher from being misled about the actual population being investigated 2 Screening the respondents in the data collection phase can eliminate inappropriate elements contained in the sampling frame but can t account for elements that have been omitted 3 Adjusting the data collected by a weighting scheme to counterbalance the sampling frame error o Select a Sampling Technique involves deciding between a Bayesian or traditional sampling approach to sample with or without replacement and to use nonprobability or probability sampling Bayesian sampling approach selection method in which the elements are selected sequentially explicitly incorporates prior information about population parameters as well as the costs and probabilities associated with making wrong decisions Not used widely because much of the required information on costs and probabilities isn t available Traditional sampling approach entire sample s selected before data collection begins most commonly used sampling technique in which an element can be included in the Sampling with replacement sample more than once element s selected appropriate data s obtained then element s placed back in the sampling frame possible for an element to be included in the sample more than once Sampling without replacement the sample more than once once an element s selected for inclusion in the sample it s removed from the sampling frame and therefore can t be selected again Statistics calculations are done somewhat differently for the 2 approaches but statistical inference isn t very different if the sampling frame s large relative to the ultimate sample size distinction s important only when the sampling frame s not large compared to sample size sampling technique in which an element can t be included in Most important choice about technique is that of using probability or nonprobability sampling If sampling unit s different from element it s necessary to specify precisely how the elements within the sampling unit should be selected Commonly more than 1 person in a household may qualify when a probability sampling technique s being employed a random selected must be made from all eligible persons in each household a simple procedure is the next birthday method interviewer asks which of the eligible persons in the household has the next birthday and includes that person in the sample o Determine the Sample Size number of elements to be included in a study Qualitative factors that
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