Marketing Research Test 3 Chapters 9 10 11 12 14 Chapter 9 Developing the Sampling Plan A Introduction 1 If you collect information from or about each member of the relevant population you are conducting a census When the overall population is limited in size it is usually smart to attempt a census even if you can t get information from everyone 2 Sampling plan is the process of selecting the people of objects i e companies products etc to be surveyed interviewed or observed 3 With a sampling plan we collect information from a sample or subset of elements from the larger group of objects with the goal of making projections about what would be true for the population B Defining the Target Population overall group costly to obtain than is a census 1 Population all the individuals or objects that meet certain requirements for membership in the 2 We typically work with a sample rather than a census because a sample is often easier and less 3 Any population has certain characteristics these characteristics are called parameters and we assume that if we could take measurements of these characteristics from all population elements without any error we would know what is true about the population on these parameters 4 Statistics characteristics or measures of a sample to draw inferences about the larger population s parameters 5 Sampling error the difference between results obtained from a sample and results that would have been obtained had information been gathered from or about every member of the population C Identifying the Sampling Frame 1 Sampling frame the list of population elements from which a sample will be drawn the list could consist of geographic areas institutions individuals or other units 2 Unfortunately perfect sampling frames usually don t exist except in unusual circumstances That makes developing an acceptable sampling frame one of your most important and creative tasks 3 Sometimes you ll work with sampling frames that have been developed by companies that specialize in compiling databases and then selling the names addresses phone numbers and email addresses 4 Commonly used sampling frames include Customer databases Telephone directories Lists developed by data compilers D Selecting a Sampling Procedure 1 Nonprobability Samples involve personal judgment somewhere in the selection process Not all elements have an opportunity to be included so we can t estimate the probability that any particular element will be included in the sample As a result it s impossible to assess the degree of sampling error And that means that we can t say anything at all about what would have been true for the overall population we re stuck with sample statistics and don t know whether they apply to the population as a whole 2 Convenience samples people or objects are selected for the sample because they happen to be in the right place at the right time to be included Just go out and find a location where lost of people who are likely to be members of the population are located and do interviews or pass out surveys Commonly used for with exploratory research where the goal is to generate insights or to develop hypotheses Also called accidental sample EX television news question of the day polls 3 Judgment samples the sample elements are handpicked by the researcher because she believes that they can serve the research process EX hire panelists who are knowledgeable about the issue being researched rather than selecting them at random Snowball sample a judgment sample that is used to sample special populations in particular populations that are difficult to find and identify This type of judgment sample relies on the researcher s ability to locate an initial set of respondents with the desired characteristics These individuals are then asked to help identify others with the desired characteristics EX A demand study for a new product where initial respondents know people with a high interest level within the product category 4 Quota samples A nonprobability sample chosen so that the proportion of sample elements with certain characteristics is about the same as the proportion of the elements with the characteristics in the target population Stated more simply certain important characteristics of the population are represented proportionately in the sample EX Research problem investigate 100 undergraduate student attitudes toward a controversial new technology fee seniors and gender 50 female 50 male 10 students will interview 10 friends each for a total of 100 responses class 30 freshman 20 sophomores 30 Juniors 20 Known population parameters Approach 5 Probability Samples each member of the target population has a known nonzero chance of being included in the sample The chances of each member of the target population being included in the sample may not be equal but everyone has some chance of being included Because of this objectivity we can make inferences to the larger population based on the results from the sample and estimate the likely amount of sampling error 6 Simple random samples each unit included in the sample has a known and equal chance of being selected for study and every combination of population elements is a sample possibility Walking down the street and passing out surveys to unknown people at random is random in the everyday sense but not random in a scientific sample sense EX Sample is drawn by a computer or from a physical list using a random number table 7 Systematic sample a probability sampling plan in which every kth element in the population is selected for the sample pool after a random start Calculating the sampling interval i e k the number of names to count when selecting the same members in general we simply divide the number of population elements in the sampling frame by the number of elements that we need to draw to obtain the sample size we want EX Example Research Problem Investigate 250 undergraduate student attitudes toward controversial new technology fee 5000 students published in the campus directory Known Population Approach k 5000 250 20 or 1 out of every 20 students on campus will be surveyed Randomly select the first name then count down 20 names Select that person to be surveyed and then count down 20 names again Select that person and so on until you get 250 names Total Sampling Elements TSE the number of population elements that must be drawn from the population and included in the initial sample pool in order to end up with the desired
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