BUS152-Ch07 - BUS152 - Statistics for Social Sciences...

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Chapter 7: Sampling and Sampling Distributions BUS152 - Statistics for Social Sciences Spring 2011
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Why Sample? Selecting a sample is less time- consuming than selecting every item in the population (census). Selecting a sample is less costly than selecting every item in the population. An analysis of a sample is less cumbersome and more practical than an analysis of the entire population. Chap 7-2
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A Sampling Process Begins With A Sampling Frame The sampling frame is a listing of items that make up the population Frames are data sources such as population lists, directories, or maps Inaccurate or biased results can result if a frame excludes certain portions of the population Using different frames to generate data can lead to dissimilar conclusions Chap 7-3
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Types of Samples Samples Non-Probability Samples Judgment Probability Samples Simple Random Systematic Stratified Cluster Convenience Chap 7-4
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Types of Samples: Nonprobability Sample In a nonprobability sample, items included are chosen without regard to their probability of occurrence. In convenience sampling , items are selected based only on the fact that they are easy, inexpensive, or convenient to sample. In a judgment sample, you get the opinions of pre- selected experts in the subject matter. Chap 7-5
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Types of Samples: Probability Sample In a probability sample , items in the sample are chosen on the basis of known probabilities. Probability Samples Simple Random Systematic Stratified Cluster Chap 7-6
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Probability Sample: Simple Random Sample Every individual or item from the frame has an equal chance of being selected Selection may be with replacement (selected individual is returned to frame for possible reselection) or without replacement (selected individual isn’t returned to the frame). Samples obtained from table of random numbers or computer random number generators. Chap 7-7
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Selecting a Simple Random Sample Using A Random Number Table Sampling Frame For Population With 850 Items Item Name Item # Bev R. 001 Ulan X. 002 . . . . . . . . Joann P. 849 Paul F. 850 Portion Of A Random Number Table 49280 88924 35779 00283 81163 07275 11100 02340 12860 74697 96644 89439 09893 23997 20048 49420 88872 08401 The First 5 Items in a simple random sample Item # 492 Item # 808 Item # 892 -- does not exist so ignore Item # 435 Item # 779 Item # 002 Chap 7-8
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Probability Sample: Systematic Sample Decide on sample size: n Divide frame of N individuals into groups of k individuals: k = N / n Randomly select one individual from the 1 st group Select every k th individual thereafter N = 40 n = 4 k = 10 First Group Chap 7-9
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Probability Sample: Stratified Sample Divide population into two or more subgroups (called strata ) according to some common characteristic A simple random sample is selected from each subgroup, with sample sizes proportional to strata sizes
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BUS152-Ch07 - BUS152 - Statistics for Social Sciences...

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