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Unformatted text preview: ing and maintaining data. Slide 29 Data Sources s Existing Sources • Government agencies are another important source of data. • Data are also available from a variety of industry associations and special­interest organizations. Slide 30 Data Sources s Internet • The Internet has become an important source of data. • Most government agencies, like the Bureau of the Census (www.census.gov), make their data available through a web site. • More and more companies are creating web sites and providing public access to them. • A number of companies now specialize in making information available over the Internet. Slide 31 Data Sources s Statistical Studies • Statistical studies can be classified as either experimental or observational. • In experimental studies the variables of interest are first identified. Then one or more factors are controlled so that data can be obtained about how the factors influence the variables. • In observational (nonexperimental) studies no attempt is made to control or influence the variables of interest; an example is a survey. Slide 32 Data Acquisition Considerations s s s Time Requirement • Searching for information can be time consuming. • Information might no longer be useful by the time it is available. Cost of Acquisition • Organizations often charge for information even when it is not their primary business activity. Data Errors • Using any data that happens to be available or that were acquired with little care can lead to poor and misleading information. Slide 33 Descriptive Statistics s Descriptive statistics are the tabular, graphical, and numerical methods used to summarize data. Slide 34 Example: Hudson Auto Repair The manager of Hudson Auto would like to have a better understanding of the cost of parts used in the engine tune­ups performed in the shop. She examines 50 customer invoices for tune­ups. The costs of parts, rounded to the nearest dollar, are listed below. 91 71 104 85 62 78 69 74 97 82 93 72 62 88 98 57 89 68 68 101 75 66 97 83 79 52 75 105 68 105 99 79 77 71 79 80 75 65 69 69 97 72 80 67 62 62 76 109 74 73 Slide 35 Example: Hudson Auto Repair s Tabular Summary (Frequencies and Percent Frequencies) Par...
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