統計學 Fall 2004 授課教師 統計系余清祥 日期 2004年9月14日 第一週 什麼是統計 Slide 1

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1 Fall

2 ?, (Uncertainty), 2

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5 Chapter 1 Data and Statistics Applications in Business and Economics Data Data Sources Descriptive Statistics Statistical Inference 5

6 Applications in Business and Economics Accounting Public accounting firms use statistical sampling procedures when conducting audits for their clients. Finance Financial advisors use a variety of statistical information, including price-earnings earnings ratios and dividend yields, to guide their investment recommendations. Marketing Electronic point-of of-sale scanners at retail checkout counters are being used to collect data for a variety of marketing research applications. 6

7 Applications in Business and Economics Production A variety of statistical quality control charts are used to monitor the output of a production process. Economics Economists use statistical information in making forecasts about the future of the economy or some aspect of it. 7

8 Data Elements, Variables, and Observations Scales of Measurement Qualitative and Quantitative Data Cross-Sectional and Time Series Data 8

9 Data and Data Sets Data are the facts and figures that are collected, summarized, analyzed, and interpreted. The data collected in a particular study are referred to as the data set. 9

10 Elements, Variables, and Observations The elements are the entities on which data are collected. A variable is a characteristic of interest for the elements. The set of measurements collected for a particular element is called an observation. The total number of data values in a data set is the number of elements multiplied by the number of variables. 10

11 Data, Data Sets, Elements, Variables, and Observations Variables Company Dataram EnergySouth Keystone LandCare Psychemedics Observation Stock Annual Earn/ Exchange Sales($M) Sh.($) AMEX OTC NYSE NYSE AMEX Elements Data Set Datum 11

12 Scales of Measurement Scales of measurement include: Nominal( ) data are merely labels or assigned numbers Ordinal( ) data can be arranged in order such as worst to best or best to worst Interval data can be arranged in order and the difference between numbers has meaning Ratio data differ from interval data in that there is a definite zero point The scale determines the amount of information contained in the data. The scale indicates the data summarization and statistical analyses that are most appropriate. 12

13 Types of Data Numerical data Qualitative Data Types Quantitative Nominal Ordinal Levels of Measurement Interval Ratio Discrete Discrete or continuous 13

14 Scales of Measurement Nominal Data are labels or names used to identify an attribute of the element. A nonnumeric label or a numeric code may be used. 14

15 Scales of Measurement Nominal Example: Students of a university are classified by the school in which they are enrolled using a nonnumeric label such as Business, Humanities, Education, and so on. Alternatively, a numeric code could be used for the school variable (e.g. 1 denotes Business, 2 denotes Humanities, 3 denotes Education, and so on). 15

16 Scales of Measurement Ordinal The data have the properties of nominal data and the order or rank of the data is meaningful. A nonnumeric label or a numeric code may be used. 16

17 Scales of Measurement Ordinal Example: Students of a university are classified by their class standing using a nonnumeric label such as Freshman, Sophomore, Junior, or Senior. Alternatively, a numeric code could be used for the class standing variable (e.g. 1 denotes Freshman, 2 denotes Sophomore, and so on). 17

18 Scales of Measurement Interval The data have the properties of ordinal data and the interval between observations is expressed in terms of a fixed unit of measure. Interval data are always numeric. 18

19 Scales of Measurement Interval Example: Melissa has an SAT score of 1205, while Kevin has an SAT score of Melissa scored 115 points more than Kevin. 19

20 Scales of Measurement Ratio The data have all the properties of interval data and the ratio of two values is meaningful. Variables such as distance, height, weight, and time use the ratio scale. This scale must contain a zero value that indicates that nothing exists for the variable at the zero point. 20

21 Scales of Measurement Ratio Example: Melissa s s college record shows 36 credit hours earned, while Kevin s s record shows 72 credit hours earned. Kevin has twice as many credit hours earned as Melissa. 21

22 Qualitative and Quantitative Data Data can be further classified as being qualitative or quantitative. The statistical analysis that is appropriate depends on whether the data for the variable are qualitative or quantitative. In general, there are more alternatives for statistical analysis when the data are quantitative. 22

23 Qualitative Data Qualitative data are labels or names used to identify an attribute of each element. Qualitative data use either the nominal or ordinal scale of measurement. Qualitative data can be either numeric or nonnumeric. The statistical analysis for qualitative data are rather limited. 23

24 Quantitative Data Quantitative data indicate either how many or how much. Quantitative data that measure how many are discrete. Quantitative data that measure how much are continuous because there is no separation between the possible values for the data.. Quantitative data are always numeric. Ordinary arithmetic operations are meaningful only with quantitative data. 24

25 Cross-Sectional and Time Series Data Cross-sectional sectional data are collected at the same or approximately the same point in time. Example: data detailing the number of building permits issued in June 2000 in each of the counties of Texas Time series data are collected over several time periods. Example: data detailing the number of building permits issued in Travis County, Texas in each of the last 36 months 25

26 Data Sources Existing Sources Data needed for a particular application might already exist within a firm.. Detailed information is often kept on customers, suppliers, and employees for example. Substantial amounts of business and economic data are available from organizations that specialize in collecting and maintaining data. 26

27 Data Sources Existing Sources Government agencies are another important source of data, and the data types include census ( ) and survey ( ( ) data. Data are also available from a variety of industry associations and special-interest interest organizations. 27

28 Data Sources Internet The Internet has become an important source of data. Most government agencies, like the Bureau of the Census ( 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. 28

29 Data Sources 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. A survey is perhaps the most common type of observational study. 29

30 Data Acquisition Considerations 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. 30

31 Descriptive Statistics Descriptive statistics are the tabular, graphical, and numerical methods used to summarize data. 31

32 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 tune-ups ups performed in the shop. She examines 50 customer invoices for tune-ups. ups. The costs of parts, rounded to the nearest dollar, are listed below

33 Example: Hudson Auto Repair Tabular Summary (Frequencies and Percent Frequencies) Parts Percent Cost ($) Frequency Frequency Total

34 Example: Hudson Auto Repair Graphical Summary (Histogram) Frequency Parts Cost ($) 34

35 Example: Hudson Auto Repair Numerical Descriptive Statistics The most common numerical descriptive statistic is the average (or mean). Hudson s s average cost of parts, based on the 50 tune-ups ups studied, is $79 (found by summing the 50 cost values and then dividing by 50). 35

36 Statistical Inference Statistical inference is the process of using data obtained from a small group of elements (the sample) to make estimates and test hypotheses about the characteristics of a larger group of elements (the population). 36

37 Example: Hudson Auto Repair Process of Statistical Inference 1. Population consists of all tune-ups. ups. Average cost of parts is unknown. 2. A sample of 50 engine tune-ups ups is examined. 4. The value of the sample average is used to make an estimate of the population average. 3. The sample data provide a sample average cost of $79 per tune-up. up. 37

38 Population Verses a Sample Population (all votes cast) Sample (selected votes for observation) 38

39 Basic Definitions Descriptive Statistics ( ): the collection and description of data Inferential Statistics( ): analyzing, decision making or estimation based on the data Population( ): the set of all possible measurements that is of interest Sample( ): the portion of the population from which information is gathered 39

40 End of Chapter 1 40