Presentation on theme: "Organization and description of data"— Presentation transcript:
1 Organization and description of data Chapter 2Organization and description of data
2 Box on Page 24 Describing a Data Set of Measurements
3 Types of data Qualitative or categorical data Numerical or measurement dataWe will use the term numerical-valued variable or just variable to refer to a characteristic that is measured on a numerical scale.Two type of variables:DiscreteContinuous
4 Categorical dataEach observation is recorded as a member of one of several categories.Data are organized in the form of a frequency table that shows the frequencies of the individual categories.Further, proportions of observations in each category are calculated:An example in the next slide.
9 Line Diagrams and Histograms The distinct values of the variable are located on the horizontal axis.Draw a vertical rectangle (line) at each value and make the height equal to the relative frequency.Figure 2.4 (p. 29) Graphic display of the frequency distribution of data in Table 3.
10 Figure 2.5 (p. 30) Dot diagram for the heart transplant data. Data on a continuous variableFor small data set, a dot diagram can be used; individual measurements are plotted above a line as prominent dots.Example:Figure 2.5 (p. 30) Dot diagram for the heart transplant data.The second method is frequency distribution on intervals; used when the data consist of a large number of measurements.
11 Box on Page 30 Constructing a Frequency Distribution for a Continuous Variable
12 Table 2.4 (p. 32) The Data of Forty Cash Register Receipts (in Dollars) at a University Bookstore
13 Table 2.5 (p. 33) Frequency Distribution for Bookstore Sales Data
14 Presenting a frequency distribution as a histogram Mark the class intervals on a horizontal axisOn each interval, draw a vertical rectangle whose area represents the relative frequencyHeight of the rectangle = Relative frequency / width of intervalThe total are of a histogram is 1.
15 Figure 2.7 (p. 34) Histogram of the bookstore sales data of Tables 4 and 5. Sample size = 40.
16 Figure 2.8 (p. 35) Population tree (histograms) of the male and female age distributions in the US in (Source: US Bureau of the Census.)
17 Table 2.6 (p. 35) Examination Scores of 50 Students A stem-and-leaf display provides a more efficient variant of the histogram for displaying data, especially when the observations are two-digit numbers.Example:Table 2.6 (p. 35) Examination Scores of 50 Students
18 Table 2.7 (p. 35) Stem-and-Leaf Display for the Examination Scores