Lecture_03,_Chap_2,_Sec_2b,_4

Lecture_03,_Chap_2,_Sec_2b,_4 - Organizing Quantitative...

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Organizing Quantitative Data (continuing from last class) Learning objectives Organize discrete data in tables Construct histograms of discrete data Organize continuous data in tables Construct histograms of continuous data Draw stem-and-leaf plots Draw dot plots Identify the shape of a distribution 1 2 3 5 4 7 6
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Organizing Quantitative Data Continuous data cannot be put directly into frequency tables since they do not have any obvious categories Categories are created using classes , or intervals of numbers The continuous data is then put into the classes
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Organizing Quantitative Data For ages of adults, a possible set of classes is 20 – 29 30 – 39 40 – 49 50 – 59 60 and older For the class 30 – 39 30 is the lower class limit 39 is the upper class limit
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Organizing Quantitative Data The class width is the difference between consecutive lower class limits For the class 30 – 39, the class width is 40 – 30 = 10 Why isn’t the class width 39 – 30 = 9? The class 30 – 39 years old actually is 30 years to 39 years 364 days old … or 30 years to just less than 40 years old The class width is 10 years, all adults in their 30’s
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Organizing Quantitative Data All the classes (20 – 29, 30 – 39, 40 – 49, 50 – 59) all have the same widths, except for the last class The class “60 and above” is an open-ended class because it has no upper limit Classes with no lower limits are also called open-ended classes
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Organizing Quantitative Data The classes and the number of values in each can be put into a frequency table In this table, there are 1147 subjects between 30 and 39 years old Age Number 20 – 29 533 30 – 39 1147 40 – 49 1090 50 – 59 493 60 and older 110 Helpful Hint : Read carefully and memorize all the terms presented on p. 79 of your textbook.
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Organizing Quantitative Data Good practices for constructing tables for continuous variables: The is no unique way of selecting classes! The classes should not overlap The classes should not have any gaps between them The classes should have the same width (except for possible open-ended classes at the extreme low or extreme high ends) The lower class boundaries should be “reasonable” numbers The class width should be a “reasonable” number
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Organizing Quantitative Data To construct a frequency distribution: 1. Select number of classes desired 2. Choose class width 3. Choose class limits 4. Count number of measurements per class 5. List the classes and frequencies in a table
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Organizing Quantitative Data Example 1 The volume of a stock is the number of shares traded on a given day. The following data, in millions, so that 3.78 represents 3,780,000 shares traded, represents the volume of Altria Group stock traded for a random sample of 35 trading days. The data is presented on the next slide. Construct a frequency distribution
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Organizing Quantitative Data Example 1 (cont.) Volume of Altrea Group stock (in millions) 3.78 8.74 4.35 5.02 8.4 6.06 5.75 5.34 6.92 6.23 5.32 3.25 6.57 7.57 6.07 3.04 5.64 5 7.16 4.88 10.32 3.38 7.25 6.52 4.43 3.38 5.53 4.74 9.7 3.56 10.96 4.5 7.97 3.01 5.58
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This note was uploaded on 08/04/2008 for the course STAT 250 taught by Professor Sims during the Spring '08 term at George Mason.

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Lecture_03,_Chap_2,_Sec_2b,_4 - Organizing Quantitative...

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