Ch 2_Descriptive Stats Part 1 complete(1).pptx

Ch 2_Descriptive Stats Part 1 complete(1).pptx -...

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Descriptive Statistics Part 1 Summarizing Qualitative Data Summarizing Quantitative Data 1 D r . C . L i g h t n e r
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Summarizing Qualitative Data A frequency distribution is a tabular summary of data showing the frequency (or number) of items that appear in your data from each of several nonoverlapping classes. Frequency distributions provide quick (visual) insights that cannot be easily obtained by looking at the original data. 2 D r . C . L i g h t n e r
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Example: CLSU Algebra Course Students in a college Algebra course were asked to rate the overall effectiveness of the course as being excellent , above average , average , below average , or poor . The ratings provided by a sample of 20 students are shown below. Average Excellent Above Average Above Average Above Average Above Average Above Average Below Average Below Average Average Poor Average Above Average Average Above Average Average Above Average Below Average Above Average Poor 3 D r . C . L i g h t n e r
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Example: CLSU Algebra Course Frequency Distribution Rating Frequency Poor 2 Below Average 3 Average 5 Above Average 9 Excellent 1 Total 20 4 D r . C . L i g h t n e r
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Relative Frequency Distribution The relative frequency of a class is the fraction (or proportion) of the total number of data items belonging to the class. A relative frequency distribution is a tabular summary of data showing the relative frequency for each class. 5 D r . C . L i g h t n e r
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Percent Frequency Distribution The percent frequency of a class is the percentage of the total data items belonging to the class. A percent frequency distribution is a tabular summary of a set of data showing the percent frequency for each class. 6 D r . C . L i g h t n e r
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Example: CLSU Algebra Course Relative Frequency and Percent Frequency Distributions Relative Percent Rating Frequency Frequency Poor .10 10 Below Average .15 15 Average .25 25 Above Average .45 45 Excellent .05 5 Total 1.00 100 7 D r . C . L i g h t n e r
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Bar Graph A bar graph is a popular method used to display qualitative data. On the horizontal axis we specify the labels that are used for each class. A frequency , relative frequency , or percent frequency distribution can be used as the scale for the vertical axis. Using a bar of fixed width drawn above each class label, we extend the height of each bar to match the selected distribution for each class. The bars are separated to emphasize the fact that each class is a separate non-overlapping category. 8 D r . C . L i g h t n e r
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Example: CLSU: Bar Graph 9 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 Poor Poor Below Average Below Average Average Average Above Average Above Average Excellent Excellent Frequency Frequency D r .
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