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Unformatted text preview: Chapter 2: Descriptive Analysis and Presentation of Single Variable Data • In Chapter 1 we discussed basics of collecting data • Now what? • Descriptive Statistics • Overview Initially – we will look at just 1 variable A) Summary Graphs Variables can be classified into several categories Variable Quantitative Qualitative Numerical Value Attribute: How you summarize data depends on variable type . Qualitative Data (Nominal and Ordinal) • Often use Circle Graphs and Bar Graphs to show data • Both show relative proportions in various categories Circle Graph Bar Graph Summary Graphs: Qualitative Data Graph can show frequency or relative frequency • both provide similar information • Frequency = the NUMBER of observations in each category • Relative Frequency = the PERCENT of observations in that category Summary Graphs: Qualitative Data Graphs look similar – you decide what you want to present Qualitative Data Display: Circle Graph Summary Graphs: Qualitative Data • green 14 • purple 2 • red 6 • yellow 14 Summary Graphs: Qualitative Data Bar Graph What about Quantitative Data? Variable Quantitative Qualitative Circle graphs Bar graphs Sample Quantitative Data Set • Weight of Black Labs at the Smith Pet Shelter Observation Weight (lbs) 1 62 2 92 3 53 4 64 5 54 6 86 7 75 8 68 Summary Graphs: Quantitative Data Quantitative Data • Simplest: StemandLeaf Diagram Summary Graphs: Quantitative Data 6 3,4,7,8 7 5,5,5,7,8 8 4,6 9 2,9 Quantitative Data: Frequency Distributions and Frequency Histograms • Data set: 0, 0, 1, 1, 1, 2, 2, 3, 3, 3, 3, 3, 4, 4, 5 • f = represents the frequency • x=represents the variable • class = each stem in the stem and leaf plot represents a class; class should not overlap x f 2 1 3 2 2 3 5 4 2 5 1 6 Summary Graphs: Quantitative Data Grouping Data • If too many classes to deal with – then group data • Classes can not overlap • Every data set different, but good approach is usually: • # classes = √ n Summary Graphs: Quantitative Data Frequency Histogram for Final Grades of Biometrics Students Fall 2005 1 6 10 5 6 2 4 6 8 10 12 5059 6069 7079 8089 90100 Grade Category Frequency Summary Graphs: Quantitative Data Can also show same information as a Relative Frequency Histogram Class Frequency Relative Frequency 5059 1 0.04 6069 6 0.21 7079 10 0.36 8089 5 0.18 90100 6 0.21 Total (Σ n ) = 28 Σ = 1.0 When calculating relative frequencies, go to 2 decimal places Summary Graphs: Quantitative Data Relative Frequency Histogram Relative Frequency Histogram for Biom 301 Final Grades, Fall 2005 0.04 0.21 0.36 0.18 0.21 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 5059 6069 7079 8089 90100 Exam Grades Relative Frequency Shape identical to Frequency Histogram Summary Graphs: Quantitative Data So the shape of your histogram provides information • Need to be able to describe shapes • Symmetric: • Examples Or Frequency Frequency value value 100 100 Summary Graphs: Quantitative Data •...
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This document was uploaded on 11/04/2011 for the course BIOM 301 at Maryland.
 Fall '08
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