chapter 2 - Chapter 2: Descriptive Analysis and...

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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: Stem-and-Leaf 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 50-59 60-69 70-79 80-89 90-100 Grade Category Frequency Summary Graphs: Quantitative Data Can also show same information as a Relative Frequency Histogram Class Frequency Relative Frequency 50-59 1 0.04 60-69 6 0.21 70-79 10 0.36 80-89 5 0.18 90-100 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 50-59 60-69 70-79 80-89 90-100 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.

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chapter 2 - Chapter 2: Descriptive Analysis and...

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