Chapters 10 11 and 12

# Chapters 10 11 and 12 - Chapters 10,11 and 12(Student...

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Chapters 10,11, and 12 (Student) 1 Graphs, Good and Bad Recall the definition of statistics: Statistics is the science of collecting, classifying , presenting , and interpreting data. Types of Variables Quantitative variable – takes numerical values for which arithmetic operations make sense. Examples: amount of money, number of children, distance Categorical variable – places an individual into one of several groups or categories Examples: gender, race, academic major, zip code Distribution of a Variable The distribution of a variable tells us what values it takes and how often each value occurs. How do we describe distributions? Tables or graphs Numerical summaries There are several graphical (pictorial) ways to describe/display distributions. The method used is determined by the type of variable (data) and the idea to be presented.

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Chapters 10,11, and 12 (Student) 2 Tables and Graphs for Categorical Data • Frequency (count) – the number of times a value of a variable occurs in the data Relative Frequency – the proportion (fraction or percent) of all observations that have a given value Example: Table of Exam 1 Grades 4% 0.04 7 F 10% 0.10 20 D 12% 0.12 24 C 26% 0.26 51 B 48% 0.48 95 A Percentage Relative Frequency Frequency Grade Graphs for Categorical Data Basic graphs for summarizing categorical variables (data) are pie charts and bar graphs. Pie chart – shows the amount of data that belongs to each category as a proportional part of a circle.