Chapter01

The Basic Practice of Statistics (Paper) & Student CD

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Unformatted text preview: Displaying data with graphs BPS chapter 1 © 2006 W. H. Freeman and Company Objectives (BPS chapter 1) Picturing Distributions with Graphs Individuals and variables Two types of data: categorical and quantitative Ways to chart categorical data: bar graphs and pie charts Ways to chart quantitative data: histograms and stemplots Interpreting histograms Time plots Individuals and variables Individuals are the objects described by a set of data. Individuals may be people, but they may also be animals or things. Example: Freshmen, 6-week-old babies, golden retrievers, fields of corn, cells A variable is any characteristic of an individual. A variable can take different values for different individuals. Example: Age, height, blood pressure, ethnicity, leaf length, first language Two types of variables A variable can be either quantitative Something that can be counted or measured for each individual and then added, subtracted, averaged, etc., across individuals in the population. Example: How tall you are, your age, your blood cholesterol level, the number of credit cards you own. or categorical Something that falls into one of several categories. What can be counted is the count or proportion of individuals in each category. Example: Your blood type ( A, B, AB, O ), your hair color, your ethnicity, whether you paid income tax last tax year or not. How do you decide if a variable is categorical or quantitative? Ask: What are the n individuals/units in the sample (of size “ n ”)? What is being recorded about those n individuals/units? Is that a number ( quantitative) or a statement ( categorical)? 69 Diabetes Patient G 73 Accident Patient F 80 Heart disease Patient E 60 Lung cancer Patient D 75 Stroke Patient C 70 Stroke Patient B 56 Heart disease Patient A AGE AT DEATH DIAGNOSIS Individuals in sample Quantitative Each individual is attributed a numerical value Categorical Each individual is assigned to one of several categories Apply your knowledge Go to page 6 and work on the following problems: 1.1 Fuel economy 1.2 Students and TV Apply your knowledge Go to page 6 and work on the following problems: 1.1 Fuel economy 1.2 Students and TV Ways to chart categorical data Because the variable is categorical, the data in the graph can be ordered any way we want (alphabetical, by increasing value, by year, by personal preference, etc.). Bar graphs Each category is represented by a bar. Pie charts Peculiarity: The slices must represent the parts of one whole. Example: Top 10 causes of death in the United States, 2001 26% 629,967 All other causes 1% 2% 32,238 Septicemia 10 2% 2% 39,480 Kidney disorders 9 2% 3% 53,852 Alzheimer’s disease 8 3% 3% 62,034 Flu and pneumonia 7 3% 4% 71,372 Diabetes mellitus 6 4% 5% 101,537 Accidents 5 5% 6% 123,013 Chronic respiratory 4 7% 9% 163,538 Cerebrovascular 3 23% 29% 553,768 Cancer 2 29% 37% 700,142 Heart disease 1 Percent of...
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Chapter01 - Displaying data with graphs BPS chapter 1 ©...

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