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Chapter 1

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STAT 101
Qian( Michelle) Zhou

Chapter 1 • Statistics = science of data Individuals and Variables • individuals – objects described by a set of data (ex. People, animals, things) • variable – any characteristics of an individual (ex. Eye colour etc) • categorical variable – places individuals into one of several groups/categories • quantitative variable – takes numerical value; usually recorded in unit of measurement (ex. Kg) Categorical Variables: Pie Charts and Bar Graphs • explanatory data analysis – stat tools/ideas that help examine data to describe main features ◦ first, examine each variable by itself, the move on to study relationships among variables ◦ begin w/ a graph(s), then add numerical summaries of specific aspects of data • proper choice of graph depends on nature of variable; want to display it's distribution ◦ distribution of variable – tells us what values it takes and how often it takes these values ◦ distribution of a categorical variable – lists categories and gives either count or percent of individuals who fall in each category example 1.2- which major? • Percents should add up to 100%; actually 99.9% ◦ why? Each percent is rounded to nearest tenth ◦ roundoff error – just effect of rounding off results • Pie charts – show distribution of categorical variable as a “pie” ◦ must include all the categories that make up a whole ◦ only use when you want to emphasize each category's relation to whole • Bar graphs – represent each category as a bar ◦ bar heigh shows counts or % ◦ more flexible than pie ◦ can compare any set of quantities that are measured in same units Apply Your Knowledge 1.3Do you listen to talk radio? (pg. 10) a) 12.6+12.5+....2.5 = 67.3 sum of audience shares; 32.7% for other formats c) it can b/c the sum can add up to a 100 1.4How do students pay for college (pg.11) a) not correct to use pie charts b/c these numbers are way too big to add up to a 100 1.5Never on a Sunday (pg.11) a) No, values are way too big and they don't add up to a 100 Quantitative Variables: Histo
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