Lecture4-1

Lecture4-1 - BUAD 310 Applied Business Statistics Quiz 1...

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BUAD 310 Applied Business Statistics Quiz 1 Review 2/1/10
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Data Consists of values of some variables measured or observed for some individuals . E.g., the data set from the class survey (14 variables for the students in our class). Variable is a characteristic of an individual. Qualitative or Categorical : places an individual into one of several groups or categories (finitely many possible) Quantitative : measurements represent quantities, e.g. “how many” (infinitely many possible) 2
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Scales of Measurement Ratio variable Quantitative scale (almost all) Ratios meaningful, inherently defined zero ( e.g., salary, weight, distance ) Interval variable Quantitative scale (very few) Ratios not meaningful, no inherently defined zero ( e.g., temperature ) Ordinal variable Qualitative (Categorical) scale Meaningful ordering or ranking of categories ( e.g., class ) Nominative variable Qualitative (Categorical) scale No meaningful ordering or ranking of categories ( e.g., gender, color ) 3
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Distribution of a Variable Describes what possible values the variable takes and how frequently it takes those values. We describe the overall pattern of a distribution by its shape, center, and spread. There are many ways to describe and display distributions. Graphs Word descriptions Numerical measures 4
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Qualitative (Categorical) Variables The values of a categorical variable are the labels for the categories. The distribution of a categorical variable is described by either the count or the percent of individuals who fall in each category. E.g., data on young American adults from the 1999 Current Population Survey 5 Education Count (millions) Percent Less than high school 4.7 12.3 High school graduate 11.8 30.7 Some college 10.9 28.3 Bachelor’s degree 8.5 22.1 Advanced degree 2.5 6.6
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Graphs for Categorical Variables Bar chart: the height of each bar is proportional to the count (or percent) in each category. 6
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Graphs for Categorical Variables The proportion (as percent) of all cars sold in the United States by different manufacturers, 1970 versus 1997 7
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Graphs for Categorical Variables Pie chart: the area of each piece is proportional to the percent of individuals in each category 8
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Graphs for Categorical Variables The proportion (as percent) of all cars sold in the United States by different manufacturers, 1970 versus 1997 9
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Histogram for Quantitative Variables 10 Histogram To make a histogram: Divide the range of the data set into equal intervals For each interval draw a bar with the base covering the interval and the height proportional to the count of observations that fall into the interval.
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Words that describe distributions Unimodal: has one major peak Bimodal: has two major peaks Symmetric: there is a symmetry with respect to the middle point Skewed to the right: when the right tail (larger values) is much longer than the left tail (smaller values) Skewed to the left: when the left tail (smaller values) is much longer than the right tail (larger values) 11
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Symmetric, Unimodal, Bimodal 12 Symmetric, unimodal Bimodal
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S k ewness 13 Skewed to the left Skewed to the right
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This note was uploaded on 09/05/2010 for the course BUAD 310 taught by Professor Lv during the Spring '07 term at USC.

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Lecture4-1 - BUAD 310 Applied Business Statistics Quiz 1...

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