Lecture1-2

Lecture1-2 - BUAD 310 Applied Business Statistics Data...

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BUAD 310 Applied Business Statistics 1/13/10
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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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Data Analysis Initial examination of the data is called Exploratory Data Analysis (EDA). Strategy for EDA: Begin by examining each variable and then move on to the study of relationships At each stage start with graphs and then add numerical summaries 4
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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 5
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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 6 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. 7
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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 8
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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 9
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Lecture1-2 - BUAD 310 Applied Business Statistics Data...

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