CH-2 PPT

# CH-2 PPT - The Who, What, Why, Where, When and How of Data...

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The Who , What , Why , Where , When and How of Data

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Statistics consists of two parts: Descriptive statistics (coping with lots of numbers) 1. Draw a picture (graph, charts etc) 2. Calculate a few numbers which summarize the data (mean, median, percentile) Inferential statistics How can one make decisions and predictions about a population even if we have data for relatively few subjects from that population? We need to generalize the facts we learn from a sample ( i.e. a part of the population) to the entire population
Data types Let’s consider the following questions 1. What is your sex? 2. How tall are you? (inches) 3. What year are you in school? 4. What is your major? 6. How many miles do you travel to UMD each day? 7. What is your GPA?

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Variables Each question measures some aspect of you. Variable : the aspect/characteristic that differs from subject to subject, individual to individual. Age, Sex, Major,… Data : the value of the variables 20, Male, English, …
Two Types of Variables Quantitative or numerical variables Numbers, measurements Age, height, miles traveled Qualitative or categorical variables Classifying each observation Sex, year in school, major

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Quantitative or numerical variables Discrete variables : there is a natural gap between the values Number of children Number of credit cards Continuous variables : the values can be arbitrarily close together Weight Height Age
Qualitative or categorical variables Ordinal variables : categorie s that have a natural ordering Numbers could be assigned to categories Class 1 = Freshman 2 = Sophomore 3 = Junior 4 = Senior Grade A, B, C, D, F (GPA) Preference Strongly Agree, Agree, Disagree, Strongly Disagree Nominal variables : categories that have no natural ordering Major business, mathematics, history Eye color blue, green, black

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Types of variables summary variables qualitative quantitative discrete continuous nominal ordinal
Examples (What are the types?) 1. Appraisal of a company’s inventory level (excellent, good, fair, poor) 2. Mode of transportation to work. (automobile, bicycle, bus, subway, walk) 3. Speed of a vehicle 4. The number of persons in each family. 5.

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## This note was uploaded on 11/05/2011 for the course BMGT 220 taught by Professor Bulmash during the Spring '08 term at Maryland.

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CH-2 PPT - The Who, What, Why, Where, When and How of Data...

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