Chapter2

Chapter2 - Chapter 2 Describing Data: Graphical...

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Chapter 2 Describing Data: Graphical

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Introduction Once we have a mass of data, how do we get any meaningful information out of it? There are many ways to proceed depending on the type of data and the question we want to answer. In this chapter, we will focus on graphical description of a data. Graphical description of data takes many forms. We have to choose the appropriate form for each situation. We have to choose the graphical form that communicates best the results of the analysis.
2-1 Classification of variable: What type of variable do we have? Categorical variables produce responses that belong to groups or categories Example: Do you own a computer? (Yes/No) What is your favorite between tea and coffee? (tea/coffee) How did you like the last “Spiderman” movie? (not at all/not much/very much) Numerical variables include both discrete and continuous variables.

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Types of Variables Discrete variables generally come from a counting process. They may (but not necessarily) have a finite number of values Example: How many credit-hours are you taking this semester? How many states have you lived in? How many operations a computer can do in a minutes? Continuous variables may take any value within a given range of real numbers and usually arises from a measurement (not a counting) process. Example: Height, distance, weight, time and temperature.
Types of Variables Qualitative data: the difference in numbers has no measurable meaning for this type of data. There are two types of measurement levels for this type of data: nominal and ordinal. Nominal and ordinal levels of measurement refer to data obtained from categorical questions.

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Measurement Levels Nominal variables : their values are words that describe the categories or classes or responses. They are considered the lowest type of data, since numerical identification is chosen strictly for convenience.
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This note was uploaded on 04/29/2008 for the course EC 305 taught by Professor Rivas during the Fall '08 term at BU.

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Chapter2 - Chapter 2 Describing Data: Graphical...

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