# chapter1 - Introduction to Probability and Statistics...

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9/1/2011 1 Introduction to Probability and Statistics Thirteenth Edition Chapter 1 Describing Data with Graphs Variables and Data • A variable is a characteristic that changes or varies over time and/or for different individuals or objects under consideration. Examples: Hair color, white blood cell count, time to failure of a computer component. Definitions • An experimental unit is the individual or object on which a variable is measured. • A measurement results when a variable is actually measured on an experimental unit. • A set of measurements, called data , can be either a sample or a population . Example Variable –Hair color Experimental unit –Person Typical Measurements –Brown, black, blonde, etc.

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9/1/2011 2 Example Variable Time until a light bulb burns out Experimental unit –Light bulb Typical Measurements –1500 hours, 1535.5 hours, etc. How many variables have you measured? Univariate data : One variable is measured on a single experimental unit. Bivariate data : Two variables are measured on a single experimental unit. Multivariate data : More than two variables are measured on a single experimental unit. Types of Variables Qualitative Discrete Continuous Quantitative Types of Variables Qualitative variables measure a quality or characteristic on each experimental unit. Examples: •Hair color (black, brown, blonde…) •Make of car (Dodge, Honda, Ford…) •Gender (male, female) •State of birth (California, Arizona,….)
9/1/2011 3 Types of Variables Quantitative variables measure a numerical quantity on each experimental unit. Discrete if it can assume only a finite or countable number of values. Continuous if it can assume the infinitely many values corresponding to the points on a line interval. Examples

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chapter1 - Introduction to Probability and Statistics...

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