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# chapter2 - CHAPTER 2 DISPLAYING AND DESCRIBING DATA 2.1...

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CHAPTER 2: DISPLAYING AND DESCRIBING DATA 2.1 Variables Consider a class of 30 students: Gender (male, female) Hair color (blond, brown, black,..) Height (in feet, inches) Weight (in pounds) Age (in years) ............ ............ Variable – any characteristic of a person or thing that can be expressed as a number or a label. Value the actual number or label assigned to a particular variable. VARIABLE POSSIBLE VALUES Gender male, female Hair color blond, brown, black,… Height 5’ 10’’, 6’1” Weight 160, 176, 180,… 1

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Variables Categorical Quantitative (values are labels) (values are numbers) Categorical variables: gender, hair color, marital status Quantitative variables: weight, height, age, income Describing Variables: Categorical: Specify the number (or percentage) of observations in each category. Quantitative: Determine the center (typical value) and spread (variability) of the data. Quantitative Variables Discrete Continuous (isolated points on the number line) (possible values form an interval ) 2
Example: Discrete variables: number of children in a household Continuous variables : weight, height, income. Frequency Tables Frequency Table for Categorical Variables – lists all possible values for a variable with the corresponding number of observations (and relative frequency) for each value. Gender Frequency Relative Frequency Males 18 0.60 Females 12 0.40 Frequency table for Quantitative Variable - based on counts of observations in each of several non-overlapping intervals of equal width covering the whole range of values. Weight (in pounds) Frequency Relative Frequency 140 or higher but smaller than 150 3 0.10 150 or higher but smaller than 160 6 0.20 3

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