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Unformatted text preview: Stat 104: Quantitative Methods for Economists Class 3: Graphs and Summarizing DataMeasures of Center 1 Describing Data : Graphically and Numerically s Assuming we have generated a random sample of data from some population (everyone in the population is equally likely to be selected), we need methods to analyze the data, both graphically and numerically. s This section of the notes presents two graphical techniques (the dotplot and histogram ) and several summary measures ( mean , median, mode) for dealing with sample data . 2 Types of data s Data are the statisticians raw material, the numbers we use to interpret reality. All statistical problems involve either the collection, description and analysis of data, or thinking about the collection, description and analysis of data. s There are many aspects of data. Data may be univariate (one variable per case) or multivariate (more than one variable per case). There are also different types of data: discrete and continuous. How many cats do you own ? What is your weight ? 3 Some data to play with s A young college graduate in his first teaching assignment in a local school district decided to introduce his first grade class to statistics. s As a class exercise, he brought in a scale and a tape measure and recorded the height (in inches) and weights (in pounds) of all 73 students in his two homeroom classes. 4 Here is the class data (classdata1.xls) 62.00 49.00 37.50 42.00 56.00 46.00 38.00 40.25 43.50 45.50 46.00 51.00 38.50 39.00 40.00 42.00 59.00 42.00 48.00 43.75 48.50 42.00 47.00 44.50 48.00 46.00 52.50 43.00 34.00 40.00 32.00 40.00 39.75 42.50 46.50 44.50 42.75 44.00 50.00 47.25 63.50 45.50 60.00 46.00 72.00 45.50 31.50 43.50 35.00 38.50 41.25 46.25 41.00 42.00 31.00 42.00 43.50 44.00 49.00 46.00 40.00 42.25 41.00 45.25 48.00 48.00 40.00 44.00 46.25 46.25 34.25 40.75 30.00 40.25 36.50 43.25 40.50 43.50 43.50 44.50 34.75 41.25 45.00 43.00 43.75 45.75 60.00 44.00 37.25 40.25 43.50 42.00 51.00 45.00 34.25 41.50 57.50 39.50 39.00 31.00 46.00 44.50 35.25 43.25 41.25 45.25 48.75 45.25 34.50 39.00 42.50 43.25 40.50 46.25 41.75 41.00 44.50 45.50 47.50 44.50 53.00 49.00 39.50 44.25 45.25 44.50 49.50 46.00 42.00 49.00 43.50 46.00 36.00 40.00 43.50 43.50 33.75 42.50 45.50 44.50 36.50 43.50 53.00 43.00 38.50 41.00 Without reading ahead, which column is weight and which is height ?? 5 The Dotplot s Clearly we need a graphical way to display the data so we can see what is going on. simple graphical method is called the s A simple graphical method is called the dotplot; one dot per student goes over each students reported weight and height. 6 The Dotplot . : : . ::..: : .. . .:. .::.:::::::::.::::::... : . . .: .. ....
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 Fall '11
 MichaelParzen
 Mean, Median, Mode

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