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# Lesson1 - Lesson 1 Author Atul Roy Remember to read the...

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Lesson 1 Author: Atul Roy Remember to read the definitions of Numerical or Quantita t ive Data Categorical or Qualitative data Descriptive Statistics Inferential Statistics Distribution of the data Topic 1. Organization and Display of Numerical Data Example 1. The following data shows the prices of the townhomes on Truffle Lane in Montgomery County, Maryland. The data is obtained from the real property search data base of the State of Maryland. The townhomes were built and sold in the year 2000-2001 and the prices are the initial purchase prices of the homes. Since all the houses were over \$200,000 the list shows only the amount that was paid in excess of \$200,000 rounded to the nearest thousandth. price paid (over \$200,000) 67 25 38 36 31 24 45 72 30 5 13 1 2 63 53 21 5 77 34 16 15 39 45 19 23 23 12 31 25 12 23 33 58 T hat is the number 67 means that the house was sold for \$267,000 (rounded.) One way to organize and display such data is called Stem and Leaf Diagram Since an ordered Stem and Leaf Diagram is more meaningful, let us first put the data in order 1 2 5 5 12 12 13 15 16 19 21 23 23 23 24 25 25 30 31 31 33 34 36 38 39 45 45 53 58 63 67 72 77 Treating all the numbers as two digit numbers, that is 1 as 01 etc., we may use the first digit as stem and the second digit as leaf and the display will be 1

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0*1255 1*223569 2*1333455 3*01134689 4*55 5*38 6*37 7*27 Note that a stemplot will give an idea of the shape of a distribution. It will help you visually locate the outliers (we shall see a well formulated approach to outliers in the lesson 2.) It helps us locate the vital numbers, for example 0*1255 1*223569 2*133345 5 3*01134689 4*55 5*38 6*37 7*27 you may see that 25 is in the center of the distribution in the sense that it is right in the middle, telling us that half of the homes were sold at 225,000 or below. Such a value is called the median of the data, we shall take median up more in detail in the lesson 2.
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