Chapter2

# Chapter2 - Chapter 2 Data Presentation Using Descriptive...

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Chapter 2 Data Presentation Using Descriptive Graphs

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2 2.1 Frequency Distributions The tabulation of data by dividing it into classes and computing the number of data points (or their fraction out of the total) falling within each class . Example: Grades on Business Statistics Exam Classes (Exam Score) Frequency (Number of Students) Below 50 28 50 and under 60 30 60 and under 70 36 70 and under 80 20 80 and under 90 90 90 and over 16 220
3 Constructing a Frequency Distribution Gather the sample data Gather the sample data Arrange the data in an ordered array Arrange the data in an ordered array Ascending Order: Lowest to highest Ascending Order: Lowest to highest Descending Order: Highest to lowest Descending Order: Highest to lowest Select the number of classes, Select the number of classes, K, K, to be used to be used There is no “correct” number of classes. There is no “correct” number of classes. Determine the class width, CW. Determine the class width, CW. K Range K L H CW = - = Determine the class limits for each class Determine the class limits for each class Count the number of data values in each class (the class frequencies) Count the number of data values in each class (the class frequencies) Summarize the class frequencies in a frequency distribution table Summarize the class frequencies in a frequency distribution table Where: H = Highest Value L = Lowest Value Rounded up or down to a value that is easy to interpret.

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4 Constructing a Frequency Distribution (cont.) Example: Frequency Distribution for Continuous Data Fifty starting salaries for business majors at Bellaire College Raw Data 41.5 39.4 40.9 35.9 37.4 39.5 40.3 39.3 41.6 36.6 41.1 35.7 43.7 37.0 41.3 40.6 38.0 42.4 35.7 41.4 39.2 36.8 39.3 43.8 38.5 43.0 36.3 35.6 36.2 38.1 34.8 38.1 35.7 36.5 39.5 37.9 34.3 36.8 33.8 35.0 37.8 38.7 37.2 32.8 38.2 37.0 39.7 38.8 35.2 36.2
5 Constructing a Frequency Distribution (cont.) Example: Arrange the data in an ordered array Arrange the data in an ordered array Ordered Array 32.8 33.8 34.3 34.8 35.0 35.2 35.6 35.7 35.7 35.7 35.9 36.2 36.2 36.3 36.5 36.6 36.8 36.8 37.0 37.0 37.2 37.4 37.8 37.9 38.0 38.1 38.1 38.2 38.5 38.7 38.8 39.2 39.3 39.3 39.4 39.5 39.5 39.7 40.3 40.6 40.9 41.1 41.3 41.4 41.5 41.6 42.4 43.0 43.7 43.8

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6 Constructing a Frequency Distribution (cont.) Example:
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Chapter2 - Chapter 2 Data Presentation Using Descriptive...

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