ch 2 - Chapter 2: Frequency Distributions and Graphs 2.2:...

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Chapter 2: Frequency Distributions and Graphs 2.2: Frequency Distributions An equivalence class can be: a single score value,--ungrouped a collection of score values, or --grouped a qualitative category.—grouped Ex: all with brown hair A table showing the equivalence classes and the frequency with which their score values occur is called a frequency distribution . The equivalence classes in a frequency distribution are called class intervals . There are two types of frequency distributions: ungrouped – each class interval is a single score value grouped – each class interval spans two or more score values. A. Ungrouped Frequency Distributions Example Use the data from P. 39 # 2 to construct an ungrouped frequency distribution. Data Ungrouped frequency distribution 3 7 10 4 7 10 4 7 10 4 7 10 5 7 11 5 7 11 5 7 11 5 8 11 6 8 12 6 8 13 6 8 15 6 8 15 6 8 17 6 8 21 8 22 9 25 9 9 9 9 number frequency 3 1 4 3 5 4 6 6 7 7 8 8 9 5 10 4 11 4 12 1 13 1 15 2 17 1 21 1 22 1 25 1 Total 50 1
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**Don’t leave gaps in number column, put all numbers in range and if no freq. just leave blank/put 0. B. Grouped Frequency Distributions 1) Pros and Cons of Grouping Data 1. Pros 1. easy to understand for a large data set 2. can express data visually through graphs 3. reduces labor required in computing statistics 2. Cons 1. information is lost 2. rules used to construct grouped frequency distributions don’t always produce unique distributions 2) Bins or class interval (p34) 1. Requirements of a class interval 1. class intervals should not overlap (not 2-4,4-5…cant have four in both) 2. for quantitative variables there should be no gaps between the class intervals even when no data falls in them (i.e ., include on table even if frequency is zero ) 3. all quantitative class intervals should have the same width or size 4. prefer 10 to 20 class intervals unless the amount of data is really small
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This note was uploaded on 04/15/2008 for the course STATS 2402 taught by Professor Kirk during the Spring '08 term at Baylor.

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ch 2 - Chapter 2: Frequency Distributions and Graphs 2.2:...

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